Water treatment equipment

Abstract

To provide a water treatment apparatus capable of removing a predetermined substance and increasing the volume of treated water that can be discharged.SOLUTION: A water treatment apparatus 1 includes: a raw water tank 2 for storing raw water containing a predetermined substance; at least one reverse osmosis membrane device 6 for separating raw water pumped from the raw water tank 2 into permeated water and concentrated water; a concentrated water circulation line L5 for returning concentrated water to the raw water tank 2; a treated water tank 7 for storing the permeated water as the treated water; and concentration acquiring means 10 for acquiring the concentration of a predetermined substance in the treated water stored in the treated water tank 7. When the concentration acquired by the concentration acquisition means 10 reaches a predetermined value, at least a part of the treated water stored in the treated water tank 7 is discharged from the treated water tank 7.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment device, and more particularly to a water treatment device for removing boron from boron-containing water. [Background technology]

[0002] Water treatment systems that use reverse osmosis membranes to remove boron from industrial and power plant wastewater are known. The WHO (Japan) established a drinking water standard for boron (1 mg / L) and established wastewater discharge standards (230 mg / L in marine areas and 10 mg / L in land areas in Japan). Boron is also found in seawater (approximately 4–5 mg / L). Boron exists in water in equilibrium with boric acid and borate ions. Boron in the form of boric acid (non-ionized boron) is particularly permeable to reverse osmosis membranes. Therefore, boron is often found in high concentrations in wastewater, but is also difficult to remove. Therefore, to increase the boron removal rate, a recirculation system is sometimes used in which the concentrated water from the reverse osmosis membrane system is returned to the reverse osmosis membrane system (Patent Documents 1 and 2). Returning the concentrated water to the reverse osmosis membrane system increases the boron concentration in the concentrated water and facilitates volume reduction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-144997 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-237986 Summary of the Invention [Problem to be solved by the invention]

[0004] In the water treatment devices disclosed in Patent Documents 1 and 2, the boron concentration of the inlet water of the reverse osmosis membrane device increases over time. However, the boron rejection rate of the reverse osmosis membrane device, i.e., the ratio of the boron concentrations on the primary side (concentration side) and secondary side (permeation side) of the reverse osmosis membrane device, is nearly constant regardless of the boron concentration in the raw water. Therefore, the boron concentration on the secondary side of the reverse osmosis membrane also increases over time. As mentioned above, when the boron concentration in the treated water reaches a predetermined discharge standard value, the treated water cannot be discharged. Therefore, it is necessary to drain the raw water from the primary side and replace it with raw water with a lower boron concentration. Therefore, with conventional technologies, it is difficult to increase the amount of treated water that can be discharged. Similar issues exist for substances other than boron.

[0005] An object of the present invention is to provide a water treatment device that can remove predetermined substances and increase the amount of treated water that can be released. [Means for solving the problem]

[0006] The water treatment device of the present invention comprises: Boron a raw water tank for storing raw water containing the above; at least one reverse osmosis membrane device for separating the raw water sent from the raw water tank into permeate water and concentrated water; a concentrated water circulation line for returning the concentrated water to the raw water tank; a treated water tank for storing the permeate water as treated water; Boron and a concentration acquisition means for acquiring the concentration of the water. When the concentration acquired by the concentration acquisition means reaches a predetermined value, at least a portion of the treated water stored in the treated water tank is discharged from the treated water tank. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a water treatment device that can remove predetermined substances and increase the amount of treated water that can be released. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a water treatment device according to a first embodiment of the present invention. [Figure 2]FIG. 10 is a diagram illustrating an example of the relationship between processing time and a density correlation parameter. [Figure 3] FIG. 4 is a schematic configuration diagram of a water treatment device according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a schematic configuration diagram of a water treatment device according to a third embodiment of the present invention. [Figure 5] FIG. 10 is a schematic configuration diagram of a water treatment device according to a first modified example of the third embodiment of the present invention. [Figure 6] FIG. 10 is a schematic configuration diagram of a water treatment device according to a second modified example of the third embodiment of the present invention. [Figure 7] FIG. 10 is a schematic configuration diagram of a water treatment device according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Several embodiments of the water treatment device of the present invention will be described below with reference to the drawings. In the following embodiments, a reverse osmosis membrane device is provided to remove boron from raw water, but the raw water may contain a predetermined substance that can be removed by the reverse osmosis membrane device. In this embodiment, the predetermined substance is boron, but the predetermined substance is not limited to boron. The boron concentration of the target raw water is not limited, but is, for example, on the order of tens to thousands of ppm.

