Reverse osmosis membrane water purifier

Abstract

The invention relates to a reverse osmosis membrane water purifier capable of reducing the TDS concentration of the source water and reducing the wastewater flow rate.Reverse osmosis membrane water purifier (100) includes a reverse osmosis membrane module (10), an inlet water line (20) forming a flow path through which water is introduced into the reverse osmosis membrane module (10) and flows through it, a pump (20B) is located at the inlet water line (20) and pressurizes the water introduced into the reverse osmosis membrane module (10), a permeable water line (30) forming a flow path through which permeable water that has permeated through the reverse osmosis membrane (10A) is discharged from the reverse osmosis membrane module (10), a return water line (40) forming a flow path through which permeable water is returned to the upstream side of the pump (20B), an impermeable water line (50) forming a flow path through which impermeable water is discharged from the reverse osmosis membrane module (10) without permeating through the reverse osmosis membrane (10A) and flows through it, and a flow control unit (60) regulates the flow of water through the impermeable water line (50) in the process. The reverse osmosis membrane module (10) is flushed down to a level lower than the flow rate during pure water production.

Description

reverse osmosis water purifier

[0001] The present disclosure relates to a reverse osmosis membrane water purifier.

[0002] Reverse osmosis membrane water purifiers are known. This type of reverse osmosis membrane water purifier includes a reverse osmosis membrane module with a reverse osmosis membrane. The reverse osmosis membrane water purifier processes water introduced into the reverse osmosis membrane module by passing the water through the reverse osmosis membrane to produce purified water. The reverse osmosis membrane removes dissolved solids such as calcium and magnesium dissolved in the water, allowing only the water to pass through. The water that has passed through the reverse osmosis membrane has a reduced total dissolved solids concentration (TDS concentration), which indicates the concentration of dissolved solids, compared to before passing through the reverse osmosis membrane.

[0003] In this type of reverse osmosis membrane water purifier, a phenomenon occurs in which the TDS concentration of the water discharged at the beginning of purified water production (hereinafter also referred to as "initial water") is high. This phenomenon is thought to occur as follows. Specifically, in a reverse osmosis membrane water purifier that has stopped operation after the end of purified water production, water in a state where dissolved solids are concentrated remains upstream of the reverse osmosis membrane. The dissolved solids in this concentrated water gradually permeate the reverse osmosis membrane and dissolve into the water downstream of the reverse osmosis membrane. Therefore, the TDS concentration of the water remaining downstream of the reverse osmosis membrane after purified water production gradually increases over time. It is thought that when purified water production is subsequently started again, the water downstream of the reverse osmosis membrane with an elevated TDS concentration is discharged. This phenomenon is also known as creeping.

[0004] To address this issue, this type of reverse osmosis membrane water purifier performs a so-called flushing process, in which water with concentrated dissolved solids upstream of the reverse osmosis membrane is discharged immediately after the completion of purified water production, and water with a lower dissolved solids concentration is introduced from the water supply passage to replace the discharged water. This reduces the total amount of dissolved solids in the reverse osmosis membrane module, thereby reducing the TDS concentration in the initial water. However, flushing is not effective enough in reducing the TDS concentration in the initial water. Another issue is that flushing results in a large amount of water being discarded as wastewater.

[0005] Patent Document 1 is known as a technology aimed at reducing the TDS concentration of water discharged at the beginning of purified water generation. The reverse osmosis membrane water purifier of Patent Document 1 is equipped with a return flow path. The return flow path returns water that has permeated the reverse osmosis membrane to the upstream side of the reverse osmosis membrane. With this configuration, the reverse osmosis membrane water purifier of Patent Document 1 can perform flushing using water with a lower TDS concentration than the water supplied from the water supply passage. As a result, the reverse osmosis membrane water purifier of Patent Document 1 can reduce the TDS concentration of water retained inside the reverse osmosis membrane module in advance, thereby reducing the TDS concentration of the initial water. Furthermore, in the case of Patent Document 1, compared to a device not equipped with a return flow path, the water that has permeated the reverse osmosis membrane circulates during flushing, thereby reducing the discharge flow rate during flushing.

[0006] Chinese Utility Model No. 212315745

[0007] Thus, there is a demand for a technology that can further reduce the TDS concentration in the initial water and further reduce the wastewater flow rate in a reverse osmosis membrane water purifier.

[0008] The present disclosure aims to provide a reverse osmosis membrane water purifier that can further reduce the TDS concentration of water discharged at the beginning of purified water production and further reduce the wastewater flow rate.

[0009] A reverse osmosis membrane water purifier according to the present disclosure is a reverse osmosis membrane water purifier that produces purified water by processing water to pass through a reverse osmosis membrane, and includes: a reverse osmosis membrane module having a reverse osmosis membrane; an inlet water passage portion that forms a flow path through which water introduced into the reverse osmosis membrane module flows; a pump provided in the inlet water passage portion that pressurizes the water introduced into the reverse osmosis membrane module; a permeate water passage portion that forms a flow path through which permeate that has passed through the reverse osmosis membrane is discharged from the reverse osmosis membrane module; a return water passage portion that forms a flow path through which the permeate discharged from the reverse osmosis membrane module is returned as return permeate to a side of the inlet water passage portion upstream of the pump; The reverse osmosis membrane module is provided with a non-permeated water flow section that forms a flow path through which non-permeated water discharged from the reverse osmosis membrane module flows without passing through the osmosis membrane, and a flow rate adjustment section that adjusts the flow rate of water flowing through the non-permeated water flow section, wherein the inlet water flow section introduces raw water supplied from a water supply source into the reverse osmosis membrane module when producing purified water, and introduces mixed water obtained by mixing the raw water and the return permeated water into the reverse osmosis membrane module when flushing the reverse osmosis membrane module, and the flow rate adjustment section adjusts the flow rate of water flowing through the non-permeated water flow section to a flow rate that is lower than that during purified water production when flushing the reverse osmosis membrane module.

