Water treatment method and water treatment system

Abstract

To operate water treatment equipment efficiently and suppress the increase in costs associated with obtaining water quality parameters. [Solution] A water treatment method in a water treatment system 1 having a first line L1 through which first water W1 flows, a second line L2 through which second water W2 flows, a confluence (intermediate tank) 33 of the first line L1 and the second line L2, a third line L3 connected to the intermediate tank 33 through which water W3 formed by the confluence of the first water W1 and the second water W2 flows, and a water treatment device 6 provided on the third line L3, comprises acquiring at least one water quality parameter at the inlets P1 and P2 of the intermediate tanks 33 of the first and second waters W1 and W2, acquiring flow rate parameters at the inlets P1 and P2 of the intermediate tanks 33 of the first and second waters W1 and W2, and determining the operating conditions of the water treatment device 6 based on at least one water quality parameter and the flow rate parameter.

Description

Technical Field

[0001] The present invention relates to a water treatment method and a water treatment system.

Background Art

[0002] With the increasing demand for high-quality pure water, various methods for removing impurities contained in pure water have been studied in recent years. Patent Document 1 describes installing a total organic carbon concentration meter (TOC meter) at the inlet of an ultraviolet irradiation device and controlling the output of the ultraviolet irradiation device based on the total organic carbon concentration (TOC concentration) measured by the TOC meter. Patent Document 1 also describes a return pipe that returns a part of the treated water of the ultraviolet irradiation device to the upstream of the ultraviolet irradiation device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the return pipe described in Patent Document 1 is provided, a confluence of two lines occurs upstream of the ultraviolet irradiation device. In order to efficiently control the output of the ultraviolet irradiation device, it is preferable to install the TOC meter between the inlet of the ultraviolet irradiation device, that is, between the confluence and the ultraviolet irradiation device. However, in order to manage the TOC concentration of the water that converges at the confluence, it is preferable to install the TOC meter upstream of the confluence. To achieve these purposes, it is necessary to install TOC meters upstream and downstream of the confluence. This problem also applies to water quality meters other than the TOC meter and water treatment devices other than the ultraviolet irradiation device.

[0005] An object of the present invention is to provide a water treatment method capable of efficiently operating a water treatment device and suppressing an increase in cost for acquiring water quality parameters. [Means for solving the problem]

[0006] The present invention relates to a water treatment method in a water treatment system having a first line through which first water flows, a second line through which second water flows, a confluence of the first line and the second line, a third line connected to the confluence through which water formed by the confluence of the first water and the second water flows, and a water treatment device provided in the third line. The water treatment method of the present invention comprises obtaining at least one water quality parameter at the inlet of the confluence of the first and second waters and a flow rate parameter at the inlet of the confluence of the first and second waters, and determining the operating conditions of the water treatment device based on at least one water quality parameter and a flow rate parameter. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a water treatment method that enables efficient operation of a water treatment device and suppresses the increase in costs for obtaining water quality parameters. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of a water treatment device according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of the water treatment apparatus according to the comparative example. [Figure 3] This is a conceptual diagram showing the time evolution of the TOC concentration in the intermediate tank. [Figure 4] This is a schematic diagram of the water treatment apparatus according to the embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the water treatment method and water treatment system of the present invention will be described below with reference to the drawings. Figure 1 shows a schematic configuration of a water treatment system 1 according to one embodiment of the present invention. The water treatment system 1 has an upstream pretreatment device 2 and a downstream pure water production device (primary system) 3. The water treatment system 1, together with a downstream subsystem (secondary system) 4, constitutes an ultrapure water production device. The water to be treated after being treated in subsystem 4 is supplied to a use point 5. The raw water supplied to the pretreatment device 2 contains dissolved oxygen and organic matter. In the following description, upstream and downstream are defined with respect to the water flow direction D in the first line L1 and the third line L3. "Adjustment" includes both the automatic control of various operating parameters (on / off of the device, flow rate, pressure, valve opening / closing, power consumption, etc.) by a control device and the manual adjustment of these operating parameters by an operator. The present invention can be applied not only to the water treatment system 1 but also to subsystem 4.

[0010] (Configuration of the pure water production system 3) The pretreatment device 2 includes a filter 21 for removing dust and other particles with relatively large particle sizes, and an activated carbon tower 22 for removing impurities such as high-molecular-weight organic substances and oxidizing agents. For example, a sand filter can be used as the filter 21. The configuration of the pretreatment device 2 is not limited to this and may include a deaeration device, a reverse osmosis membrane device, etc. The pure water production device 3 includes an ion removal device 31, a reverse osmosis membrane device 32, an intermediate tank 33, a first deoxygenation device 34, an ultraviolet irradiation device 35, an ion exchanger filling device 36, and a second deoxygenation device 37. Each device and tank 31 to 37 are arranged in series in this order on the main pipe L4 from upstream to downstream with respect to the flow direction D of the water to be treated. At the branching point P3 downstream of the second deoxygenation device 37, the return pipe L2 branches off from the main pipe L4 and joins the intermediate tank 33. Although not shown in the diagram, in addition to the intermediate tank 33, tanks may be provided to store the treated water from each of the pretreatment devices 2 and the pure water production device 3, such as the activated carbon tower 22 and the ion removal device 31. Although not shown in the diagram, in addition to the return pipe L2, a line may be provided to return a portion of the treated water from any of the devices in the pure water production device 3 to an upstream tank or the like.

