Monitoring device

Abstract

[Problem] To provide a monitoring device that can improve the detection sensitivity for particles to be monitored in treated water obtained by wastewater treatment. [Solution] A monitoring device 4 comprises a branch pipe 402 branched from a pipe 401 that guides treated water obtained by wastewater treatment, a membrane sensor 45 that is installed in a direction intersecting the flow of the treated water flowing through the branch pipe 402 and has a filtration membrane for filtering the treated water, and a pressure sensor 46 that measures the pressure difference between a first pressure of the treated water on the upstream side of the membrane sensor 45 and a second pressure of the treated water on the downstream side of the membrane sensor 45. The filtration membrane has a pore size smaller than the particles to be monitored.

Description

monitoring device

[0001] The present invention relates to a monitoring device for detecting leakage of particles to be monitored in wastewater treatment.

[0002] US Pat. Nos. 5,899,929 and 5,929,943 disclose devices for detecting the integrity of a filtration membrane.

[0003] The device disclosed in Patent Document 1 receives permeate from a filtration membrane and detects rupture of the filtration membrane based on the pressure on the supply side of the first sensor membrane, the pressure between the first and second sensor membranes, and the pressure on the permeate side of the second sensor membrane. Here, the first sensor membrane is installed parallel to the flow of the permeate from the filtration membrane. That is, the device described in Patent Document 1 employs a cross-flow filtration method.

[0004] The device disclosed in Patent Document 2 receives permeate from a filtration membrane into a first chamber and detects rupture of the filtration membrane based on the pressure measured by a pressure gauge provided on the supply side of the sensor membrane and the pressure measured by a pressure gauge provided on the permeate side of the sensor membrane. Here, the sensor membrane provided between the first and second chambers is installed parallel to the flow of permeate from the filtration membrane. In other words, the device described in Patent Document 2 employs a cross-flow filtration method.

[0005] Devices employing a cross-flow filtration method, such as those described in Patent Documents 1 and 2, to detect target particles contained in treated water obtained by wastewater treatment have a sensor membrane whose membrane surface is arranged parallel to the flow of treated water supplied to the sensor membrane, thereby suppressing particle deposition on the sensor membrane surface due to the flow. This prevents clogging of the sensor membrane, thereby reducing the frequency of sensor membrane replacement. However, because the sensor membrane does not filter all of the target particles contained in the treated water supplied to the sensor membrane, only a portion of the target particles contained in the treated water supplied to the sensor membrane can be captured. Therefore, devices employing a cross-flow filtration method have room for improvement in terms of the difficulty of improving the sensitivity of detecting target particles contained in treated water obtained by wastewater treatment.

[0006] In contrast, a dead-end filtration system has a sensor membrane whose membrane surface is positioned across the flow of treated water supplied to the sensor membrane, and filters the entire amount of treated water supplied to the sensor membrane. This allows the entire amount of target particles contained in the treated water supplied to the sensor membrane to be captured, offering the advantage of improved sensitivity in detecting target particles contained in the treated water obtained by wastewater treatment. However, compared to a cross-flow filtration system, the dead-end filtration system also captures a greater number of particles other than the target particles. Therefore, compared to a cross-flow filtration system, a dead-end filtration system leaves room for improvement in terms of the more frequent replacement of the sensor membrane that captures the target particles and the risk of false detection of leakage of the target particles.

[0007] U.S. Patent No. 8,135,547 U.S. Patent No. 10,159,941

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a monitoring device that can improve the sensitivity in detecting particles to be monitored that are contained in treated water obtained by wastewater treatment.

[0009] A first aspect of the present invention is a monitoring device for detecting leakage of particles to be monitored during wastewater treatment, comprising: a branch pipe branching off from a pipe that conducts treated water obtained by the wastewater treatment; a membrane sensor having a filtration membrane that is installed in a direction intersecting the flow of the treated water flowing through the branch pipe and filters the treated water; and a pressure sensor that measures the differential pressure between a first pressure of the treated water upstream of the membrane sensor and a second pressure of the treated water downstream of the membrane sensor, wherein the filtration membrane has a pore size smaller than the particles to be monitored.

[0010] According to a first aspect of the present invention, a filtration membrane that filters the treated water flowing through a branch pipe is installed in a direction that crosses the flow of the treated water. In other words, the monitoring device employs a dead-end filtration method. Furthermore, the filtration membrane has a pore size that is smaller than the target particles, so that the target particles can be more reliably captured. Therefore, the monitoring device can improve the sensitivity in detecting the target particles.

[0011] A second aspect of the present invention is the monitoring device according to the first aspect of the present invention, characterized in that the filtration membrane is a track-etched membrane.