[0010] FIG. 1 is a diagram schematically illustrating a reverse osmosis membrane water purifier according to embodiment 1. FIG. 2 is a time chart for explaining the reverse osmosis membrane water purifier according to embodiment 1. FIG. 3 is a flowchart for explaining the reverse osmosis membrane water purifier according to embodiment 1. FIG. 4 is a graph showing the relationship between the recovery rate during flushing and the peak value of the TDS concentration in the initial water. FIG. 5 is a diagram schematically illustrating a reverse osmosis membrane water purifier used in an experiment. FIG. 6 is a graph showing the results of an experiment, illustrating the relationship between the discharge rate of purified water and the TDS concentration. FIG. 7 is a graph showing the results of an experiment, illustrating the drainage flow rate during flushing.

[0011] A first embodiment of a reverse osmosis membrane water purifier according to the present disclosure will be described with reference to the drawings. The reverse osmosis membrane water purifier according to each of the following embodiments generates purified water by passing water through a reverse osmosis membrane. The water to be treated (hereinafter referred to as raw water) is tap water, which is water supplied from a water supply such as a municipal waterworks. In addition to tap water, other examples of raw water include well water and rainwater.

[0012] <Embodiment 1> As shown in Figure 1, a reverse osmosis membrane water purifier 100 according to Embodiment 1 includes a reverse osmosis membrane module 10, an inlet water flow section 20, a permeate water flow section 30, a return water flow section 40, a non-permeate water flow section 50, a flow rate regulator 60, and a controller 70. The reverse osmosis membrane module 10 has a reverse osmosis membrane 10A. The reverse osmosis membrane module 10 filters raw water using a so-called crossflow system. The reverse osmosis membrane module 10 performs reverse osmosis membrane treatment on the introduced water. Each reverse osmosis membrane module 10 separates the water into permeate, which is water that has passed through the reverse osmosis membrane 10A during the reverse osmosis membrane treatment, and non-permeate, which is water that has not passed through.

[0013] The reverse osmosis membrane module 10 has an inlet 11, a first outlet 12, and a second outlet 13. Water is introduced into the reverse osmosis membrane module 10 through the inlet 11. The reverse osmosis membrane module 10 discharges permeated water from the first outlet 12 and non-permeated water from the second outlet 13. The permeated water discharged through the first outlet 12 has a reduced TDS concentration compared to the water introduced through the inlet 11. The non-permeated water discharged through the second outlet 13 has a higher TDS concentration than the water introduced through the inlet 11.

[0014] The inlet water passage 20 forms a flow path through which water introduced into the reverse osmosis membrane module 10 flows. The upstream side of the inlet water passage 20 is connected to a water supply source (not shown). The downstream end of the inlet water passage 20 is connected to the inlet 11 of the reverse osmosis membrane module 10. The inlet water passage 20 is provided with, in order from the upstream side of the flow path, a prefilter 20A and a pump 20B. The pump 20B applies a pressure equivalent to reverse osmosis pressure to the water introduced into the reverse osmosis membrane module 10. The pump 20B is driven and controlled by the control unit 70. The prefilter 20A is composed of a filter material such as activated carbon. The prefilter 20A removes turbid components such as particulate components and free residual chlorine from the raw water before reverse osmosis membrane processing. This allows the reverse osmosis membrane water purifier 100 to prevent clogging and deterioration of the reverse osmosis membrane 10A.

[0015] The permeate flow section 30 forms a flow path through which permeate discharged from the reverse osmosis membrane module 10 flows. As shown in FIG. 1 , the upstream end of the permeate flow section 30 is connected to the first outlet 12 of the reverse osmosis membrane module 10. The downstream end of the permeate flow section 30 is connected to a water faucet (not shown). The permeate flow section 30 is provided with, in order from the upstream side of the flow path, a check valve 30A, a pressure switch 30B, and a post filter 30C. The check valve 30A prevents backflow from the downstream side to the upstream side of the permeate flow section 30. The pressure switch 30B detects pressure changes of the permeate flowing through the permeate flow section 30. Specifically, the pressure switch 30B detects pressure changes caused by opening and closing a water faucet (not shown) downstream of the permeate flow section 30. The pressure switch 30B transmits a signal corresponding to the detection result to the control unit 70.

[0016] Like the prefilter 20A, the postfilter 30C is configured with a filter material such as activated carbon. As shown in FIG. 1 , the postfilter 30C is located downstream of the pressure switch 30B. The postfilter 30C can remove volatile organic compounds (VOCs) and odors from the permeated water. This allows the reverse osmosis membrane water purifier 100 to improve the taste of the permeated water. The permeated water that passes through the postfilter 30C is discharged as purified water from a faucet downstream of the permeate flow section 30.

[0017] The return water passage 40 forms a flow path for returning permeate discharged from the reverse osmosis membrane module 10 to the upstream side as return permeate. As shown in FIG. 1 , the upstream end of the return water passage 40 is connected to the branch point P1 of the permeate water passage 30. The downstream end of the return water passage 40 is connected to the junction P2 of the inlet water passage 20. The return water passage 40 forms a flow path between the branch point P1 and the junction P2. The branch point P1 is located upstream of the check valve 30A in the permeate water passage 30. The junction P2 is located upstream of the pump 20B in the inlet water passage 20. The return water passage 40 is provided with, from the upstream side (the branch point P1 side), an on-off valve 40A and a check valve 40B. The on-off valve 40A is closed during purified water production and opened during flushing of the reverse osmosis membrane module 10. In this embodiment, the on-off valve 40A is an electrically operated valve driven by an actuator such as a solenoid or a motor. The on-off valve 40A is controlled by the control unit 70. The check valve 40B prevents backflow from the downstream side to the upstream side in the return water passage section 40.