[0011] In the following explanation, the portion of the main pipe L4 from the pretreatment device 2 to the intermediate tank 33 is referred to as the first line L1, the return pipe L2 is referred to as the second line L2, and the portion of the main pipe L4 from the intermediate tank 33 to the subsystem 4 is referred to as the third line L3. The first line L1 and the second line L2 merge at the junction 33. The ultraviolet irradiation device 35 is sometimes referred to as the water treatment device 6. Therefore, the third line L3 is connected to the junction 33 of the first line L1 and the second line L2, the water treatment device 6 is located downstream of the junction 33 in the flow direction D of the third line L3, and the second line L2 branches off from the third line L3 downstream of the water treatment device 6 in the flow direction D and merges at the junction 33. The junction 33 is the intermediate tank 33, but the intermediate tank 33 can be omitted and the connections made via piping can be made instead. However, the intermediate tank 33 has the function of continuing the operation of the pure water production device 3 and subsystem 4 for a certain period of time even when the pretreatment device 2 etc. is temporarily stopped, thereby ensuring the supply of ultrapure water to the use point 5, so it is preferable to install the intermediate tank 33. In the following explanation, the confluence section 33 will be referred to as the intermediate tank 33. The water flowing through the first line L1 will be called the first water W1, the water flowing through the second line L2 will be called the second water W2, and the water flowing through the third line L3 will be called the third water W3. The third water W3 is the water formed by the confluence of the first water W1 and the second water W2.

[0012] The ion removal device 31 includes a cation tower (not shown) filled with cation exchange resin, a decarbonation tower (not shown), and an anion tower (not shown) filled with anion exchange resin, which are arranged in series in this order from upstream to downstream. Instead of the ion removal device 31, it is also possible to arrange a water softening device that removes hardness components such as calcium and magnesium upstream and an electrodeionized water generator (EDI) in series downstream. The EDI removes ionic components that inhibit the organic matter decomposition treatment in the ultraviolet irradiation device 35. The reverse osmosis membrane device 32 removes impurities such as ions. In this embodiment, since the ion removal device 31 is provided upstream of the reverse osmosis membrane device 32, the reverse osmosis membrane device 32 mainly removes uncharged substances such as organic matter. The reverse osmosis membrane device 32 may be provided in multiple stages. The treated water from the reverse osmosis membrane device 32 is stored in an intermediate tank 33.

[0013] The first deoxygenation device 34 removes oxygen from the water to be treated, thereby reducing the dissolved oxygen concentration in the water. Since the first deoxygenation device 34 is located upstream of the ultraviolet irradiation device 35, the ultraviolet irradiation device 35 is supplied with water to be treated that has a reduced (adjusted) dissolved oxygen concentration. The type of the first deoxygenation device 34 is not limited as long as it can remove dissolved oxygen; for example, a vacuum degasser can be used. Generally, in a vacuum degasser, a gas-liquid contact material to increase the surface area of ​​the water is filled into the degasser, the gas pressure inside the degasser is reduced by a vacuum pump, the water to be treated is placed under vacuum, and dissolved oxygen is removed. The dissolved oxygen concentration can be adjusted by adjusting the vacuum level inside the degasser using a vacuum pump. The vacuum level can be adjusted using an inverter connected to the vacuum pump.

[0014] As the first deoxygenation device 34, a nitrogen degasser can be used to improve degassing performance by introducing nitrogen. The dissolved oxygen concentration can be adjusted by adjusting the vacuum level and the nitrogen inflow rate (sweep gas amount). A degassing membrane device may also be used as the first deoxygenation device 34. In this case as well, a vacuum pump is used, similar to the vacuum degasser, and the dissolved oxygen concentration can be adjusted by adjusting the vacuum level. The vacuum level can be adjusted using an inverter connected to the vacuum pump. Vacuum degassers, nitrogen degassers, and membrane degassers can reduce the dissolved oxygen concentration in water while simultaneously transferring volatile organic compounds and carbon dioxide into the gas phase, thereby reducing their concentrations in water. The first deoxygenation device 34 described above may be a single-stage configuration or a multi-stage configuration in which multiple devices are connected in series.