[0012] According to the second aspect of the present invention, since the filtration membrane is a track-etched membrane, the pores formed in the filtration membrane have a uniform pore size distribution, which allows the monitoring device to reduce false positives regarding leakage of the monitored particles and improve the sensitivity of the detection of the monitored particles.

[0013] A third aspect of the present invention is a monitoring device according to the first or second aspect of the present invention, characterized in that the pore size is formed to allow proteins smaller than the particles to be monitored to pass through.

[0014] According to the third aspect of the present invention, the filtration membrane allows proteins smaller than the particles to be monitored to pass through. That is, fewer particles are captured by the filtration membrane per unit time. Therefore, the monitoring device can extend the time until the filtration membrane needs to be replaced, thereby improving the sensitivity in detecting the particles to be monitored while reducing the frequency of replacement of the filtration membrane.

[0015] A fourth aspect of the present invention is a monitoring device according to any one of the first to third aspects of the present invention, characterized in that the protein adsorption rate of the filtration membrane is lower than the protein adsorption rates of cellulose acetate (CA), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0016] According to the fourth aspect of the present invention, the protein adsorption rate of the filtration membrane is smaller than a predetermined value. This makes it possible to further prevent proteins from adsorbing to the filtration membrane and clogging the filtration membrane. This allows the monitoring device to further improve the sensitivity in detecting particles to be monitored while reducing the frequency of replacing the filtration membrane.

[0017] A fifth aspect of the present invention is a monitoring device according to any one of the first to fourth aspects of the present invention, characterized in that the pressure sensor calculates a filtration resistance by dividing the differential pressure by a filtration flux, and detects the leakage based on the ratio between the time average value of the filtration resistance at a first timing and the time average value of the filtration resistance at a second timing that is later than the first timing.

[0018] According to the fifth aspect of the present invention, the monitoring device can detect leakage of monitored particles with higher accuracy regardless of temporal fluctuations in the flow rate of the treated water flowing through the branch pipe.

[0019] A sixth aspect of the present invention is a monitoring device according to any one of the first to fourth aspects of the present invention, characterized in that the pressure sensor calculates a filtration resistance based only on the differential pressure, and detects the leak based on the filtration resistance.

[0020] According to the sixth aspect of the present invention, the monitoring device can detect leakage of particles to be monitored with higher accuracy.

[0021] A seventh aspect of the present invention is a monitoring device characterized in that, in any one of the first to sixth aspects of the present invention, it further comprises an air vent valve that is provided upstream of the membrane sensor and vents air that has become mixed into the treated water flowing through the branch pipe toward the membrane sensor.

[0022] According to the seventh aspect of the present invention, the monitoring device can remove air mixed in the treated water and reduce the variation in the value of the monitoring index (e.g., filtration resistance), thereby enabling the monitoring device to detect the particles to be monitored with higher accuracy and detect leakage of the particles to be monitored with higher accuracy.

[0023] An eighth aspect of the present invention is a monitoring device according to any one of the first to seventh aspects of the present invention, further comprising a concentration equalization means provided upstream of the membrane sensor for equalizing the concentration of the treated water.

[0024] According to the eighth aspect of the present invention, the concentration equalizing means can equalize the concentration of the entire treated water obtained by wastewater treatment. This allows the monitoring device to reduce the concentration polarization of solids throughout the entire treated water obtained by wastewater treatment. Therefore, even if the flow rate of the treated water flowing through the branch pipe is relatively small compared to the total flow rate of the treated water obtained by wastewater treatment, it is possible to detect leakage of the monitored particles with higher accuracy.

[0025] According to the present invention, it is possible to provide a monitoring device that can improve the sensitivity in detecting particles to be monitored that are contained in treated water obtained by wastewater treatment.

[0026] It is a block diagram showing a monitoring device according to an embodiment of the present invention. It is a schematic cross-sectional view showing a filtration membrane of a membrane sensor of the present embodiment. It is a schematic cross-sectional view showing a filtration membrane of a membrane sensor of a comparative example. It is a graph illustrating an example of the results of a study carried out by the present inventor.

[0027] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below are preferred specific examples of the present invention, and therefore various technically preferable limitations are applied, but the scope of the present invention is not limited to these aspects unless otherwise specified in the following description to the effect that the present invention is limited. Furthermore, in each drawing, similar components are given the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0028] FIG. 1 is a block diagram showing a monitoring device according to an embodiment of the present invention. The monitoring device 4 according to this embodiment detects leakage of monitored particles during wastewater treatment. For example, the wastewater treatment may include biological treatment and membrane treatment. However, the wastewater treatment according to this embodiment does not necessarily include biological treatment and membrane treatment, and may include all clarification processes using, for example, sand filtration, fiber filtration, and thread filters. In the description of this embodiment, a case in which the wastewater treatment includes biological treatment and membrane treatment will be described as an example. In this case, as shown in FIG. 1 , the monitoring device 4 according to this embodiment detects leakage of monitored particles due to damage to the membrane used in membrane treatment 3 in wastewater treatment that involves biological treatment 2 and membrane treatment 3.