[0018] The non-permeate water flow section 50 forms a flow path through which non-permeate water discharged from the reverse osmosis membrane module 10 flows. As shown in Figure 1, the upstream end of the non-permeate water flow section 50 is connected to the second outlet 13 of the reverse osmosis membrane module 10. The downstream end of the non-permeate water flow section 50 is open. The non-permeate water that has flowed through the non-permeate water flow section 50 is discharged as wastewater from the downstream end of the non-permeate water flow section 50.

[0019] In the present embodiment, the non-permeated water flow section 50, as shown in FIG. 1 , has a first flow path 51 and a second flow path 52. The first flow path 51 and the second flow path 52 are formed in parallel downstream of the connection portion of the non-permeated water flow section 50 with the second outlet 13. Non-permeated water flows through the first flow path 51 during purified water production. Non-permeated water flows through the second flow path 52 during flushing of the reverse osmosis membrane module 10. The second flow path 52 can flow non-permeated water at a lower flow rate than the first flow path 51. In this embodiment, the second flow path 52 is provided with a second flow control valve 64, which will be described later. The second flow path 52 flows non-permeated water at a lower flow rate than the first flow path 51. In this embodiment, the flow rate of the non-permeated water flowing through the second flow path 52 can be adjusted by adjusting the second flow control valve 64. As a result, the second flow path 52 flows non-permeated water at a lower flow rate than the flow rate of the non-permeated water when flowing through the first flow path 51.

[0020] The flow rate adjustment unit 60 adjusts the flow rate of water flowing through the non-permeate water flow section 50. As shown in FIG. 1 , the flow rate adjustment unit 60 is provided in the non-permeate water flow section 50. The flow rate adjustment unit 60 adjusts the flow rate of water flowing through the non-permeate water flow section 50 during flushing of the reverse osmosis membrane module 10 to a lower flow rate than during purified water production. In this embodiment, the flow rate adjustment unit 60 includes two selector valves 61, 62 and two flow control valves 63, 64. Of the two selector valves 61, 62, the first selector valve 61 is provided in the first flow path 51, and the second selector valve 62 is provided in the second flow path 52. During purified water production, the first selector valve 61 opens the first flow path 51 and the second selector valve 62 closes the second flow path 52 so that non-permeate water flows through the first flow path 51. The two switching valves 61, 62 are electrically operated valves driven by actuators such as solenoids or motors. The two switching valves 61, 62 are controlled by a controller 70. In the present disclosure, the form of flow path switching by the switching valves is not particularly important. The switching valve may be, for example, a single three-way valve disposed at the branch point between the first flow path and the second flow path.

[0021] Of the two flow rate control valves 63, 64, the first flow rate control valve 63 is provided in the first flow path 51, and the second flow rate control valve 64 is provided in the second flow path 52. The first flow rate control valve 63 is a fixed orifice that adjusts the flow rate of non-permeated water flowing through the first flow path 51 to a constant flow rate. The first flow rate control valve 63 is provided with an orifice diameter large enough that the ratio of the flow rate of non-permeated water to the flow rate of water introduced into the reverse osmosis membrane module 10 during purified water production is approximately 20% to 55%. That is, in the reverse osmosis membrane water purifier 100, the ratio of non-permeated water discharged as wastewater to the amount of water introduced into the reverse osmosis membrane module 10 during purified water production is 20% to 55%. In contrast, the ratio of permeated water discharged as purified water to the amount of water introduced into the reverse osmosis membrane module 10 during purified water production is 45% to 80%.

[0022] The ratio of permeate to the amount of water introduced into the reverse osmosis membrane module is generally referred to as the recovery rate. The same meaning applies to recovery rate in this disclosure. Similarly, in this disclosure, the ratio of permeate to the amount of water introduced into the reverse osmosis membrane module is also referred to as the recovery rate. The ratio of non-permeate to the amount of water introduced into the reverse osmosis membrane module is also referred to as the reject rate.

[0023] The second flow control valve 64 adjusts the flow rate of the non-permeated water flowing through the second flow path 52. In this embodiment, the second flow control valve 64 can freely adjust the flow rate of the non-permeated water flowing through the second flow path 52. Specifically, the second flow control valve 64 adjusts the flow rate of the water flowing through the second flow path 52 so that the ratio of the flow rate of the non-permeated water to the flow rate of the water introduced into the reverse osmosis membrane module 10 during flushing of the reverse osmosis membrane module 10 is a predetermined ratio. In this embodiment, the second flow control valve 64 adjusts the ratio of the flow rate of the non-permeated water to the flow rate of the water (mixed water) introduced into the reverse osmosis membrane module 10 during flushing of the reverse osmosis membrane module 10 to 15% or more and 25% or less, specifically, approximately 20%. By adjusting the flow rate of the non-permeated water during flushing of the reverse osmosis membrane module 10 in this manner, the flow rate adjuster 60 makes the flow rate of the non-permeated water discharged as wastewater during flushing less than the flow rate of the non-permeated water discharged as wastewater during purified water production. The second flow rate adjusting valve 64 may be a fixed orifice, similar to the first flow rate adjusting valve 63 .

[0024] In this disclosure, flushing of a reverse osmosis membrane module is defined as driving a pump to introduce water into the reverse osmosis membrane module in a state in which permeated water is not discharged to the outside as purified water and only non-permeated water can be discharged to the outside as wastewater.