[0015] The ultraviolet irradiation device 35 irradiates the water to be treated with ultraviolet light to decompose organic matter contained in the water. As the ultraviolet irradiation device 35, for example, an ultraviolet irradiation device 35 that generates ultraviolet light with a wavelength of at least one of 185 nm and 254 nm (for example, a low-pressure ultraviolet irradiation device) can be used. The amount of ultraviolet irradiation is the irradiation energy added per unit volume of water (unit: kWh / m³). 3 Since it is defined as ), the irradiation dose can be adjusted by changing the number of lamps on the ultraviolet irradiation device 35 and by adjusting the brightness, as well as by changing the flow rate of the water to be treated.

[0016] The ion exchanger packing device 36 removes organic decomposition products generated in the treated water of the ultraviolet irradiation device 35 by irradiation with ultraviolet light. The ion exchanger packing device 36 is filled with ion exchange resin, but monolithic or fibrous ion exchangers may also be filled. The ion exchanger packing device 36 may also be an EDI filled with ion exchange resin. Since the EDI is a continuous regeneration type, a regeneration process for the ion exchange resin is unnecessary.

[0017] The second deoxygenation device 37 is located downstream of the ion exchanger filling device 36 and can have the same configuration as the first deoxygenation device 34. The second deoxygenation device 37 removes dissolved oxygen, carbon dioxide, etc. from the water to be treated.

[0018] The treated water of the second deoxygenation device 37 is sent to the subsystem 4. A second line L2 that branches downstream of the second deoxygenation device 37 adjusts the flow rate of the pure water supplied to the subsystem 4. For this purpose, a valve V1 for adjusting the flow rate or pressure is arranged in the second line L2. Since it is preferable that the second line L2 branches at the most downstream of the pure water production device 3, it branches from a third line L3 downstream of the second deoxygenation device 37, but another branch line that branches from the third line L3 upstream of the second deoxygenation device 37 may be provided.

[0019] (Acquisition of water quality parameters and flow rate parameters) In order to reduce the TOC concentration while operating the ultraviolet irradiation device 35 at an appropriate ultraviolet irradiation amount, it is necessary to appropriately set the operating conditions of the ultraviolet irradiation device 35. One of the operating conditions is the ultraviolet irradiation amount. Since the appropriate ultraviolet irradiation amount depends on the water quality of the water to be treated, the water quality of the water to be treated by the ultraviolet irradiation device 35 is also one of the operating conditions. Since the ultraviolet irradiation device 35 is a device for reducing the TOC concentration, in order to appropriately set the operating conditions of the ultraviolet irradiation device 35, it is desirable to obtain the TOC concentration at the inlet P4 of the ultraviolet irradiation device 35, in this embodiment, between the first deoxygenation device 34 and the ultraviolet irradiation device 35. In addition, since dissolved oxygen has the property of absorbing ultraviolet rays, generally, if the dissolved oxygen concentration (DO concentration) is reduced, the absorption of ultraviolet rays is suppressed, and the TOC concentration reduction rate increases (the TOC concentration decreases). Therefore, in order to appropriately set the operating conditions of the ultraviolet irradiation device 35, it is desirable to obtain the DO concentration at the inlet P5 of the first deoxygenation device 34, in this embodiment, between the intermediate tank 33 and the first deoxygenation device 34.

[0020] In this embodiment, a first TOC concentration meter 61 for measuring the total organic carbon (TOC) concentration T1 and a first dissolved oxygen concentration meter (first DO concentration meter) 71 for measuring the DO concentration D1 are provided between the reverse osmosis membrane device 32 and the intermediate tank 33 of the first line L1 (at the inlet P1 of the confluence 33 of the first line L1). A second TOC concentration meter 62 for measuring the TOC concentration T2 and a second dissolved oxygen concentration meter (second DO concentration meter) 72 for measuring the DO concentration D2 are provided between the branching point P3 of the second line L2 of the third line L3 and the subsystem 4. The measured values ​​of the second TOC concentration meter 62 and the measured values ​​of the second DO concentration meter 72 can be considered to be the same as the measured values ​​at the inlet P2 of the intermediate tank 33 (confluence 33) of the second line L2. A first flow meter 81 for measuring flow rate F1 is provided between the reverse osmosis membrane device 32 and the intermediate tank 33 of the first line L1 (at the inlet P1 of the confluence 33 of the first line L1), and a second flow meter 82 for measuring flow rate F2 is provided in the second line L2.

[0021] TOC concentration and DO concentration are examples of water quality parameters at the inlets P1 and P2 of the intermediate tank 33 for the first and second waters W1 and W2. The first and second TOC concentration meters 61 and 62 and the first and second DO concentration meters 71 and 72 are examples of water quality parameter acquisition units 61, 62, 71, and 72 that acquire water quality parameters at the inlets P1 and P2 of the intermediate tank 33 for the first and second waters W1 and W2. Flow rate is an example of a flow rate parameter, and the first and second flow meters 81 and 82 are examples of flow rate parameter acquisition units 81 and 82 that acquire flow rate parameters at the inlets P1 and P2 of the intermediate tank 33 for the first and second waters W1 and W2. In this embodiment, the TOC concentration and DO concentration at the inlets P1 and P2 of the intermediate tank 33 for the first and second waters W1 and W2 are obtained as water quality parameters, and the flow rates at the inlets P1 and P2 of the intermediate tank 33 for the first and second waters W1 and W2 are obtained as flow rate parameters.