[0010] (First embodiment) FIG. 1 shows a schematic configuration of a water treatment device 1 according to a first embodiment of the present invention. The water treatment device 1 has a raw water tank 2 that stores raw water containing boron. The raw water is boron-containing wastewater discharged from boron-handling facilities such as factories, power plants, hot spring facilities, waste landfills, and mines. A raw water supply line (hereinafter referred to as a raw water supply line L1) is connected to the raw water tank 2, and a first valve V1 is provided on the raw water supply line L1. The water treatment device 1 has at least one reverse osmosis membrane device 6 (one in this embodiment) that separates the raw water supplied from the raw water tank 2 into permeate and concentrate. The reverse osmosis membrane device 6 is divided by a reverse osmosis membrane 61 into a concentrate side space 62 where the raw water is concentrated and a permeate side space 63 where the permeate passes through. Reverse osmosis membranes 61 are classified into high-pressure, medium-pressure, low-pressure, and ultra-low-pressure types depending on the pressure acting on the membrane, but any type can be used in this embodiment. However, because the boron rejection rate is higher in high-pressure reverse osmosis membranes, it is preferable to use high-pressure reverse osmosis membranes, especially when the boron concentration in raw water is high. High-pressure reverse osmosis membranes generally have a permeation flux of 0.3 to 0.65 m per 1.0 MPa effective membrane surface pressure at 25°C. 3 / m 2 / day, and the NaCl removal rate is 99.5% or higher. Between the raw water tank 2 and the reverse osmosis membrane device 6, a pump 3 for pumping the raw water from upstream to downstream along the raw water supply direction, a filter 4 for removing impurities and dust from the raw water, and a pH adjustment means 5 for adjusting the pH of the raw water are installed in series. The filter 4 may be a mesh strainer, an ultrafiltration membrane (UF membrane), a microfiltration membrane (MF membrane), or a safety filter. The boron removal efficiency improves by increasing the pH. The pH is preferably 5 to 9, but is not limited thereto. The installation of the filter 4 and the pH adjustment means 5 is optional, and either or both may be omitted. The filter 4 and the pH adjustment means 5 may also be installed upstream of the raw water tank 2.

[0011] The water treatment device 1 has a treated water tank 7 that stores permeated water. The permeate side space 63 of the reverse osmosis membrane device 6 is connected to the treated water tank 7 by a permeate line L2. A second valve V2 is provided on the permeate line L2. As will be described in detail later, the treated water tank 7 is a characteristic feature of this embodiment. The permeated water that has permeated through the reverse osmosis membrane device 6 is not directly discharged but is temporarily stored in the treated water tank 7. The treated water tank 7 is connected to a discharge line L3, which is provided with a third valve V3. A concentrated water discharge line L4 is connected to the raw water tank 2, which is provided with a fourth valve V4. The concentrated side space 62 of the reverse osmosis membrane device 6 and the raw water tank 2 are connected by a concentrated water circulation line L5 that returns the concentrated water to the raw water tank 2. If the raw water tank 2 is small, the discharge pressure of the pump 3 is high, or the permeated water volume is set low, the temperature of the raw water may increase due to the circulation of the concentrated water. For this reason, a heat exchanger L13 for cooling the concentrated water is provided in the concentrated water circulation line L5, and the temperature can be lowered if the temperature of the concentrated water becomes high. The heat exchanger L13 can be of a shell-and-tube type or a plate type. The heat exchanger L13 can also be omitted. The valves V1 to V4 shown in FIG. 1 show the state during batch operation of the water treatment device 1. In the following explanation, permeated water refers to the water in the permeate side space 63 of the reverse osmosis membrane device 6, and is synonymous with the outlet water of the reverse osmosis membrane device 6. Treated water refers to the water stored in the treated water tank 7. As will be described later, permeated water and treated water are different.