[0025] The control unit 70 controls each part of the reverse osmosis membrane water purifier 100. The control unit 70 is mainly composed of, for example, a microcontroller and includes an arithmetic device such as a CPU (Central Processing Unit), and storage means such as RAM and ROM. The control unit 70 is connected to each of the pump 20B, the pressure switch 30B, the on-off valve 40A, and the switching valves 61 and 62. The control unit 70 drives each part in accordance with a program stored in advance in storage means (not shown) or the like, and controls the operation of the reverse osmosis membrane water purifier 100.

[0026] The operation of the reverse osmosis membrane water purifier 100 configured as described above will be described with reference to Figures 2 and 3, etc. Figure 2 shows a time chart of the operation of each part of the reverse osmosis membrane water purifier 100, and Figure 3 shows a flowchart of the control of each part of the reverse osmosis membrane water purifier 100 by the control unit 70. Before the reverse osmosis membrane water purifier 100 starts producing purified water, a water faucet (not shown) downstream of the permeate water flow unit 30 is closed. This state before the start of purified water production is the state before time T1 shown in Figure 2. In this state before the start of purified water production, each part of the reverse osmosis membrane water purifier 100 is in the following states, as shown in Figure 2: the pump 20B is stopped, the on-off valve 40A is closed, the first selector valve 61 is open, and the second selector valve 62 is closed.

[0027] When producing purified water in the reverse osmosis membrane water purifier 100, a water faucet (not shown) downstream of the permeate water passage unit 30 is opened. In the reverse osmosis membrane water purifier 100, when a user or the like opens a water faucet (not shown) at time T1 shown in FIG. 2 , the pressure switch 30B detects the resulting pressure change in the flow path of the permeate water passage unit 30. The pressure switch 30B transmits a signal (ON signal) to the control unit 70 indicating the pressure change caused by the opening of the closed water faucet. As shown in FIG. 3 , the control unit 70 waits for the transmission of an ON signal from the pressure switch 30B in step S110. Upon receiving the ON signal from the pressure switch 30B, the control unit 70 starts driving the pump 20B in step S120.

[0028] When the pump 20B starts operating, raw water supplied from a water supply source (not shown) flows into the pump 20B via the prefilter 20A. The raw water that flows into the pump 20B is pressurized by the pump 20B and introduced into the reverse osmosis membrane module 10 through the inlet 11. Within the reverse osmosis membrane module 10, the raw water is separated into permeated water that has permeated the reverse osmosis membrane 10A and non-permeated water that has not permeated the reverse osmosis membrane 10A. The separated permeated water and non-permeated water are discharged to the outside of the reverse osmosis membrane module 10 through the first outlet 12 and the second outlet 13, respectively. The permeated water discharged from the first outlet 12 flows through the permeated water flow section 30, passes through the post-filter 30C, and flows downstream to be discharged as purified water from a faucet (not shown).

[0029] On the other hand, the non-permeated water discharged from the second outlet 13 of the reverse osmosis membrane module 10 flows through the non-permeated water flow section 50 and is discharged as wastewater from the downstream end of the non-permeated water flow section 50. At this time, in the non-permeated water flow section 50, of the two selector valves 61, 62 serving as the flow rate adjustment section 60, the first selector valve 61 provided in the first flow path 51 is opened, and the second selector valve 62 provided in the second flow path 52 is closed. As a result, the non-permeated water discharged from the second outlet 13 flows through the first flow path 51 of the non-permeated water flow section 50 and is discharged.

[0030] Thereafter, when the user of the reverse osmosis membrane water purifier 100 closes a water faucet (not shown) after the desired amount of purified water has been discharged, the discharge of purified water from the faucet stops. At time T2 shown in FIG. 2 , the user closes the open water faucet (not shown) again, causing a resulting pressure change in the flow path of the permeate water flow section 30, which is detected by the pressure switch 30B. The pressure switch 30B transmits a signal (OFF signal) to the control unit 70 indicating the pressure change caused by the closure of the open water faucet. At this time, the control unit 70 is in a state of waiting for an OFF signal from the pressure switch 30B in step S130, as shown in FIG. 3 . Upon receiving the OFF signal from the pressure switch 30B, the control unit 70 begins flushing of the reverse osmosis membrane module 10.

[0031] Specifically, when flushing the reverse osmosis membrane module 10, the control unit 70 starts a countdown using a timer (step S140). The countdown time can be set as desired to perform flushing. Upon starting the countdown, the control unit 70 executes drive control to open the on-off valve 40A, close the first selector valve 61, and open the second selector valve 62 (step S150). At this time, the pump 20B, which started driving when purified water production began, remains driven.

[0032] Thereafter, when the countdown ends at time T3 (step S160), which is an arbitrarily set time after time T2, the control unit 70 ends the flushing of the reverse osmosis membrane module 10. Specifically, the control unit 70 executes drive control to return the on-off valve 40A to the closed state, the first selector valve 61 to the open state, and the second selector valve 62 to the closed state, and stops the drive of the pump 20B (step S170).

[0033] When flushing the reverse osmosis membrane module 10, the reverse osmosis membrane water purifier 100 continues to drive the pump 20B that was driven when producing purified water. Therefore, in the inlet water flow section 20, raw water flows into the pump 20B via the prefilter 20A, just as when producing purified water. The raw water that flows into the pump 20B is pumped and introduced into the reverse osmosis membrane module 10, where it is treated by the reverse osmosis membrane.