[0022] The first and second TOC concentration meters 61 and 62, the first and second DO concentration meters 71 and 72, and the first and second flow meters 81 and 82 are connected to the control unit 7. The control unit 7 determines the operating conditions of the ultraviolet irradiation device 35 (water treatment device 6) based on at least one water quality parameter acquired by the water quality parameter acquisition units 61, 62, 71, and 72, and the flow rate parameters acquired by the flow rate parameter acquisition units 81 and 82. The control unit 7 is an example of an operating condition determination unit. Specifically, the control unit 7 determines the TOC concentration T3 of the water W3 at the inlet P4 of the ultraviolet irradiation device 35 as follows, based on the TOC concentrations T1 and T2 and the flow rates F1 and F2. T3=(T1×F1+T2×F2) / (F1+F2) Formula (1) Similarly, the control unit 7 determines the DO concentration D3 of the water W3 at the inlet P5 of the first deoxygenation device 34 based on the DO concentrations D1 and D2 and the flow rates F1 and F2 as follows. D3 = (D1 × F1 + D2 × F2) / (F1 + F2) Equation (2) Instead of the control unit 7 automatically determining the TOC concentration T3 and DO concentration D3, the operator may determine the TOC concentration T3 and DO concentration D3 from the TOC concentrations T1 and T2, the DO concentrations D1 and D2, and the flow rates F1 and F2. Strictly speaking, equation (1) calculates the TOC concentration of water W3 at the inlet P5 of the first deoxygenation device 34, but since the TOC concentration hardly changes with the first deoxygenation device 34, the TOC concentration calculated by equation (1) can be considered as the TOC concentration T3 of water W3 at the inlet P4 of the ultraviolet irradiation device 35.

[0023] Figure 2(a) shows a schematic configuration of the water treatment system 101 of the first comparative example. In the first comparative example, the instruments are provided in the same way as in the embodiment, but the means (control unit 7) for calculating the TOC concentration T3 and DO concentration D3 is not provided. In the first comparative example, the amount of ultraviolet irradiation from the ultraviolet irradiation device 35 is adjusted based on the TOC concentration T1 and DO concentration D1. However, because the TOC concentration is reduced in the ion exchange packing device 36, the TOC concentration T2 at the inlet P2 of the second line L2 is lower than the TOC concentration T1 at the inlet P1 of the confluence 33 of the first line L1. Since the second water W2 with a lower TOC concentration is supplied to the intermediate tank 33 through the second line L2, the first water W1 is diluted with the second water W2 in the intermediate tank 33. As a result, the TOC concentration of the water stored in the intermediate tank 33 becomes lower than the TOC concentration T1. Since the amount of ultraviolet irradiation is determined based on the TOC concentration T1 and DO concentration D1, ultraviolet irradiation is performed at a higher dose than the required dose. As a result, this can easily lead to increased operating costs and a reduced lifespan for the ultraviolet irradiation device 35.

[0024] Figure 2(b) shows a schematic configuration of the water treatment system 201 of the second comparative example. In addition to the first comparative example, a third TOC concentration meter 63 and a third DO concentration meter 73 are installed at the inlet P5 of the first deoxygenation device 34, and the amount of ultraviolet irradiation from the ultraviolet irradiation device 35 is adjusted based on the measurement results of the third TOC concentration meter 63 and the third DO concentration meter 73. Although the problem in the first comparative example does not occur because ultraviolet is irradiated at an appropriate amount, there is a cost for installing the third TOC concentration meter 63 and the third DO concentration meter 73. It is conceivable to move the first TOC concentration meter 61 and the first DO concentration meter 71 to the positions of the third TOC concentration meter 63 and the third DO concentration meter 73, but since the first TOC concentration meter 61 and the first DO concentration meter 71 are originally installed to ensure the performance of the upstream devices, moving them may be difficult. Furthermore, because the distance between the third TOC concentration meter 63 and the third DO concentration meter 73 and the ultraviolet irradiation device 35 is short, there is a possibility that adjustments to the ultraviolet irradiation dose and dissolved oxygen reduction rate may not be made in time when the measurement results of the third TOC concentration meter 63 and the third DO concentration meter 73 fluctuate. For example, if the measured value of the third TOC concentration meter 63 increases, the ultraviolet irradiation dose may become insufficient, potentially increasing the TOC concentration of the treated water from the ultraviolet irradiation device 35. If the measured value of the third TOC concentration meter 63 decreases, there is a possibility that ultraviolet irradiation may be performed with an excessive dose.