[0012] The water treatment device 1 includes a concentration acquisition means 10 that acquires the boron concentration in the treated water stored in the treated water tank 7. While the concentration acquisition means 10 may be a boron concentration meter provided in the treated water tank 7, this embodiment employs a method of indirectly calculating the boron concentration in the treated water from other measured values. As described below, the boron concentration in the treated water is correlated with a predetermined concentration correlation parameter. The concentration correlation parameter is at least one of the water volume in the raw water tank 2, the water volume in the treated water tank 7, and the elapsed time since the start of treatment in the reverse osmosis membrane device 6 (hereinafter referred to as the treatment time). The concentration correlation parameter can be measured by concentration correlation parameter measurement means 8, 9. The concentration correlation parameter measurement means 8, 9 includes a first water level gauge 8 that measures the water level in the raw water tank 2 to obtain the water volume in the raw water tank 2, and a second water level gauge 9 that measures the water level in the treated water tank 7 to obtain the water volume in the treated water tank 7. The water treatment device 1 may also include a timer (not shown) for measuring the treatment time in the reverse osmosis membrane device 6. In the figure, a first water level gauge 8 and a second water level gauge 9 are shown as examples of the concentration correlation parameter measuring means 8, 9. The concentration acquiring means 10 has means for converting the measurement values ​​of the concentration correlation parameter measuring means 8, 9 into the boron concentration in the treated water stored in the treated water tank 7. The concentration acquiring means 10 then calculates the average boron concentration in the treated water stored in the treated water tank 7 based on the concentration correlation parameters measured by the concentration correlation parameter measuring means 8, 9, and determines whether the calculated average boron concentration has reached a predetermined value. The concentration acquiring means 10 is incorporated, for example, as a program in the control device of the water treatment device 1, but the operator can also determine the average boron concentration in the treated water from the measurement values ​​of the concentration correlation parameters and a conversion table.

[0013] (Operation method of water treatment device 1) Next, a method of operating the water treatment device 1 will be described. First, the first valve V1 and the second valve V2 are opened, and the third valve V3 and the fourth valve V4 are closed. Raw water is supplied to the raw water tank 2 from the raw water supply line L1, and when a predetermined amount of raw water is stored in the raw water tank 2, the first valve V1 is closed. The raw water is supplied from tower tanks such as a raw water tank and a wastewater tank that store a large amount of boron-containing water, or from other water treatment facilities (not shown). In this embodiment, the water treatment device 1 is operated in batch operation (batch-type treatment). Therefore, during batch operation, the first valve V1, the third valve V3, and the fourth valve V4 are closed, and no water flows in or out of the water treatment device 1.

[0014] Next, the pump 3 is started to pump the raw water to the reverse osmosis membrane device 6, where it is treated. The water supply flow rate and circulating water flow rate (flow rate in the concentrated water circulation line L5) are selected so as to ensure the minimum required flow rate determined for each membrane type of the reverse osmosis membrane device 6. The permeate flow rate (flow rate in the permeate line L2) is adjusted by the aperture of the second valve V2 so as not to deviate from the membrane's water flow conditions. The second valve V2 may be a constant flow valve or an adjusting valve. Alternatively, the permeate flow rate may be controlled by the rotation speed of the pump 3. Of the boron contained in the raw water, an amount equivalent to the boron rejection rate of the reverse osmosis membrane 61 is removed, and the remainder permeates into the permeate space 63. The boron rejection rate is calculated by (AB) / A, where A is the boron concentration of the inlet water of the reverse osmosis membrane device 6 and B is the boron concentration of the outlet water of the reverse osmosis membrane device 6. The permeated water that has permeated into the permeate side space 63 passes through the permeate line L2 and is stored as treated water in the treated water tank 7. The raw water remaining in the concentrated side 62 is returned as concentrated water to the raw water tank 2 through the concentrated water circulation line L5 and is then pumped again to the reverse osmosis membrane device 6 by the pump 3.

[0015] As the above process is repeated, the amount of raw water in the raw water tank 2 gradually decreases, and the amount of treated water in the treated water tank 7 gradually increases. In addition, because the concentrated water is returned to the raw water tank 2, the boron concentration in the raw water tank 2 gradually increases. That is, the total amount of boron contained in the raw water gradually decreases, but the amount of raw water also decreases at an even greater rate, so the boron concentration in the raw water gradually increases. Therefore, as the treatment continues, the boron concentration in the permeate also gradually increases.

[0016] 2 shows an example of calculation of the relationship between the water level in the raw water tank 2, the boron concentration in the raw water in the raw water tank 2, the boron concentration in the permeate water from the reverse osmosis membrane device 6, and the average boron concentration in the treated water from the treated water tank 7, and the treatment time. This calculation is performed when raw water with a boron concentration of 500 mg / L (ppm) is supplied to the raw water tank 2 up to a water level of 3.9 m (volume 10,000 L), and a constant permeate volume of 1.5 m is supplied. 3 This is a calculation example when raw water is treated by the reverse osmosis membrane device 6 at a rate of 1 / h. The initial water level in the treated water tank 7 is 0 m. The boron rejection rate of the reverse osmosis membrane device 6 is set to 80%. When the average boron concentration in the treated water in the treated water tank 7 reaches 200 mg / L (an example of the standard value for the boron concentration at which water can be discharged), the water flow time is approximately 5.6 hours, the water level in the raw water tank 2 is approximately 0.7 m, and the boron concentration in the raw water in the raw water tank 2 is approximately 2100 mg / L (ppm).