[0034] During flushing of the reverse osmosis membrane module 10, in the reverse osmosis membrane water purifier 100, a water faucet (not shown) downstream of the permeate water passage 30 is closed, and an on-off valve 40A in the return water passage 40 is open. In this state, permeated water discharged from the reverse osmosis membrane module 10 flows into the return water passage 40 from a branch point P1 in the permeate water passage 30. The permeated water that has flowed into the return water passage 40 flows into the inlet water passage 20 as return permeated water at a junction P2, which is the downstream end of the return water passage 40. The return permeated water that has flowed into the inlet water passage 20 from the junction P2 is merged with the raw water. This mixed water, consisting of the raw water and permeated water, is pressurized by a pump 20B and introduced back into the reverse osmosis membrane module 10.

[0035] On the other hand, during flushing of the reverse osmosis membrane module 10, the non-permeate water flow section 50 has two selector valves 61, 62 serving as the flow rate regulator 60, with the first selector valve 61 provided in the first flow path 51 closed and the second selector valve 62 provided in the second flow path 52 opened. As a result, the non-permeate water discharged from the reverse osmosis membrane module 10 flows through the second flow path 52 and is discharged.

[0036] As described above, the second flow path 52 allows the non-permeated water to flow at a flow rate lower than the flow rate of the non-permeated water flowing through the first flow path 51. Specifically, the second flow path 52 is provided with a second flow control valve 64. The second flow control valve 64 freely adjusts the flow rate of the non-permeated water flowing through the second flow path 52. By adjusting the second flow control valve 64, the flow rate of the non-permeated water flowing through the second flow path 52 can be made lower than that when flowing through the first flow path 51. The flow control unit 60 switches the flow path using the switching valves 61 and 62 so that the non-permeated water flows through the second flow path 52. By switching the flow path, the flow control unit 60 adjusts the flow rate of water flowing through the non-permeated water flow unit 50 during flushing of the reverse osmosis membrane module 10 to a flow rate lower than that during purified water production.

[0037] In this embodiment, the flow rate of the non-permeated water flowing through the second flow path 52 is set to approximately 20% of the flow rate of the mixed water introduced into the reverse osmosis membrane module 10 during flushing. Specifically, in this embodiment, approximately 20% of the mixed water introduced into the reverse osmosis membrane module 10 during flushing is discharged as wastewater, and approximately 80% is sent upstream again as return permeate to become mixed water. In other words, the reverse osmosis membrane water purifier 100 throttles the flow rate of the non-permeated water flowing through the second flow path 52 so that the proportion of return permeate in the mixed water is approximately 80%.

[0038] During flushing of the reverse osmosis membrane module 10, the pump 20B remains in the state it was in when purified water production began, as described above. In this state, the reverse osmosis membrane water purifier 100 has a faucet (not shown) downstream of the permeate water passage 30 closed. The generated permeate flows from the branch point P1 in the permeate water passage 30 into the return water passage 40 and merges with the raw water as return permeate at the junction P2, the downstream end of the return water passage 40. Because the return permeate acts as resistance, the reverse osmosis membrane water purifier 100 reduces the amount of raw water supplied to the pump 20B via the prefilter 20A during flushing compared to when purified water is produced, and also reduces the amount of water permeating the reverse osmosis membrane 10A. Furthermore, because the only water outlet is the discharge at the downstream end of the non-permeate water passage 50, the amount of water discharged as non-permeate is approximately equivalent to the amount of raw water supplied to the pump 20B via the prefilter 20A.

[0039] Therefore, in this embodiment, the flow rate adjuster 60 adjusts the flow rate of water flowing through the non-permeated water flow section 50 during flushing of the reverse osmosis membrane module 10 to a lower flow rate than when purified water is produced. Specifically, the flow rate adjuster 60 switches the flow path of the non-permeated water flow section 50 from the first flow path 51 to the second flow path 52 during flushing of the reverse osmosis membrane module 10. The second flow path 52 flows the non-permeated water at a lower flow rate than the first flow path 51. As a result, the reverse osmosis membrane water purifier 100 reduces the flow rate of non-permeated water flowing through the non-permeated water flow section 50 compared to when purified water is produced, and the amount of wastewater during flushing of the reverse osmosis membrane module 10 can be reduced compared to when purified water is produced.

[0040] During flushing of the reverse osmosis membrane module 10, the reverse osmosis membrane water purifier 100 adjusts the flow rate of non-permeated water flowing through the non-permeated water flow section 50 to a lower flow rate than during purified water production. As a result, during flushing, the reverse osmosis membrane water purifier 100 ensures the flow rate of permeated water that permeates the reverse osmosis membrane 10A and returns upstream via the return water flow section 40, and also reduces the amount of raw water that flows into the pump via the prefilter 20A. During flushing, if the proportion of return permeated water in the mixed water introduced into the reverse osmosis membrane module 10 is small, the TDS concentration in the mixed water may not be sufficiently reduced. However, by adjusting the flow rate of non-permeated water to a lower flow rate than during purified water production, the proportion of return permeated water in the mixed water can be relatively increased.

[0041] During flushing, the reverse osmosis membrane water purifier 100 throttles the flow rate of the non-permeated water discharged as wastewater, thereby ensuring the flow rate of the return permeated water and reducing the amount of raw water flowing into the pump via the prefilter 20A. This relatively increases the flow rate of the return permeated water in the mixed water, thereby lowering the TDS concentration of the mixed water compared to the raw water. As a result, during flushing, the reverse osmosis membrane water purifier 100 introduces mixed water with a reduced TDS concentration compared to the raw water into the reverse osmosis membrane module 10. By filling the reverse osmosis membrane module 10 with water with a reduced TDS concentration and shutting down operation in this state, the reverse osmosis membrane water purifier 100 reduces the total amount of dissolved solids that permeate downstream of the reverse osmosis membrane 10A due to creeping. As a result, the TDS concentration of the discharged water can be prevented from increasing when purified water production is resumed.