[0025] In this embodiment, the TOC concentration T3 and DO concentration D3 are calculated based on the measurement results of the first and second TOC concentration meters 61 and 62, the first and second DO concentration meters 71 and 72, and the first and second flow meters 81 and 82. Therefore, the TOC concentration at the inlet P4 of the ultraviolet irradiation device 35 and the DO concentration at the inlet P5 of the first deoxygenation device 34 can be determined with higher accuracy than in the first comparative example. Furthermore, there is no need to provide a third TOC concentration meter 63 and a third DO concentration meter 73 as in the second comparative example.

[0026] Furthermore, in this embodiment, since the TOC concentrations T1, T2 and flow rates F1, F2 are measured at the inlets P1 and P2 of the intermediate tank 33, changes in the TOC concentration at inlet P4 can be detected more quickly. Similarly, since the DO concentrations D1, D2 and flow rates F1, F2 are measured at the inlets P1 and P2 of the intermediate tank 33, changes in the DO concentration at inlet P5 can be detected more quickly. For example, if the TOC concentration T1 at inlet P1 increases, the actual TOC concentration at inlet P4 will be smaller than T3 calculated by equation (1) until the stored water in the intermediate tank 33 is completely replaced, making it difficult to detect changes in TOC concentration. This is because the intermediate tank 33 functions as a kind of buffer, slowing down changes in water quality downstream of the intermediate tank 33. In this embodiment, changes in TOC concentration T1 can be detected quickly, which provides time to control the amount of ultraviolet irradiation and the dissolved oxygen reduction rate. Therefore, the possibility of a temporary increase in the TOC concentration of the treated water from the ultraviolet irradiation device 35 is reduced.

[0027] (Control of the ultraviolet irradiation device 35 and the first deoxygenation device 34) The control unit 7 controls the ultraviolet irradiation dose of the ultraviolet irradiation device 35 and the dissolved oxygen reduction rate of the first deoxygenation device 34 based on the calculated TOC concentration T3 and DO concentration D3. It is preferable to set a target value for the TOC concentration reduction rate in order to control the ultraviolet irradiation dose and the dissolved oxygen reduction rate. The relationship between TOC concentration T3, DO concentration D3, the ultraviolet irradiation dose of the ultraviolet irradiation device 35 and the TOC concentration reduction rate, and the dissolved oxygen reduction rate of the first deoxygenation device 34 can be obtained experimentally in advance, and this relationship can be stored as data in the control unit 7. Therefore, by calculating the TOC concentration T3 and DO concentration D3 using the method described above and providing a target value for the TOC concentration reduction rate, the control unit 7 can set the ultraviolet irradiation dose and the dissolved oxygen reduction rate, and control the ultraviolet irradiation device 35 and the first deoxygenation device 34. Note that, as will be described later, there is not just one appropriate combination of ultraviolet irradiation dose and dissolved oxygen reduction rate, but several combinations are possible.

[0028] According to this embodiment, the ultraviolet irradiation dose and dissolved oxygen reduction rate can be adjusted more appropriately compared to the first comparative example. Furthermore, since the TOC concentration, DO concentration, and flow rate are measured upstream of the intermediate tank 33, changes in TOC concentration T3 and DO concentration D3 can be detected more quickly when the TOC concentration, DO concentration, or flow rate changes. This also allows the control unit 7 to appropriately set the ultraviolet irradiation dose and dissolved oxygen reduction rate. For example, the flow rate of the second line L2 may be adjusted by valve V1 to adjust the amount of pure water supplied to subsystem 4 in response to fluctuations in the amount of ultrapure water used at use point 5. Since the TOC concentration, DO concentration, and flow rate can be measured continuously, the ultraviolet irradiation dose and dissolved oxygen reduction rate can be quickly adjusted even when the TOC concentrations T1, T2, DO concentrations D1, D2, and flow rates F1, F2 fluctuate.

[0029] Some examples of control methods are described below. If the TOC concentration T3 is higher than the specified value, or if the DO concentration D3 is higher than the specified value, the ultraviolet irradiation dose can be increased, or the rotation speed of the vacuum pump of the first deoxygenation unit 34 can be increased using the inverter described above to increase the dissolved oxygen reduction rate. If the TOC concentration T3 is lower than the specified value, or if the DO concentration D3 is lower than the specified value, the ultraviolet irradiation dose can be decreased, or the rotation speed of the vacuum pump of the first deoxygenation unit 34 can be decreased to decrease the dissolved oxygen reduction rate. The specified values ​​can be set from the data showing the relationship between the TOC concentration T3, DO concentration D3, the ultraviolet irradiation dose of the ultraviolet irradiation unit 35 and the TOC concentration reduction rate, and the dissolved oxygen reduction rate of the first deoxygenation unit 34 as described above.

[0030] The ultraviolet irradiation dose and the dissolved oxygen reduction rate may be adjusted together, or only one of them may be adjusted. Specifically, it is possible to keep the dissolved oxygen reduction rate constant and adjust only the ultraviolet irradiation dose, in which case only the ultraviolet irradiation device 35 needs to be controlled. Conversely, it is also possible to keep the ultraviolet irradiation dose constant and adjust only the dissolved oxygen reduction rate, in which case only the first deoxygenation device 34 needs to be controlled. The choice of whether to adjust the ultraviolet irradiation dose or the dissolved oxygen reduction rate is arbitrary, but for example, a method that consumes less power can be prioritized.