[0017] As can be seen from this diagram, as treatment progresses, the water level (volume) of raw water tank 2 decreases, while the boron concentration in the raw water in raw water tank 2, the boron concentration in the permeate water from reverse osmosis membrane device 6, and the average boron concentration in the treated water from treated water tank 7 increase. The boron concentration is highest in raw water tank 2 and lowest in treated water tank 7, with the permeate water from reverse osmosis membrane device 6 lying in between. Importantly, the water level (volume) of raw water tank 2, the boron concentration in the raw water in raw water tank 2, the boron concentration in the permeate water from reverse osmosis membrane device 6, the average boron concentration in the treated water from treated water tank 7, and the treatment time are all correlated, so knowing any one of these values ​​makes it possible to estimate the other values. Furthermore, because batch treatment is performed, the total volume of water stored in raw water tank 2 and treated water tank 7 remains constant. Therefore, the water level (volume) of treated water tank 7 can be used instead of or in addition to the water level (volume) of raw water tank 2.

[0018] The most reliable way to measure boron concentration is with a boron concentration meter. However, boron concentration meters are very expensive. Therefore, in this embodiment, instead of using a boron concentration meter, the water level (water volume) in the raw water tank 2, the water level (water volume) in the treated water tank 7, and the treatment time are used as concentration correlation parameters. When treatment time is used as the concentration correlation parameter, a constant permeation treatment volume is required. In the example of Figure 2, the concentration acquisition means 10 determines that the boron concentration has reached the upper limit of the releasable concentration (200 mg / L (ppm)) when the water flow time is approximately 5.6 hours, the water level in the raw water tank 2 is approximately 0.7 m, and the water level in the treated water tank 7 is approximately 3.2 m (3.9 m - 0.7 m). At this time, the concentration acquisition means 10 issues an alarm, and the operator may stop the water treatment device 1 in response. Alternatively, the boron concentration acquired by the concentration acquisition means 10 may be transmitted to the control device of the pump 3, causing the control device to automatically stop the pump 3. In either case, it is preferable to allow a margin for the water discharge standard value and stop the batch operation of the water treatment device 1 when the boron concentration reaches a value slightly lower than the water discharge standard value.

[0019] To perform the above-described control, it is desirable to know the boron concentration of the raw water in advance. It is also desirable to know in advance the linear velocity (LV), pH, temperature, and other factors of the raw water that affect the boron rejection rate. Specifically, first, the boron concentration, pH, and temperature of the raw water are measured to determine the quality of the raw water. Next, the membrane area of ​​the reverse osmosis membrane 61 is set based on the required treatment volume, and the LV of the raw water to be supplied to the reverse osmosis membrane device 6 is calculated. Next, the boron rejection rate of the reverse osmosis membrane 61 to be used is set based on these water quality and LV conditions. The boron rejection rate is determined in advance for these conditions. The boron rejection rate varies depending on the LV, pH, and temperature, but is typically around 50 to 95%. From these conditions, the volume of treated water after, for example, one hour can be calculated. The boron concentration in the treated water can be calculated from the boron rejection rate, and the boron concentration in the concentrated water can be calculated from the amount of rejected boron. By performing the same calculation after 2, 3, and 4 hours, the volume of treated water and the total amount of boron contained in the treated water can be calculated, and the average boron concentration in the treated water can be calculated. Performing this calculation more precisely can improve accuracy. In this way, the relationship between the concentration correlation parameter and the average boron concentration in the treated water, as shown in Figure 2, can be grasped in advance, and the operation of the water treatment device 1 can be managed. The operation of the water treatment device 1 can also be managed by monitoring multiple concentration correlation parameters in a composite manner.

[0020] It is also possible to use a boron concentration meter. In this case, there is no need to use the concentration correlation parameter, and batch operation is stopped when or before the boron concentration measured by the boron concentration meter reaches the water discharge standard value. It is preferable to constantly monitor the boron concentration with a boron concentration meter.

[0021] When the batch operation of the water treatment device 1 is completed (i.e., when the boron concentration acquired by the concentration acquisition means 10 reaches a predetermined value), the third valve V3 is opened, and at least a portion (in this embodiment, the entire amount) of the treated water stored in the treated water tank 7 is discharged from the treated water tank 7. The treated water stored in the treated water tank 7 may be sent to a separate treated water tank (not shown) to be released after its quality is confirmed, or it may be sent to a wastewater treatment facility (not shown). Simultaneously, or before or after this, the fourth valve V4 is opened, and at least a portion (in this embodiment, the entire amount) of the water (concentrated water) stored in the raw water tank 2 is discharged from the raw water tank 2. The concentrated water is sent to a concentrated water tank (not shown) and subjected to coagulation and sedimentation treatment. Since the boron concentration is increased, efficient treatment is possible. Alternatively, the concentrated water may be concentrated using an evaporative concentration device to further concentrate the treated water. Since the concentrated water has already been concentrated and reduced in volume, the equipment scale and operating costs of the coagulation and sedimentation treatment device and the evaporative concentration device can be reduced. After the evaporative concentration process, a solidification process may be performed.