[0042] In the reverse osmosis membrane water purifier according to the present disclosure, the ratio of the flow rate of the return permeate to the flow rate of the mixed water can be, for example, 75% or more and 85% or less. In other words, in the reverse osmosis membrane water purifier according to the present disclosure, the ratio of the flow rate of the non-permeate discharged as wastewater to the flow rate of the mixed water introduced into the reverse osmosis membrane module during flushing can be, for example, 15% or more and 25% or less. When adjusted within this range, the amount of wastewater discharged during flushing can be sufficiently reduced, and the TDS concentration in the initial water can be sufficiently reduced.

[0043] FIG. 4 is a graph showing the relationship between the recovery rate during flushing and the peak value of the TDS concentration in the initial water, which was experimentally determined by the inventors. Note that FIG. 4 also shows the results of experiments conducted by varying the recovery rate during flushing under two conditions: a recovery rate of 70% during purified water generation and a recovery rate of 80% during purified water generation. As described above, the recovery rate during flushing refers to the ratio of the flow rate of the return permeate to the flow rate of the mixed water introduced into the reverse osmosis membrane module during flushing. For example, a recovery rate of 80% during flushing is equivalent to a flushing rejection rate of 20%. As shown in FIG. 4, the peak value of the TDS concentration in the initial water rises sharply above 125 ppm when the recovery rate exceeds 85%, i.e., when the rejection rate falls below 15%. This indicates that a recovery rate exceeding 85% during flushing actually increases the peak value of the TDS concentration.

[0044] For example, the standard of Guangdong Province, China (T / GDEACC 34-2020) stipulates that the peak TDS concentration of the initial water in a water purifier using a reverse osmosis membrane must be 125 ppm or less. In the graph of Figure 4, a TDS concentration of 125 ppm or less is met when the recovery rate is 85% or less (a waste rate of 15% or more).

[0045] On the other hand, according to the graph in Figure 4, the minimum peak value of the TDS concentration in the initial water is approximately 105 ppm, which is shown near a recovery rate of 80% (a discard rate of 20%). Furthermore, although the peak value of the TDS concentration in the initial water increases as the recovery rate decreases between 80% and 70%, no sudden change is observed. However, a decrease in recovery rate means an increase in the amount of wastewater. Therefore, the recovery rate range in which the peak value of the TDS concentration in the initial water can be effectively suppressed and the amount of wastewater can be reduced is 70% to 85% (a discard rate of 15% to 30%), preferably 73% to 83%. In other words, the discard rate range in which the peak value of the TDS concentration in the initial water can be effectively suppressed and the amount of wastewater can be reduced is 15% to 30%, preferably 17% to 27%.

[0046] As described above, the reverse osmosis membrane water purifier 100 according to the first embodiment includes the reverse osmosis membrane module 10, the inlet water flow section 20, the pump 20B, the permeate water flow section 30, the return water flow section 40, the non-permeate water flow section 50, and the flow rate adjustment section 60. The reverse osmosis membrane module 10 has a reverse osmosis membrane 10A. The inlet water flow section 20 forms a flow path through which water introduced into the reverse osmosis membrane module 10 flows. The pump 20B is provided in the inlet water flow section 20 and pressurizes the water introduced into the reverse osmosis membrane module 10. The permeate water flow section 30 forms a flow path through which permeate that has permeated through the reverse osmosis membrane 10A is discharged from the reverse osmosis membrane module 10. The return water flow section 40 forms a flow path through which the permeate discharged from the reverse osmosis membrane module 10 is returned as return permeate to the inlet water flow section 20 upstream of the pump. The non-permeate water flow section 50 forms a flow path through which non-permeate water discharged from the reverse osmosis membrane module 10 flows without passing through the reverse osmosis membrane 10A. The flow rate adjustment section 60 adjusts the flow rate of water flowing through the non-permeate water flow section 50. The inlet water flow section 20 introduces raw water supplied from a water supply source into the reverse osmosis membrane module 10 during purified water production, and introduces mixed water obtained by mixing raw water and return permeate water into the reverse osmosis membrane module 10 during flushing of the reverse osmosis membrane module 10. The flow rate adjustment section 60 adjusts the flow rate of water flowing through the non-permeate water flow section 50 during flushing of the reverse osmosis membrane module 10 to a lower flow rate than during purified water production.

[0047] With this configuration, the reverse osmosis membrane water purifier 100 can further reduce the TDS concentration of the water discharged at the beginning of purified water production and the wastewater flow rate compared to conventional systems. That is, when flushing the reverse osmosis membrane module 10, the reverse osmosis membrane water purifier 100 can return the permeated water upstream of the pump 20B through the return water passage 40 and mix it with the raw water to produce mixed water. This allows the reverse osmosis membrane water purifier 100 to introduce mixed water, which has a lower TDS concentration than the raw water, into the reverse osmosis membrane module 10 during flushing, and to discharge and replace the water with a relatively high TDS concentration that remains within the reverse osmosis membrane module 10 immediately after purified water production. As a result, the reverse osmosis membrane water purifier 100 can reduce the total amount of dissolved solids inside compared to when flushing with raw water, thereby suppressing an increase in the TDS concentration of the retained water.