[0029] The biological treatment 2 step shown in Figure 1 is a step of introducing water to be treated into a biological reactor where biological treatment is performed to obtain biologically treated water. Biological treatment 2 is not particularly limited as long as it treats the water to be treated introduced into the biological reactor in the presence of microorganisms. In other words, biological treatment 2 may be aerobic biological treatment or anaerobic biological treatment. In other words, the microorganisms may be aerobic microorganisms or anaerobic microorganisms. Examples of biological treatment 2 include an activated sludge method (including a membrane separation activated sludge method), a carrier method, and a fixed-bed biofilm method.

[0030] By the biological treatment 2 step, biologically treated water in which the organic water pollutants contained in the water to be treated have been reduced is obtained.

[0031] The membrane treatment 3 shown in FIG. 1 may be performed after the biological treatment 2, or may be performed at the same stage as the biological treatment 2. Specifically, the membrane separation device (not shown) used in the membrane treatment 3 may be provided outside the biological reaction tank used in the biological treatment 2, or may be provided inside the biological reaction tank. When the membrane separation device is provided outside the biological reaction tank, the membrane separation device performs solid-liquid separation on the biologically treated water obtained by the step of the biological treatment 2 to obtain membrane-treated water. On the other hand, when the membrane separation device is provided inside the biological reaction tank, the membrane separation device performs solid-liquid separation on the liquid in the biological reaction tank to obtain membrane-treated water. The membrane-treated water of this embodiment is an example of the "treated water" of the present invention.

[0032] The membrane used in membrane treatment 3, i.e., the membrane provided in the membrane separation device, is not particularly limited as long as it can perform solid-liquid separation of the biological treatment water and the liquid in the biological reactor. Examples of the membrane used in membrane treatment 3 include microfiltration membranes (MF membranes) and ultrafiltration membranes (UF membranes). Examples of the shape of the membrane used in membrane treatment 3 include hollow fiber membranes, tubular membranes, and flat membranes. Examples of the material of the membrane used in membrane treatment 3 include organic membranes such as cellulose acetate, polyvinylidene fluoride, polyolefin, chlorinated polyethylene, polyamide, polyacrylonitrile, and polytetrafluoroethylene, and inorganic membranes such as ceramics (e.g., mullite, alumina, and zirconia).

[0033] As mentioned above, the wastewater treatment of this embodiment does not necessarily have to include membrane treatment. For example, the biologically treated water may be obtained by solid-liquid separation using solid-liquid separation means other than a membrane separator (e.g., a settling tank). In this case, the biologically treated water of this embodiment is an example of the "treated water" of the present invention.

[0034] The monitoring device 4 shown in FIG. 1 includes a pipe 401 , a branch pipe 402 , a water supply switching valve 42 , a membrane sensor 45 , a differential pressure sensor 46 , and a flow rate sensor 47 .

[0035] Pipe 401 guides the membrane-treated water obtained by membrane treatment 3. Branch pipe 402 branches off from pipe 401 and guides at least a portion of the membrane-treated water flowing through pipe 401 toward membrane sensor 45. Water supply switching valve 42 is provided in branch pipe 402 and switches between a state in which at least a portion of the membrane-treated water flowing through pipe 401 flows toward membrane sensor 45 and a state in which the membrane-treated water flowing through pipe 401 is prevented from flowing toward membrane sensor 45. In other words, when water supply switching valve 42 is open, at least a portion of the membrane-treated water flowing through pipe 401 flows toward membrane sensor 45. On the other hand, when water supply switching valve 42 is closed, the membrane-treated water flowing through pipe 401 does not flow toward membrane sensor 45 but is instead guided to a downstream process of monitoring device 4.

[0036] The membrane sensor 45 has a filtration membrane, and filters the membrane-treated water flowing through the branch pipe 402. The filtration membrane of the membrane sensor 45 is installed in a direction intersecting the flow of the membrane-treated water, and filters the entire amount of the membrane-treated water flowing through the branch pipe 402 to capture particles to be monitored. In other words, the membrane sensor 45 employs a dead-end filtration method. The filtration membrane of the membrane sensor 45 has a pore size smaller than the particles to be monitored.