[0031] (modified version) The embodiments described above can be modified in various ways. For example, the flow rate parameter may be the flow rate ratio at the inlets P1 and P2 of the intermediate tanks 33 for the first and second water W1 and W2. In this case, the control unit 7 can determine the TOC concentration T3 based on the TOC concentrations T1 and T2 and the flow rate ratio of the flow rates measured by the first and second flow meters 81 and 82 (let's assume the flow rate measured by the first flow meter 81 : the flow rate measured by the second flow meter 82 = f1:f2), as follows. T3=(T1×f1+T2×f2) / (f1+f2) Equation (3) Similarly, the control unit 7 can determine the DO concentration D3 based on the DO concentrations D1 and D2 and the flow rate ratio f1:f2 of the flow rates measured by the first and second flow meters 81 and 82, as follows. D3 = (D1 × f1 + D2 × f2) / (f1 + f2) Equation (4) Therefore, in this modified example, the control unit 7 can adjust at least one of the ultraviolet irradiation dose and the dissolved oxygen reduction rate based on at least one of the TOC concentrations T1, T2 and DO concentrations D1, D2 at the inlets P1, P2 of the intermediate tanks 33 of the first and second water W1, W2, and the flow rate ratio f1:f2.

[0032] Instead of directly measuring the TOC concentrations T1 and T2 and the DO concentrations D1 and D2 with the first and second TOC meters and the first and second DO meters, they may be calculated from the removal performance of the upstream water treatment equipment. For example, if a TOC concentration meter and a DO concentration meter are installed between the pretreatment equipment 2 and the ion removal equipment 31, the TOC concentration T1 and DO concentration D1 can be calculated from the combined TOC concentration reduction rate and the combined DO reduction rate of the ion removal equipment 31 and the reverse osmosis membrane equipment 32. This may allow existing instruments to be utilized and new instruments to be omitted. Also, instead of directly measuring the flow rates F1 and F2 with the first and second flow meters 81 and 82, they may be calculated from the measurements of other flow meters. For example, if the flow rate F3 in the section between the intermediate tank 33 of the third line L3 and the second deoxygenation equipment 37 can be measured with another flow meter, the flow rate F2 can be calculated as F3 - F1. If the flow rate F4 in the section between the branch point P3 of the third line L3 and the second line L2 and subsystem 4 can be measured with an existing flow meter, the flow rate F2 of the second line L2 can be calculated using F3-F4. Since the flow rate F2 can be calculated from the flow rate F1 of the first line L1 and the flow rates F3 and F4 of the third line L3, the second flow meter 82 can be omitted.

[0033] The TOC concentration T3 and DO concentration D3 can also be calculated by considering the amount of water stored in the intermediate tank 33. Figure 3 shows an example of the time change of the TOC concentration in the intermediate tank 33. For example, if the TOC concentration T2 in the second line L2 starts to increase at time t1 and becomes constant at time t2 (for simplicity, we assume that the TOC concentration T1 is constant), the TOC concentration T3 calculated using equation (1) above will start to increase at time t1, increase in a pattern similar to that of TOC concentration T2, and become constant at time t2. However, since the TOC concentration TT of the water stored in the intermediate tank 33 increases at a lower rate than T3, there is a time lag before the TOC concentration TT reaches the calculated value T3 in equation (1). This time lag TR is given by TR = t3 - t2 = VT / (F1 + F2), where t3 is the time when the TOC concentration TT matches the calculated value T3, VT is the amount of water stored in the intermediate tank 33, F1 is the flow rate of the first line L1, and F2 is the flow rate of the second line L2. If the amount of ultraviolet irradiation is controlled based on the TOC concentration T3 calculated by equation (1) without considering the intermediate tank 33, excessive ultraviolet irradiation will occur between times t1 and t3. Therefore, the actual TOC concentration TT in the intermediate tank 33 may be calculated based on the amount of water stored in the intermediate tank 33 VT, and the amount of ultraviolet irradiation may be adjusted accordingly. The amount of water stored in the intermediate tank 33 VT can be determined, for example, if the intermediate tank 33 is a cylindrical tank, as the product of the measured value of a water level gauge (not shown) installed in the intermediate tank 33 and the cross-sectional area of ​​the intermediate tank 33.