[0048] The reverse osmosis membrane water purifier 100 can further reduce the wastewater flow rate compared to conventional systems. In the reverse osmosis membrane water purifier 100, the mixing ratio of raw water and return permeate during flushing of the reverse osmosis membrane module 10 is determined by adjusting the flow rate of non-permeate using the flow rate adjuster 60. In the reverse osmosis membrane water purifier 100, if the output of the pump 20B is kept constant from the time purified water is produced until the end of flushing, the flow rate of non-permeate discharged as wastewater must be reduced to achieve a desired ratio of return permeate in the mixed water. That is, the reverse osmosis membrane water purifier 100 effectively reduces the TDS concentration in the initial water by reducing the wastewater volume, thereby achieving a lower wastewater volume during flushing than the wastewater volume during purified water production.

[0049] In the reverse osmosis membrane water purifier 100, the non-permeated water flow section 50 forms a first flow path 51 and a second flow path 52 that passes non-permeated water at a flow rate lower than that of the first flow path 51. The flow rate adjustment section 60 has a first switching valve 61 and a second switching valve 62 that serve as switching valves that pass non-permeated water through the first flow path 51 during purified water production and pass non-permeated water through the second flow path 52 during flushing of the reverse osmosis membrane module 10. Therefore, the reverse osmosis membrane water purifier 100 can achieve a reduction in the wastewater flow rate during flushing with a simple configuration.

[0050] In the reverse osmosis membrane water purifier 100, the flow rate adjustment unit 60 has flow rate adjustment valves 63, 64 that adjust the flow rate of non-permeated water flowing through the non-permeated water flow unit 50. Therefore, the reverse osmosis membrane water purifier 100 can freely adjust the flow rate of non-permeated water discharged as wastewater. Of the two flow rate adjustment valves 63, 64, the first flow rate adjustment valve 63 is provided in the first flow path 51, and the second flow rate adjustment valve 64 is provided in the second flow path 52. Therefore, the reverse osmosis membrane water purifier 100 can freely adjust the wastewater flow rate both during purified water production and during flushing.

[0051] The reverse osmosis membrane water purifier 100 includes a control unit 70 that controls the flow rate adjustment unit 60 to adjust the flow rate of non-permeated water during flushing of the reverse osmosis membrane module 10. Therefore, the reverse osmosis membrane water purifier 100 can automatically adjust the flow rate of non-permeated water during flushing.

[0052] In the reverse osmosis membrane water purifier 100, the flow rate adjusting unit 60 adjusts the ratio of the flow rate of the non-permeated water to the flow rate of the mixed water (water introduced into the reverse osmosis membrane module 10) so that it is approximately 20% during flushing of the reverse osmosis membrane module 10. This allows the reverse osmosis membrane water purifier 100 to more effectively reduce the TDS concentration in the initial water.

[0053] The present disclosure is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present disclosure.

[0054] The configuration of the reverse osmosis membrane water purifier according to the present disclosure is not limited to the configuration exemplified in the above embodiment.

[0055] The configuration for adjusting the flow rate of water flowing through the non-permeate water flow section during flushing of the reverse osmosis membrane module to a lower flow rate than during purified water production is not limited to the configuration of forming two flow paths with different flow rates as in the above embodiment. As a configuration for adjusting the flow rate of water flowing through the non-permeate water flow section during flushing of the reverse osmosis membrane module to a lower flow rate than during purified water production, for example, the non-permeate water flow section may have a single flow path provided with a flow control valve that can freely adjust the flow rate. In this case, the non-permeate water flow section can use the flow control valve to adjust the flow rate of non-permeate water flowing during both purified water production and during flushing of the reverse osmosis membrane module.

[0056] In the reverse osmosis membrane water purifier according to the present disclosure, the non-permeate water flow section does not necessarily have to form two flow paths, the first flow path and the second flow path. For example, the non-permeate water flow section may form only one flow path. In this case, the flow rate adjustment section may include a flow rate adjustment valve that adjusts the flow rate of the non-permeate water flowing through the non-permeate water flow section during purified water production and during flushing of the reverse osmosis membrane module. When the non-permeate water flow section forms the first flow path and the second flow path, their downstream ends may be common, where the first flow path and the second flow path merge, or they may be separate.

[0057] In the reverse osmosis membrane water purifier according to the present disclosure, the pre-filter, post-filter, etc. are not essential components. When a pre-filter and a post-filter are provided, their configurations are not limited to those exemplified in the above embodiment.

[0058] Experiments were conducted to confirm the effectiveness of the reverse osmosis membrane water purifier according to the present disclosure. In the experiments, purified water was produced using the method described in the above embodiment, followed by flushing. The following measurements were made: (1) the change in TDS concentration depending on the discharge rate from the start of purified water discharge; and (2) the wastewater flow rate during flushing. In the experiments, measurements of (1) and (2) were also performed for Comparative Example 1 and Comparative Example 2. Comparative Example 1 is an example in which flushing is performed using only raw water, as in the conventional example, and the flow rate of non-permeated water during flushing is set to a high flow rate, as in the conventional example. Comparative Example 2 is an example in which flushing is performed using mixed water obtained by mixing return permeated water and raw water. However, Comparative Example 2 differs from the experimental example in that the flow rate of non-permeated water is not adjusted during flushing. Because the flow rate of non-permeated water is not adjusted during flushing, Comparative Example 2 has a lower ratio of the flow rate of return permeated water to the flow rate of mixed water than the experimental example. In this respect, Comparative Example 2 also differs from the experimental example.

[0059] Regarding the production of purified water, the experimental example, comparative example 1, and comparative example 2 each produce purified water at approximately the same flow rate with approximately the same pump output. Specifically, the discharge flow rate of purified water during purified water production is approximately 2.5 L / min in all cases, and the discharge flow rate is approximately 1.0 L / min in all cases, resulting in a recovery rate of approximately 70%. In the experimental example, comparative example 1, and comparative example 2, the pump output during flushing is not changed from when purified water is produced, and the output is maintained at the same level as when purified water is produced. Other conditions, such as the raw water supply pressure and the TDS concentration of the raw water, are also the same in the experimental example, comparative example 1, and comparative example 2.