[0037] Here, in this specification, the term "dead-end filtration method" refers to a method in which a filtration membrane that filters treated water such as membrane-treated water or biologically treated water is installed in a direction that intersects (specifically, perpendicular to) the flow of treated water flowing through the branch pipe 402, and filters the entire amount of treated water flowing through the branch pipe 402. On the other hand, in this specification, the term "cross-flow filtration method" refers to a method in which a filtration membrane that filters treated water such as membrane-treated water or biologically treated water is installed in a direction that is parallel to the flow of treated water flowing through the branch pipe 402, and filters a portion of the treated water flowing through the branch pipe 402.

[0038] The monitored particles captured by the filtration membrane of the membrane sensor 45 are particles that are not contained in the membrane-treated water when the membrane used in membrane process 3 is not damaged, and are particles with a diameter of, for example, approximately 3 μm or more. Examples of monitored particles captured by the filtration membrane of the membrane sensor 45 include Cryptosporidium and Giardia. On the other hand, particles other than the monitored particles captured by the filtration membrane of the membrane sensor 45 are particles that are contained in the membrane-treated water even when the membrane used in membrane process 3 is not damaged, and are particles with a diameter of, for example, less than approximately 1 μm. Examples of particles other than the monitored particles captured by the filtration membrane of the membrane sensor 45 include proteins. Details of the filtration membrane of the membrane sensor 45 will be described later.

[0039] The differential pressure sensor 46 measures the differential pressure between a first pressure of the membrane-treated water at a first position A1 on the upstream side (i.e., the primary side) of the membrane sensor 45 and a second pressure of the membrane-treated water at a second position A2 on the downstream side (i.e., the secondary side) of the membrane sensor 45. The differential pressure sensor 46 of this embodiment is an example of the "pressure sensor" of the present invention. The first position A1 is an arbitrary position on the branch pipe 402 on the upstream side of the membrane sensor 45. The second position A2 is an arbitrary position on the branch pipe 402 on the downstream side of the membrane sensor 45.

[0040] The differential pressure sensor 46 calculates the filtration resistance as a monitoring index and detects leakage of particles to be monitored based on the filtration resistance. For example, the differential pressure sensor 46 calculates the filtration resistance by dividing the differential pressure between the first pressure and the second pressure by the filtration flux. In this specification, the term "filtration flux" refers to the amount of water filtered through the membrane per unit membrane area and unit time (m ３ / (m ２ d) or m / d), for example, the membrane area (1 m ２ Daily membrane filtered water volume per unit (m ３ / d). The differential pressure sensor 46 detects leakage of the monitored particles based on the ratio between the time average value of the filtration resistance at the first timing and the time average value of the filtration resistance at a second timing that is later than the first timing. For example, the second timing is a time that is at least one hour and not more than six hours after the first timing. Alternatively, when the flow rate of the membrane-treated water flowing through the branch pipe 402 is stable, the differential pressure sensor 46 may calculate the filtration resistance based only on the differential pressure between the first pressure and the second pressure, and detect leakage of the monitored particles based on the filtration resistance.

[0041] The filtration flux in the membrane sensor 45 of this embodiment is, for example, about 5 m / d, which is higher than the filtration flux in a typical membrane separation activated sludge process (generally 1 m / d or less).

[0042] Note that a first pressure sensor that measures the first pressure of the membrane-treated water at the first position A1 and a second pressure sensor that measures the second pressure of the membrane-treated water at the second position A2 may be provided instead of the differential pressure sensor 46. In this case, a control unit (not shown) calculates the differential pressure between the first pressure and the second pressure based on a detection signal related to the first pressure received from the first pressure sensor and a detection signal related to the second pressure received from the second pressure sensor.

[0043] 1 , the flow rate sensor 47 measures the flow rate of the membrane-treated water flowing through the branch pipe 402 downstream (i.e., the secondary side) of the membrane sensor 45. However, since the monitoring device 4 according to this embodiment employs a dead-end filtration type membrane sensor 45, the flow rate of the membrane-treated water flowing through the branch pipe 402 is substantially the same everywhere. Therefore, the location of the flow rate sensor 47 is not limited to the downstream side of the membrane sensor 45, and it may also be upstream of the membrane sensor 45.

[0044] As shown in FIG. 1 , the monitoring device 4 may further include a concentration equalizing means 41 , a water supply rate adjusting valve 43 , a water supply pump 44 , and an air vent valve 48 .

[0045] The concentration equalizing means 41 is provided upstream of the membrane sensor 45. Specifically, the concentration equalizing means 41 is provided on the pipe 401 upstream of the part where the branch pipe 402 is connected to the pipe 401 (i.e., the branch section). The concentration equalizing means 41 can equalize the concentration of the membrane-treated water. Examples of the concentration equalizing means 41 include a line mixer and an agitator.