[0034] In addition to TOC concentration and DO concentration, water quality parameters include resistivity, conductivity, ion concentration, and oxidizing agent concentration (e.g., hydrogen peroxide concentration). The water treatment device 6 may be the ion removal device 31, reverse osmosis membrane device 32, first deoxygenation device 34, ion exchanger packing device 36, and second deoxygenation device 37 shown in Figure 1, or it may be an activated carbon device, EDI, etc. For example, with the reverse osmosis membrane device 32, the recovery rate can be adjusted, and with the EDI, the current value and space velocity SV can be adjusted based on the water quality parameters. In this embodiment, the first line L1 and the second line L2 are connected to the intermediate tank 33, but other lines may also merge into the intermediate tank 33. In this case as well, water quality parameters and flow rate parameters at the inlet of the intermediate tank 33 can be obtained for the water flowing through the first and second lines L1 and L2 and the water flowing through the other lines, and the TOC concentration T3 and DO concentration D3 at the inlet P5 of the first deoxygenation device 34 can be calculated from these water quality parameters and flow rate parameters.

[0035] (Example 1, Comparative Example 1) In the apparatus shown in Figure 4(a), raw water adjusted to a TOC concentration of 5 μg / L and an DO concentration of 1000 μg / L was supplied to tank 41, and the water was sequentially passed through the ultraviolet irradiation device 42, the ion exchanger filling device 43, and the degassing membrane device (deoxygenation device) 44, with a portion of the treated water being returned to tank 41. The raw water supply flow rate was 3 m³ 3 The water flow rate for the ultraviolet irradiation device 42, ion exchange packing device 43, and degassing membrane device 44 is 4 m / h. 3 / h, return water flow rate is 1m 3 The flow rate was set to / h. The target TOC concentration for the treated water (point B) was set to 1 μg / L. A flow meter, TOC concentration meter, and DO concentration meter were installed upstream of tank 41 (point A) and downstream of the branch point P3 of the return pipe L2 (point B), and a flow meter was installed in the return pipe L2 (point C). The specifications and conditions of each device are shown below. • UV irradiation device 42: Low-pressure UV oxidation device JPW (manufactured by Nippon Photo Science Co., Ltd.) • Ion exchanger packing apparatus 43: A resin tower filled with a mixed bed of cation exchange resin AMBERJET 1024H (manufactured by Organo Corporation) and anion exchange resin AMBERJET 4002 OH (manufactured by Organo Corporation) in a volume ratio of 1:2. • Space velocity SV of ion exchange packing device 43: 60 ( / h) • TOC concentration meter: M500e (manufactured by VEOLIA) • DO concentration meter: Orbisphere 510 (manufactured by Hach)

[0036] In Example 1, the TOC and DO concentrations at the inlet (point D) of the ultraviolet irradiation device 42 were calculated from the TOC and DO concentrations of the raw water (point A) and treated water (point B), and the flow rate ratio of the raw water (point A) and return water (point C). Specifically, the relationship between the TOC and DO concentrations of the water to be treated by the ultraviolet irradiation device 42 (point D), the ultraviolet irradiation amount, and the TOC concentration reduction rate was determined in advance. In Example 1, the ultraviolet irradiation amount was determined from the calculated TOC and DO concentrations at the inlet (point D) of the ultraviolet irradiation device 42, the target TOC concentration of the treated water (point B), and the above relationship. In Comparative Example 1, the ultraviolet irradiation amount was determined from the measured TOC and DO concentrations of the raw water (point A), the target TOC concentration of the treated water (point B), and the above relationship. The ultraviolet irradiation amount was adjusted by lamp dimming.

[0037] In Example 1, the TOC concentration of the treated water (point B) could be adjusted to a value similar to the target TOC concentration. This indicates that in Example 1, the amount of ultraviolet irradiation could be appropriately adjusted without directly measuring the TOC concentration and DO concentration at the inlet (point D) of the ultraviolet irradiation device 42. In Comparative Example 1, the amount of ultraviolet irradiation was set based on a TOC concentration higher than the actual TOC concentration of the water being treated by the ultraviolet irradiation device 42. As a result, the ultraviolet irradiation was performed at an excessive dose, and the TOC concentration became approximately 0.2 μg / L lower than the target TOC concentration.

[0038] (Example 2, Comparative Example 2) As shown in Figure 4(b), in Example 1 and Comparative Example 1, the flow rate of the raw water was 2 m 3 / h, return water flow rate 2m 3The setting was set to / h. Other conditions were the same as in Example 1 and Comparative Example 1. Example 2 and Comparative Example 2 simulated fluctuations in the flow rate of the return water, but in Example 2, it was found that the amount of ultraviolet irradiation could be appropriately adjusted, similar to Example 1. In Comparative Example 2, the ultraviolet irradiation was at an excessive dose, so the TOC concentration was about 0.4 μg / L lower than the target TOC concentration.