[0022] Next, the effects of this embodiment will be described. When discharging permeate containing boron, if the boron concentration exceeds the water discharge standard value, the water cannot be discharged. Because the water treatment device 1 of this embodiment uses a recirculation system, the boron concentration in the permeate from the reverse osmosis membrane 61 gradually increases, as described above. Here, a comparative example is provided in which the treated water tank 7 is omitted from this embodiment. In this comparative example, the permeate from the reverse osmosis membrane device 6 is sequentially discharged while confirming that the boron concentration does not exceed the water discharge standard value. In this case, in FIG. 2, after about 4 hours, the boron concentration in the permeate from the reverse osmosis membrane device 6 reaches the water discharge standard value (200 ppm), and water cannot be discharged.

[0023] In contrast, in this embodiment, the permeated water from the reverse osmosis membrane device 6 is temporarily stored in the treated water tank 7. Because the boron concentration in the treated water from the treated water tank 7 is low in the initial stage after treatment begins, the permeated water with a high boron concentration that flows into the treated water tank 7 later is, so to speak, "diluted" or "averaged" by the permeated water with a low boron concentration that flows into the treated water tank 7 earlier. As a result, the average boron concentration in the treated water from the treated water tank 7 is kept lower than the boron concentration in the permeated water from the reverse osmosis membrane device 6 at the time of calculating the average boron concentration. Nevertheless, the boron concentration in the permeated water from the reverse osmosis membrane device 6 gradually increases, so the average boron concentration in the treated water from the treated water tank 7 also gradually increases. However, as mentioned above, it takes 5.6 hours for the permeated water to reach the discharge standard value (200 ppm). Therefore, while only about 4 hours' worth of permeated water can be discharged in the comparative example, in this embodiment, 5.6 hours' worth of permeated water, or about 40% more, can be discharged while complying with regulations. In other words, permeate whose boron concentration exceeds the discharge standard can be discharged by "diluting" or "averaging." Furthermore, even if the boron concentration in the permeate from the reverse osmosis membrane device 6 exceeds the discharge standard, the water treatment device 1 can continue to operate, allowing for longer batch operation than in the comparative example. As a result, the water level in the raw water tank 2 drops, enabling further volume reduction of the concentrated water. Components other than boron contained in the raw water can also be left in the concentrated water if they can be blocked by the reverse osmosis membrane device 6. Because the volume of the concentrated water has been reduced, if recovery or post-treatment of the components is required, the burden of recovery or post-treatment can be reduced.

[0024] It has been known for some time that boron permeates the reverse osmosis membrane when treating boron-containing water with a reverse osmosis membrane device. Therefore, improving the boron removal rate has been a key issue in the development of devices and materials. However, the idea of ​​adjusting the boron concentration in the permeated water while allowing boron to permeate has not been considered. Furthermore, the idea of ​​allowing the water treatment device 1 to continue operating after the boron concentration in the permeated water exceeds the discharge standard has not been considered. This embodiment is based on the novel idea of ​​installing a treated water tank 7 and adjusting the average boron concentration in the treated water in the treated water tank 7 to within the discharge standard. As a result, after the boron concentration in the permeated water from the reverse osmosis membrane device 6 exceeds the discharge standard, it is no longer necessary to remove the boron contained in the permeated water through a separate process or to adjust the permeated water to the desired concentration by diluting it with pure water or the like. This embodiment only requires the installation of the treated water tank 7, and therefore has limited impact on costs.