[0046] 1, the water supply rate adjusting valve 43 is provided in the branch pipe 402 between the water supply switching valve 42 and the water supply pump 44, and adjusts the flow rate of the membrane-treated water flowing through the branch pipe 402. However, the water supply rate adjusting valve 43 may be provided on the discharge side of the water supply pump 44 as long as it can adjust the flow rate of the membrane-treated water flowing through the branch pipe 402. Alternatively, the water supply rate adjusting valve 43 may be omitted and the flow rate of the membrane-treated water flowing through the branch pipe 402 may be adjusted by the water supply switching valve 42. Furthermore, the water supply rate adjusting valve 43 can be omitted when a variable-flow constant flow pump is used as the water supply pump 44 or when a flow rate varying means such as an inverter is provided in the water supply pump 44.

[0047] As shown in Figure 1, the water supply pump 44 is provided in the branch pipe 402 between the water supply rate adjustment valve 43 and the membrane sensor 45, and sucks membrane-treated water from the pipe 401 toward the branch pipe 402 and sends the sucked membrane-treated water toward the membrane sensor 45.

[0048] 1 , the air vent valve 48 is provided in the air discharge pipe 403, and can discharge air mixed in the membrane-treated water flowing through the branch pipe 402 toward the membrane sensor 45 through the air discharge pipe 403. The air discharge pipe 403 is connected to the branch pipe 402 on the upstream side of the membrane sensor 45. By opening the air vent valve 48, the air mixed in the membrane-treated water can be discharged through the air discharge pipe 403.

[0049] Air mixed in the membrane-treated water flowing through the branch pipe 402 toward the membrane sensor 45 is lighter than the liquid membrane-treated water, and therefore tends to accumulate at the top of the branch pipe 402 in the vertical direction. Therefore, the air vent valve 48 is preferably installed at the topmost vertical position of the branch pipe 402. In the case of the dead-end filtration method shown in FIG. 1 , the piping leading the membrane-treated water to the membrane sensor (branch pipe 402 in FIG. 1 ) tends to be longer than the cross-flow filtration method described in Patent Documents 1 and 2. This makes it more likely for air to accumulate inside the piping leading the membrane-treated water to the membrane sensor. Air accumulation inside the piping leading the membrane-treated water to the membrane sensor is likely to cause measurement errors in the differential pressure sensor. In this embodiment, as shown in FIG. 1 , the air vent valve 48 can eliminate air accumulation in the branch pipe 402, thereby improving the measurement accuracy of the differential pressure sensor 46. This improves the detection accuracy of the membrane sensor 45.

[0050] As described above, the membrane sensor 45 of this embodiment employs a dead-end filtration method. Therefore, the filtration membrane of the membrane sensor 45 can capture more target particles than a membrane sensor employing a cross-flow filtration method. This allows the monitoring device 4 of this embodiment to improve its sensitivity in detecting target particles. However, because the sensor membrane employing the dead-end filtration method filters the entire amount of treated water, it also captures more particles other than the target particles than a membrane sensor employing a cross-flow filtration method. Therefore, a membrane sensor employing a dead-end filtration method may require more frequent replacement of the filtration membrane that captures target particles, or may be more susceptible to false detection of leakage of target particles than a membrane sensor employing a cross-flow filtration method.

[0051] In contrast, in the monitoring device 4 according to this embodiment, the filtration membrane of the membrane sensor 45 has a pore size smaller than the particles to be monitored. Furthermore, the pore size distribution of the pores formed in the filtration membrane of the membrane sensor 45 is narrower than a predetermined distribution. Because the dead-end filtration method is adopted and the pore size of the filtration membrane of the membrane sensor 45 is more uniform, the filtration membrane of the membrane sensor 45 allows particles other than the particles to pass through (e.g., proteins smaller than the particles to be monitored), while more reliably capturing the particles to be monitored (e.g., Cryptosporidium, Giardia, etc.). Therefore, the monitoring device 4 according to this embodiment can reduce false detections of leakage of the particles to be monitored and improve the sensitivity in detecting the particles to be monitored. Furthermore, the protein adsorption rate of the filtration membrane of the membrane sensor 45 is smaller than a predetermined value. Therefore, it is possible to prevent proteins contained in the treated water as particles other than the particles to be monitored from being adsorbed onto the filtration membrane of the membrane sensor 45. As a result, the monitoring device 4 according to this embodiment can reduce the frequency of replacing the filtration membrane of the membrane sensor 45.

[0052] The membrane sensor 45 of this embodiment will be further described below with reference to the drawings. Fig. 2 is a schematic cross-sectional view showing the filtration membrane of the membrane sensor of this embodiment. Fig. 3 is a schematic cross-sectional view showing the filtration membrane of a membrane sensor of a comparative example. Figs. 2(a) and 3(a) show the state before the particles 52 to be monitored are trapped by the filtration membrane. Figs. 2(b) and 3(b) show the state after the particles 52 to be monitored are trapped by the filtration membrane.