[0039] (Example 3, Comparative Example 3) As shown in Figure 4(c), a degassing membrane device (deoxygenation device) 45 was installed between the tank 41 and the ultraviolet irradiation device 42 (in front of the ultraviolet irradiation device 42). The ultraviolet irradiation dose was 0.11 kWh / m². 3 It was fixed at [value]. In Example 3, the TOC concentration and DO concentration at the inlet (point E) of the degassing membrane device 45 were calculated from the TOC concentration and DO concentration of the raw water (point A) and treated water (point B), and the flow rate ratio of the raw water (point A) and return water (point C). Since the TOC concentration hardly changes with the degassing membrane device 45, the TOC concentration at the inlet (point E) of the degassing membrane device 45 is considered to be approximately the same as the TOC concentration at the inlet (point D) of the ultraviolet irradiation device 42. In Example 3, the DO concentration at the inlet (point E) of the degassing membrane device 45 was determined from the calculated TOC concentration and DO concentration at the inlet (point D) of the ultraviolet irradiation device 42, the target TOC concentration of the treated water (point B), the amount of ultraviolet irradiation, and the above relationship, and the dissolved oxygen removal rate of the degassing membrane device 45 was determined from this. In Comparative Example 3, the dissolved oxygen removal rate of the degassing membrane device 45 was determined from the measured values ​​of TOC concentration and DO concentration of the raw water (point A), the target TOC concentration of the treated water (point B), the amount of ultraviolet irradiation, and the above-mentioned relationship. The inverter setting value was determined from the relationship between the DO concentration and treatment flow rate of the water treated by the degassing membrane device 45, which was obtained in advance, and the inverter setting value of the vacuum pump and the dissolved oxygen removal rate.

[0040] In Example 3, the TOC concentration of the treated water (point B) could be adjusted to a value similar to the target TOC concentration. This shows that in Example 3, the dissolved oxygen removal rate can be appropriately adjusted without directly measuring the TOC concentration and DO concentration at the inlet (point E) of the degassing membrane device 45. In Comparative Example 3, the dissolved oxygen removal rate was set based on a TOC concentration higher than the actual TOC concentration of the treated water in the ultraviolet irradiation device 42. As a result, the amount of ultraviolet light absorbed by dissolved oxygen decreased, and the TOC concentration became about 0.4 μg / L lower than the target TOC concentration. [Explanation of Symbols]

[0041] 1. Water treatment system 7 Control Unit 33 Intermediate tank (junction) 34. First deoxygenation unit 35. Ultraviolet irradiation device (water treatment device) 61, 62 First and second TOC concentration meters (water quality parameter acquisition unit) 71, 72 First and second DO concentration meters (water quality parameter acquisition unit) 81, 82 First and second flow meters (flow parameter acquisition unit) L1 First line L2 Second line L3 Third Line

Claims

1. A water treatment method in a water treatment system comprising: a first line through which first water flows; a second line through which second water flows; a junction of the first line and the second line; a third line connected to the junction through which water formed by the merging of the first water and the second water flows; and a water treatment device provided in the third line, wherein To obtain at least one water quality parameter at the inlet of the confluence of the first and second waters, and a flow rate parameter at the inlet of the confluence of the first and second waters, A water treatment method comprising determining the operating conditions of the water treatment device based on the at least one water quality parameter and the flow rate parameter.

2. The water treatment method according to claim 1, wherein the aforementioned confluence is a tank.

3. The water treatment method according to claim 1, wherein the at least one water quality parameter is at least one of the total organic carbon concentration and the dissolved oxygen concentration.

4. The water treatment device is an ultraviolet irradiation device, The water treatment method according to claim 1, wherein determining the operating conditions includes adjusting at least one of the ultraviolet irradiation amount of the ultraviolet irradiation device and the dissolved oxygen concentration of the water at the inlet of the ultraviolet irradiation device.

5. The water treatment method according to claim 1, wherein the second line branches off from the third line downstream of the water treatment device and merges with the confluence.

6. The water treatment device is an ultraviolet irradiation device, the at least one water quality parameter is at least one of the total organic carbon concentration and the dissolved oxygen concentration at the inlet of the confluence of the first and second waters, and the flow rate parameter is the flow rate at the inlet of the confluence of the first and second waters. The water treatment method according to claim 5, wherein determining the operating conditions includes adjusting the amount of ultraviolet irradiation from the ultraviolet irradiation device and the dissolved oxygen concentration of the water at the inlet of the ultraviolet irradiation device based on at least one of the total organic carbon concentration and the dissolved oxygen concentration and the flow rate.

7. The water treatment method according to any one of claims 4 or 6, wherein a deoxygenation device is provided between the confluence and the ultraviolet irradiation device.

8. The first water supply is distributed through the first line, A second line through which the second water supply flows, The confluence of the first line and the second line, A third line is connected to the aforementioned confluence, through which the water formed by the confluence of the first water and the second water flows, A water treatment device provided in the third line, A water quality parameter acquisition unit that acquires at least one water quality parameter at the inlet of the confluence of the first and second waters, A flow parameter acquisition unit that acquires flow parameter values ​​at the inlet of the confluence of the first and second waters, An operating condition determination unit determines the operating conditions of the water treatment device based on the at least one water quality parameter obtained by the at least one water quality parameter and the flow rate parameter obtained by the flow rate parameter acquisition unit. A water treatment system.

Images