[0025] (Second embodiment) FIG. 3 shows a schematic configuration of a water treatment device 1 according to a second embodiment of the present invention. The water treatment device 1 includes an ion exchanger 11 connected to a treated water tank 7. The treated water tank 7 and the ion exchanger 11 are connected by a treated water circulation line L6, and the treated water stored in the treated water tank 7 circulates between the tank and the ion exchanger 11 along the treated water circulation line L6. This allows boron contained in the treated water to be adsorbed onto the ion exchange resin, thereby reducing the boron concentration in the treated water. When discharging the treated water, it is desirable to perform a final check to ensure that the boron concentration meets the discharge standard. However, if the boron concentration exceeds the discharge standard, the ion exchanger 11 reduces the boron concentration in the treated water to below the discharge standard before discharging it. Because continuous monitoring of the boron concentration is not necessary, the treated water in the treated water tank 7 can be sampled and measured using a commercially available boron concentration measurement kit (no expensive boron concentration meter is required). The ion exchange resin packed in the ion exchanger 11 is not particularly limited as long as it is an anion exchange resin, but is preferably one that selectively adsorbs boron, such as a basic anion exchange resin with a polyhydric alcohol functional group (e.g., DuPont IRA-743). The ion exchanger 11 is not operated continuously, but is only operated temporarily when the boron concentration in the treated water exceeds the release standard value, so a non-regenerative type is preferred. Using a regenerative type requires regeneration equipment, which complicates the water treatment device 1 and increases costs.

[0026] (Third embodiment) 4 shows a schematic configuration of a water treatment device 1 according to a third embodiment of the present invention. The water treatment device 1 of this embodiment has multiple reverse osmosis membrane devices 6A, 6B connected in series. In the following embodiments, when there are pumps 3, filters 4, pH adjusting means 5, heat exchangers 13, valves, etc. corresponding to the reverse osmosis membrane devices 6A, 6B, respectively, the reference numerals A and B may be added in the drawings, and their description may be omitted.

[0027] If the boron concentration in the raw water is high, a single-stage reverse osmosis membrane treatment may not be sufficient to reduce the boron concentration. In this embodiment, two reverse osmosis membrane devices 6A and 6B are provided. Therefore, if the boron rejection rate per stage is 80%, the total boron rejection rate for the two reverse osmosis membrane devices 6A and 6B is 96%, significantly improving the boron rejection rate. The number of reverse osmosis membrane devices 6A and 6B is not limited. An intermediate storage tank 12 is provided between the reverse osmosis membrane devices 6A and 6B. The intermediate storage tank 12 stores the permeated water from the upstream reverse osmosis membrane device 6A and delivers the permeated water to the downstream reverse osmosis membrane device 6B. The intermediate storage tank 12 can absorb the difference in permeated water volume between the reverse osmosis membrane devices 6A and 6B, thereby facilitating control of the water treatment device 1. The intermediate storage tank 12 may be omitted. The concentrated water from the two-stage reverse osmosis membrane devices 6A, 6B is returned to the raw water tank 2 through the respective concentrated water circulation lines L5A, L5B, but it is also possible to return part of the concentrated water from the latter-stage reverse osmosis membrane device 6B to the intermediate storage tank 12 and the remainder to the raw water tank 2. For this purpose, a concentrated water return line L7 is provided that branches off from the concentrated water circulation line L5B and is connected to the intermediate storage tank 12. The concentrated water return line L7 can also be omitted.

[0028] FIG. 5 shows a schematic configuration of a water treatment device 1 according to a first modified example of the third embodiment. The water treatment device 1 of this modified example has a configuration in which, when the water treatment device 1 of the first embodiment is combined into a single unit, multiple units UA and UB are arranged in series. However, the treated water tank 7 of the first-stage unit UA and the raw water tank 2 of the second-stage unit UB are integrated into an intermediate storage tank 12. That is, the intermediate storage tank 12 is arranged between multiple reverse osmosis membrane devices 6A and 6B. The intermediate storage tank 12 stores permeated water from the reverse osmosis membrane device 6A located upstream of the intermediate storage tank 12 and delivers the permeated water to the reverse osmosis membrane device 6B located downstream of the intermediate storage tank 12. The water level of the intermediate storage tank 12 is measured by a third water level gauge 13 (means for measuring a concentration correlation parameter) provided in the intermediate storage tank 12. The first-stage unit UA does not have a third valve V3, and the second-stage unit UB does not have a first valve V1.

[0029] The first-stage unit UA and the second-stage unit UB are selectively operated. Figure 5 shows the state in which the first-stage unit UA is operating and the second-stage unit UB is stopped. When the first-stage unit UA is operating, the first valve V1A and the fourth valve V4A are closed, and the second valve V2A is opened. The second to fourth valves V2B, V3, and V4B of the second-stage unit UB are closed (however, the third valve V3 may be open). This prevents water from entering or leaving the first-stage unit UA. By operating the first-stage unit UA, intermediately treated water is stored in the intermediate storage tank 12. The target value for the average boron concentration of the intermediately treated water in the intermediate storage tank 12 is calculated in advance from the boron concentration in the raw water, the discharge standard value, the boron rejection rate of the reverse osmosis membrane device 6A, etc., and operation of the first-stage unit UA is stopped when the average boron concentration reaches the target value. The concentration acquisition means 10A converts the measurement values ​​of the concentration correlation parameter measurement means 8, 13 into boron concentrations in the treated water in the intermediate storage tank 12.