[0053] The particle size of the protein mentioned above as an example of particles 51 other than the target of monitoring is smaller than the target particle 52. Proteins are known to adsorb to the surfaces of materials such as plastic, glass, and metal when dissolved in water. When the water to be treated is organic wastewater, the protein concentration is higher not only in the water to be treated but also in treated water such as biologically treated water and membrane treated water, compared to when the water to be treated is inorganic wastewater.

[0054] First, the filtration membrane 451A of the membrane sensor 45A of the comparative example will be described with reference to Figures 3(a) and 3(b). The pore size distribution of the pores formed in the filtration membrane 451A is relatively wide. In other words, the diameters of the pores formed in the filtration membrane 451A are relatively non-uniform. Examples of materials for the filtration membrane 451A of the comparative example include cellulose acetate (CA), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0055] When the pore size distribution is relatively wide, i.e., when the pore size is relatively non-uniform, as in the filtration membrane 451A of the comparative example, many particles 51 other than the target particles to be monitored, such as proteins, are captured by the filtration membrane 451A. That is, as shown in FIG. 3A, even if the membrane used in the membrane process 3 is not damaged, many particles 51 other than the target particles to be monitored are captured by the filtration membrane 451A. Therefore, even if the membrane used in the membrane process 3 is not damaged, the differential pressure between the first pressure and the second pressure described above with reference to FIG. 1 may become the same as the differential pressure when the membrane used in the membrane process 3 is damaged. In this case, even if the membrane used in the membrane process 3 is not damaged, the differential pressure sensor 46 may erroneously detect that the membrane used in the membrane process 3 is damaged. 3B, when the membrane used in the membrane treatment 3 is damaged and the particles 52 to be monitored are trapped by the filtration membrane 451A, the pressure difference between the first pressure and the second pressure, in other words, the filtration resistance as a monitoring index, may not easily show an inflection point. Furthermore, since the filtration membrane 451A may be clogged with particles 51 other than the particles to be monitored, the filtration membrane 451A may need to be replaced more frequently.

[0056] In contrast, as shown in FIGS. 2A and 2B, the filtration membrane 451 of the membrane sensor 45 of this embodiment has pores 452 with a pore size smaller than the particle 51 to be monitored. The pore size distribution of the pores 452 formed in the filtration membrane 451 is narrower than a predetermined distribution. In other words, the diameters of the pores 452 formed in the filtration membrane 451 are relatively uniform. The pore size distribution of the pores 452 formed in the filtration membrane 451 is narrower than the pore size distributions of cellulose acetate (CA), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). Examples of the filtration membrane 451 of this embodiment include track-etched membranes made of materials such as polycarbonate (PC) and polyesters (PEs). Herein, the term "track-etched membrane" refers to a filtration membrane manufactured using an etching process using an ion beam. The track-etched membrane has characteristics such as a narrower pore size distribution and a thinner membrane thickness than polytetrafluoroethylene (PTFE) etc. Specifically, an example of the material of the filtration membrane 451 is Isopore (registered trademark) manufactured by Merck.

[0057] Furthermore, it is desirable that the pore size of the filtration membrane 451 of the membrane sensor 45 of this embodiment is large enough to capture particles to be monitored, such as cryptosporidium and giardia, and large enough to allow particles not to be monitored, such as proteins, to pass through.

[0058] Due to these technical features of the filtration membrane 451 of this embodiment, as shown in Fig. 2(a), the filtration membrane 451 of this embodiment can allow many particles 51 other than the monitoring target, such as proteins, whose particle size is smaller than the monitoring target particles 52, to pass through the holes 452. Furthermore, as shown in Fig. 2(b), the filtration membrane 451 can more reliably capture the monitoring target particles 52. Therefore, the monitoring device 4 according to this embodiment can suppress false detection of leakage of the monitoring target particles 52 and improve the sensitivity in detecting the monitoring target particles 52.

[0059] The protein adsorption rate of the filtration membrane 451 is smaller than a predetermined value. The protein adsorption rate of the filtration membrane 451 is smaller than the protein adsorption rates of cellulose acetate (CA), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). The protein adsorption rate of Isopore manufactured by Merck is 3 μg / cm ２ and the protein adsorption rate (4 μg / cm) of Omnipore (registered trademark) made by Merck, a hydrophilic polytetrafluoroethylene (PTFE) ２ ) is smaller than

[0060] This makes it possible to prevent proteins contained in treated water, such as biological treatment water or membrane-treated water, as particles 51 other than those to be monitored from being adsorbed onto the filtration membrane 451. This makes it possible to further prevent proteins from being adsorbed onto the filtration membrane 451 and clogging the filtration membrane 451. This makes it possible for the monitoring device 4 according to this embodiment to reduce the frequency with which the filtration membrane 451 provided in the membrane sensor 45 needs to be replaced.