[0060] The experiment was conducted using a reverse osmosis membrane water purifier 200 shown in Fig. 5. The reverse osmosis membrane water purifier 200 includes a non-permeate water passage section 250. In the reverse osmosis membrane water purifier 200 shown in Fig. 5, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description of the components having the same reference numerals will be omitted.

[0061] In the reverse osmosis membrane water purifier 200, the non-permeated water flow section 250 differs from the non-permeated water flow section 50 in the first embodiment in that it further includes an on-off valve 265 arranged in parallel with the first flow control valve 63 in the first flow path 251. In Comparative Example 1, the on-off valve 265 is opened and closed by the control unit 270 in accordance with the start and end of flushing. When opened, the on-off valve 265 allows water to flow at a higher flow rate than when flowing through the parallel-arranged first flow control valve 63. In Comparative Example 1, flushing was performed in which non-permeated water was passed through the first flow path 251 with the on-off valve 265 open and the on-off valve 40A in the return water flow section 40 closed. In Comparative Example 2, flushing was performed in which non-permeated water was passed through the first flow path 251 with the on-off valve 265 closed and the on-off valve 40A in the return water flow section 40 open.

[0062] The experimental results are shown in Figures 6 and 7, respectively. Figure 6 shows (1) the change in TDS concentration depending on the discharge volume from the start of purified water discharge. As shown in Figure 6, the peak value of the TDS concentration in the experimental example was kept sufficiently lower than that of Comparative Examples 1 and 2. Specifically, the peak value of the TDS concentration in Comparative Example 2 was approximately 120 ppm, and the peak value of the TDS concentration in Comparative Example 1 was approximately 205 ppm. In contrast, the peak value of the TDS concentration in the experimental example was approximately 90 ppm. Thus, it was confirmed that the TDS concentration of the initial water could be sufficiently reduced in the experimental example compared to each comparative example.

[0063] 7 shows the drainage flow rate during flushing (2). As shown in FIG. 7, the drainage flow rate in the experimental example was kept sufficiently lower than that in comparative examples 1 and 2. Specifically, the drainage flow rate in comparative example 2 was approximately 1 L / min, and the drainage flow rate in comparative example 1 was approximately 3.8 L / min. In contrast, the drainage flow rate in the experimental example was approximately 0.5 L / min. Thus, it was confirmed that flushing could be performed with a sufficiently reduced drainage flow rate in the experimental example compared to each comparative example.

[0064] DESCRIPTION OF SYMBOLS 10...reverse osmosis membrane module, 10A...reverse osmosis membrane, 20...inlet water passage section, 20B...pump, 30...permeate water passage section, 40...return water passage section, 50...non-permeate water passage section, 51...first flow path, 52...second flow path, 60...flow rate adjustment section, 61, 62...switching valves (61...first switching valve, 62...second switching valve), 63, 64...flow rate adjustment valves (63...first flow rate adjustment valve, 64...second flow rate adjustment valve), 70...control section, 100...reverse osmosis membrane water purifier

Claims

1. A reverse osmosis membrane water purifier that produces purified water by processing water to pass it through a reverse osmosis membrane, comprising: a reverse osmosis membrane module having a reverse osmosis membrane; an inlet water passage section that forms a flow path through which water introduced into the reverse osmosis membrane module flows; a pump provided in the inlet water passage section that pressurizes the water introduced into the reverse osmosis membrane module; a permeate water passage section that forms a flow path through which permeate water that has permeated the reverse osmosis membrane is discharged from the reverse osmosis membrane module; a return water passage section that forms a flow path through which the permeate water discharged from the reverse osmosis membrane module is returned as return permeate water to a side upstream of the pump in the inlet water passage section; a non-permeate water passage section that forms a flow path through which non-permeate water discharged from the reverse osmosis membrane module without permeating the reverse osmosis membrane flows; and a flow rate adjustment section that adjusts the flow rate of water flowing through the non-permeate water passage section, The reverse osmosis membrane water purifier, wherein the inlet water flow section introduces raw water supplied from a water supply source into the reverse osmosis membrane module during purified water production, and introduces a mixed water of the raw water and the return permeated water into the reverse osmosis membrane module during flushing of the reverse osmosis membrane module, and the flow rate adjustment section adjusts the flow rate of water flowing through the non-permeated water flow section to a lower flow rate than when purified water is produced.

2. The reverse osmosis membrane water purifier of claim 1, wherein the non-permeated water flow section forms a first flow path and a second flow path through which the non-permeated water flows at a flow rate lower than that of the first flow path, and the flow rate adjustment section has a switching valve that switches between flowing the non-permeated water through the first flow path when generating purified water and flowing the non-permeated water through the second flow path when flushing the reverse osmosis membrane module.

3. A reverse osmosis membrane water purifier as described in any one of claims 1 and 2, wherein the flow rate adjustment section has a flow rate adjustment valve that adjusts the flow rate of the non-permeated water flowing through the non-permeated water flow section.

4. A reverse osmosis membrane water purifier as described in any one of claims 1 to 3, further comprising a control unit that performs control to adjust the flow rate of the non-permeated water by the flow rate adjustment unit during flushing of the reverse osmosis membrane module.

5. A reverse osmosis membrane water purifier as described in any one of claims 1 to 4, wherein the flow rate adjustment unit adjusts the ratio of the flow rate of the non-permeated water to the flow rate of the mixed water so that it is 15% or more and 25% or less when flushing the reverse osmosis membrane module.

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