[0030] Next, the second valve V2B of the second-stage unit UB is opened (the third valve V3 is closed if it is open). This ensures that no water flows in or out of the second-stage unit UB with the outside. The second-stage unit UB is then operated in the same manner as the first-stage unit UA. When the average boron concentration in the treated water in the treated water tank 7 reaches the target value, or before that, the operation of the second-stage unit UB is stopped. The concentration acquisition means 10B converts the measurement values ​​of the concentration correlation parameter measurement means 9, 13 into the boron concentration in the treated water in the treated water tank 7. The third valve V3 is then opened, and the treated water is released from the treated water tank 7.

[0031] This modification also has multiple reverse osmosis membrane devices 6A, 6B connected in series, and therefore provides the same effects as the third embodiment. In this modification, raw water can be supplied to the raw water tank 2 of the first-stage unit UA while the second-stage unit UB is in operation, so operation of the first-stage unit UA can be started promptly after switching to the first-stage unit UA. Furthermore, because concentrated water can be removed from the first-stage (second-stage) unit UA (UB) while the second-stage (first-stage) unit UB (UA) is in operation, the removal of concentrated water does not reduce the availability of the water treatment device 1.

[0032] FIG. 6 shows a schematic configuration of a water treatment device 1 according to a second modified example of the third embodiment. The water treatment device 1 of this modified example has two intermediate storage tanks 12A, 12B arranged in series between multiple reverse osmosis membrane devices 6. The upstream intermediate storage tank 12A corresponds to the treated water tank 7 of the first embodiment, and the downstream intermediate storage tank 12B corresponds to the raw water tank 2 of the first embodiment. The upstream intermediate storage tank 12A stores the permeated water from the upstream reverse osmosis membrane device 6A, and the downstream intermediate storage tank 12B delivers the permeated water to the downstream reverse osmosis membrane device 6B. In other words, this modified example also has a configuration in which multiple units UA, UB are arranged in series when the water treatment device 1 of the first embodiment is configured as a single unit.

[0033] The water treatment device 1 of this modification operates similarly to the water treatment device 1 of the first modification. However, by closing the third valve V3A between the upstream intermediate storage tank 12A and the downstream intermediate storage tank 12B, the first-stage unit UA and the second-stage unit UB can be operated simultaneously. When the boron concentration in the treated water in the intermediate storage tank 12A of the first-stage unit UA reaches a predetermined target, operation of the first-stage unit UA is stopped. Then, the third valve V3A is opened, and the treated water is transferred to the intermediate storage tank 12B of the second-stage unit UB. The second-stage unit UB begins operation and treats the treated water stored in the intermediate storage tank 12A of the first-stage unit UA. When the boron concentration in the treated water in the treated water tank 7 of the second-stage unit UB reaches a predetermined target, operation of the second-stage unit UB is stopped. During this time, the first-stage unit UA receives new raw water, starts operation, and treats the new raw water. In this way, the first-stage unit UA and the second-stage unit UB can be operated simultaneously, significantly improving treatment efficiency. It is preferable that the first-stage unit UA and the second-stage unit UB start and stop operation at the same time.

[0034] (Fourth embodiment) FIG. 7 shows a schematic configuration of a water treatment device 1 according to a fourth embodiment of the present invention. The water treatment device 1 of this embodiment is configured by arranging multiple units UA and UB in parallel, where the water treatment device 1 of the first embodiment is a single unit. The first-stage unit UA and the second-stage unit UB each include raw water tanks 2A and 2B, at least one reverse osmosis membrane device 6A and 6B, concentrated water circulation lines L5A and L5B, treated water tanks 7A and 7B, raw water supply lines L1A and L1B, and first valves V1A and V1B provided in the raw water supply lines L1A and L1B. The water treatment device 1 also includes a main raw water supply line L8, which is connected to the supply line L1A of the first-stage unit UA and the raw water supply line L1B of the second-stage unit UB.

[0035] In the water treatment device 1 of this embodiment, the first-stage unit UA and the second-stage unit UB can be operated completely independently. For example, the second-stage unit UB can receive raw water while the first-stage unit UA is operating, and the first-stage unit UA can receive raw water while the second-stage unit UB is operating. This allows the water treatment device 1 as a whole to always receive raw water, enabling essentially continuous treatment. In this case, only one of the first valves V1A and V1B of the multiple units UA and UB is open at a time. Furthermore, if a large amount of raw water is temporarily generated, the first-stage unit UA and the second-stage unit UB can simultaneously receive raw water. In this embodiment, the first-stage unit UA and the second-stage unit UB do not affect each other, allowing for various operating methods to be tailored to the raw water generation situation.