[0061] 1 , the differential pressure sensor 46 calculates the filtration resistance by dividing the differential pressure between the first pressure and the second pressure by the filtration flux, and detects leakage of the monitored particles 52 based on the ratio between the time average value of the filtration resistance at the first timing and the time average value of the filtration resistance at the second timing after the first timing. This allows the monitoring device 4 according to this embodiment to detect leakage of the monitored particles 52 with higher accuracy, regardless of temporal fluctuations in the flow rate of the membrane-treated water flowing through the branch pipe 402.

[0062] 1, when the flow rate of the membrane-treated water flowing through the branch pipe 402 is stable, the differential pressure sensor 46 may calculate the filtration resistance based only on the differential pressure between the first pressure and the second pressure, and detect leakage of the monitored particles 52 based on the filtration resistance. Even in this case, the monitoring device 4 according to this embodiment can detect leakage of the monitored particles 52 with higher accuracy.

[0063] Furthermore, by opening the air vent valve 48 intermittently, air that has become mixed in the membrane-treated water flowing through the branch pipe 402 toward the membrane sensor 45 can be removed through the air exhaust pipe 403. For example, the air vent valve 48 opens for approximately one minute about once a day. This allows the monitoring device 4 according to this embodiment to remove air that has become mixed in the membrane-treated water and reduce variation in the value of the filtration resistance, which is a monitoring index. This allows the monitoring device 4 to detect the particles 52 to be monitored with higher accuracy and detect leakage of the particles 52 to be monitored with higher accuracy.

[0064] Furthermore, the concentration equalizing means 41 is provided upstream of the membrane sensor 45, and can equalize the concentration of the membrane-treated water. As a result, the monitoring device 4 according to this embodiment can reduce the concentration polarization of solids throughout the membrane-treated water. Therefore, even if the flow rate of the membrane-treated water flowing through the branch pipe 402 is relatively small compared to the total flow rate of the membrane-treated water flowing through the pipe 401, leakage of the monitored particles 52 can be detected with higher accuracy.

[0065] Next, an example of the results of an experiment conducted by the present inventor will be described with reference to the drawings. Fig. 4 is a graph illustrating an example of the results of a study conducted by the present inventor. The horizontal axis of the graph shown in Fig. 4 represents filtration time (min). The vertical axis of the graph shown in Fig. 4 represents filtration resistance (kPa / (m / d)).

[0066] The inventors compared the tendency of change in filtration resistance during water flow using Merck's Isopore (material: PC) and Merck's Omnipore (material: PTFE). Merck's Isopore (material: PC) is a track-etched membrane. For ease of explanation, Merck's Isopore (material: PC) will be referred to as the "first material 455" and Merck's Omnipore (material: PTFE) will be referred to as the "second material 456."

[0067] The nominal pore size of the first material 455 is 1.2 μm, which is approximately the same as the nominal pore size (1.0 μm) of the second material 456. The protein adsorption rate of the first material 455 is lower than, but approximately the same as, the protein adsorption rate of the second material 456. On the other hand, the pore size distribution of the first material 455 is narrower than that of the second material 456.

[0068] The experimental conditions were as follows: the diameter of the filtration membrane was 47 mm. The liquid to be filtered was tap water. The inventors added sludge to the tap water 60 to 90 minutes after the start of filtration. The sludge had an MLSS of 10,790 mg / L. The sludge addition rate was 100 ppm. Before the addition of sludge, the turbidity of the liquid to be filtered passed through the filtration membrane of the first material 455 was 0.12 NTU. After the addition of sludge, the turbidity of the liquid to be filtered passed through the filtration membrane of the first material 455 was 0.44 NTU. Before the addition of sludge, the turbidity of the liquid to be filtered passed through the filtration membrane of the second material 456 was 0.10 NTU. After the addition of sludge, the turbidity of the liquid to be filtered passed through the filtration membrane of the second material 456 was 0.48 NTU.

[0069] The temperature of the liquid to be filtered passing through the filtration membrane of the first material 455 is 21.2°C. The temperature of the liquid to be filtered passing through the filtration membrane of the second material 456 is 22.5°C. The filtration flux is 40 m / d. The inventor used a portable turbidity meter 2100P manufactured by HACH as the turbidity meter. The inventor also used a pressure sensor instead of a differential pressure sensor.

[0070] The inventors also calculated the filtration resistance R using the following formula: R (kPa / (m / d)) = ((Pf1 - Pf2) - (Ps1 - Ps2)) / F R: filtration resistance Pf1: primary filtration pressure during filtration [kPa] Pf2: secondary filtration pressure during filtration [kPa] Ps1: primary filtration pressure when filtration is stopped [kPa] Ps2: secondary filtration pressure when filtration is stopped [kPa] F: filtration flux [m / d] Primary filtration side: side of water to be filtered, i.e., upstream side of the filtration membrane Secondary filtration side: side of water filtered through the membrane, i.e., downstream side of the filtration membrane

[0071] An experiment was conducted under the above conditions, and an example of the change in filtration resistance over time during water flow is shown in FIG. 4 . That is, when no sludge was mixed in (before the spike shown in FIG. 4 ), it was confirmed that the increase in filtration resistance of the first material 455 was smaller than the increase in filtration resistance of the second material 456. Furthermore, it was confirmed that the presence or absence of an inflection point in filtration resistance due to the addition of sludge (spike) was easier to determine for the first material 455 than for the second material 456. That is, the rate of change in filtration resistance of the first material 455 due to the addition of sludge was greater than the rate of change in filtration resistance of the second material 456 due to the addition of sludge.

[0072] According to the graph shown in Figure 4, the nominal pore size and protein adsorption rate of the first material 455 are approximately the same as the nominal pore size and protein adsorption rate of the second material 456, and therefore the difference in the change in filtration resistance over time shown in Figure 4 is thought to be due to the wide or narrow pore size distribution.

[0073] The second material 456, which has a relatively wide pore size distribution, easily captures substances with smaller nominal pore sizes. Therefore, the filtration resistance increases even when sludge is not mixed in. As particle capture, i.e., clogging of the filtration membrane, progresses, even particles smaller than sludge (large particles) begin to accumulate on the membrane surface. Therefore, it is believed that even when sludge is mixed in, no clear inflection point occurs in the filtration resistance of the second material 456.

[0074] On the other hand, in the first material 455, which has a relatively narrow pore size distribution, the capture rate of particles smaller than the pore size is lower than the capture rate in the second material 456. Therefore, the progress of clogging of the filtration membrane is slower compared to the second material 456. With regard to the intrusion of sludge (large particles) and their deposition on the membrane surface, the clogging mechanism of the filtration membrane of the first material 455 is different from the clogging mechanism of the filtration membrane of the second material 456. Therefore, it is thought that a clear inflection point occurred in the filtration resistance of the first material 455.

[0075] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims. The configurations of the above embodiments can be partially omitted or arbitrarily combined in a different manner from the above.

[0076] 2: Biological treatment, 3: Membrane treatment, 4: Monitoring device, 41: Concentration equalization means, 42: Water supply switching valve, 43: Water supply rate adjustment valve, 44: Water supply pump, 45: Membrane sensor, 45A: Membrane sensor, 46: Differential pressure sensor, 47: Flow rate sensor, 48: Air vent valve, 51: Particles, 52: Particles, 401: Piping, 402: Branch pipe, 403: Air exhaust pipe, 451: Filtration membrane, 451A: Filtration membrane, 452: Hole, 455: First material, 456: Second material, A1: First position, A2: Second position, R: Filtration resistance

Claims

1. A monitoring device for detecting leakage of monitored particles in wastewater treatment, a branch pipe branching from the pipe for guiding treated water obtained by the wastewater treatment; a membrane sensor installed in a direction intersecting the flow of the treated water flowing through the branch pipe and having a filtration membrane for filtering the treated water; a pressure sensor that measures a differential pressure between a first pressure of the treated water upstream of the membrane sensor and a second pressure of the treated water downstream of the membrane sensor; Equipped with The monitoring device is characterized in that the filtration membrane has a pore size smaller than that of the particles to be monitored.

2. 2. The monitoring device of claim 1, wherein the filtration membrane is a track-etched membrane.

3. 2. The monitoring device according to claim 1, wherein the pore size is formed to allow proteins smaller than the particles to be monitored to pass through.

4. 2. The monitoring device of claim 1, wherein the protein adsorption rate of the filtration membrane is less than the protein adsorption rates of cellulose acetate (CA), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

5. The monitoring device described in claim 1, characterized in that the pressure sensor calculates the filtration resistance by dividing the differential pressure by the filtration flux, and detects the leakage based on the ratio between the time average value of the filtration resistance at a first timing and the time average value of the filtration resistance at a second timing after the first timing.

6. 2. The monitoring device according to claim 1, wherein the pressure sensor calculates a filtering resistance based only on the differential pressure, and detects the leakage based on the filtering resistance.

7. The monitoring device according to claim 1, further comprising an air vent valve provided upstream of the membrane sensor for venting air mixed in the treated water flowing through the branch pipe toward the membrane sensor.

8. 2. The monitoring device according to claim 1, further comprising concentration equalization means provided on the upstream side of the membrane sensor for equalizing the concentration of the treated water.