[0036] Although several embodiments of the present invention have been described above, the present invention is not limited to these. For example, the concentrated water can be returned to a raw water tank upstream of the raw water tank 2. This configuration is also possible if the raw water tank is sufficiently large so that returning concentrated water to the raw water tank does not significantly change the boron concentration in the raw water supplied to the raw water tank 2. Furthermore, the first to fourth embodiments (including the first and second modifications) can be combined with each other. For example, the ion exchange device 11 of the second embodiment can be combined with any other embodiment or modification. Individual units UA and UB can be configured as shown in the third embodiment or its modifications (FIGS. 4 to 6), and these units UA and UB can be combined in parallel as shown in the fourth embodiment (FIG. 7). In this case, multiple units UA and UB, each of which has multiple reverse osmosis membrane devices 6A and 6B connected in series, are connected in parallel, thereby enabling highly efficient treatment of raw water with a high boron concentration. [Explanation of symbols]

[0037] 1 Water treatment equipment 2 Raw water tank 6,6A,6B Reverse osmosis membrane equipment 7, 7A, 7B Treated water tank 8,9,8A,8B,9A,9B,13 Measurement methods for concentration correlation parameters 10 Concentration acquisition means 11 Ion exchange device 12, 12A, 12B Intermediate storage tank 13, 13A, 13B heat exchanger L5, L5A, L5B concentrated water circulation line L6 Treated water circulation line L7 Concentrate return line L8 Main raw water supply line V1~V4 valves

Claims

1. A raw water tank for storing raw water containing boron; At least one reverse osmosis membrane device that separates the raw water delivered from the raw water tank into permeate and concentrated water; a concentrated water circulation line that returns the concentrated water to the raw water tank; a treated water tank for storing the permeated water as treated water; a concentration acquisition means for acquiring the concentration of boron in the treated water stored in the treated water tank, A water treatment device, wherein when the concentration acquired by the concentration acquisition means reaches a predetermined value, at least a portion of the treated water stored in the treated water tank is discharged from the treated water tank.

2. The water treatment device according to claim 1 , wherein when the concentration acquired by the concentration acquisition means reaches the predetermined value, at least a portion of the water stored in the raw water tank is discharged from the raw water tank.

3. a measuring means for measuring a concentration correlation parameter that correlates with the concentration of boron in the treated water stored in the treated water tank, The water treatment device described in claim 1 or 2, wherein the concentration acquisition means determines whether the boron concentration of the treated water stored in the treated water tank has reached the predetermined value based on the relationship between the concentration correlation parameter and the average boron concentration in the treated water and the concentration correlation parameter measured by the measuring means, and the relationship is determined in advance from the boron concentration of the raw water, the flow rate of the treated water, and the boron rejection rate of at least one reverse osmosis membrane device.

4. The water treatment device according to claim 3 , wherein the concentration correlation parameter is at least one of the water volume of the raw water tank, the water volume of the treated water tank, and the elapsed time since the start of treatment in the reverse osmosis membrane device.

5. an ion exchange device; a treated water circulation line connecting the treated water tank and the ion exchange device, for circulating the treated water stored in the treated water tank between the tank and the ion exchange device; The water treatment device according to claim 1 , further comprising:

6. The water treatment system of claim 1 , wherein the at least one reverse osmosis membrane device comprises a plurality of reverse osmosis membrane devices connected in series.

7. 7. The water treatment device according to claim 6, further comprising an intermediate storage tank between the plurality of reverse osmosis membrane devices, the intermediate storage tank storing permeated water from the reverse osmosis membrane device upstream of the intermediate storage tank and supplying the permeated water to the reverse osmosis membrane device downstream of the intermediate storage tank.

8. 7. The water treatment device according to claim 6, further comprising two intermediate storage tanks arranged in series between the plurality of reverse osmosis membrane devices, wherein the upstream intermediate storage tank stores permeated water from the reverse osmosis membrane device upstream of the upstream intermediate storage tank, and the downstream intermediate storage tank delivers the permeated water to the reverse osmosis membrane device downstream of the downstream intermediate storage tank.

9. a main supply line for the raw water; a plurality of units each including the raw water tank, the at least one reverse osmosis membrane device, the concentrated water circulation line, the treated water tank, a raw water supply line to the raw water tank, and a valve provided on the supply line; The water treatment device of claim 1 , wherein the main supply line is connected to the supply lines of the plurality of units.

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