Water treatment equipment

Abstract

To provide a transmembrane pressure difference prediction method and a water treatment apparatus capable of predicting a future increase in a transmembrane pressure difference of a hollow fiber membrane module.SOLUTION: A transmembrane pressure difference prediction method for predicting a transmembrane pressure difference in a water treatment apparatus that filters raw water by use of a hollow fiber membrane module, includes: measuring, at intervals of 3 seconds or less, a pressure on at least one side of a primary side and a secondary side in each of a plurality of times of a backwash step when the backwash step of pushing treated water on the secondary side of the hollow fiber membrane module to the primary side of the hollow fiber membrane module by a pressurized medium is performed a plurality of times; predicting a future increase in a transmembrane pressure difference in the hollow fiber membrane on the basis of a difference among the plurality of times of the backwash step as a measurement result of the pressure on the at least one side; and reporting a result of the prediction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an inter-membrane differential pressure prediction method and a water treatment apparatus.

Background Art

[0002] Conventionally, a water treatment apparatus that filters raw water using a hollow fiber membrane module has been known. In this water treatment apparatus, raw water is supplied to the inside of the hollow fiber membrane module, and the raw water is permeated through the hollow fiber membrane, whereby treated water from which impurities have been removed is discharged to the outside of the hollow fiber membrane module. When filtration is performed for a certain period of time, impurities adhere to the hollow fiber membrane. As a result, the permeation resistance of the hollow fiber membrane increases, and the differential pressure between the primary side (inside) and the secondary side (outside) of the hollow fiber membrane module, which is the inter-membrane differential pressure, increases. Therefore, in this water treatment apparatus, generally, the inter-membrane differential pressure is measured in units of minutes (for example, 10 minutes) during the filtration process, and the inter-membrane differential pressure is used as a performance index of the hollow fiber membrane module.

[0003] For example, Patent Document 1 describes that at the start of the filtration process, the pressures at the primary side inlet, secondary side outlet, and primary side outlet of a separation membrane module having a hollow fiber membrane are measured, and based on this measurement result, the membrane filtration differential pressure (corresponding to the inter-membrane differential pressure), which is the difference between the pressure on the primary side and the pressure on the secondary side of the separation membrane module, is calculated. And it is described that based on the calculation result such as the membrane filtration differential pressure, the clogged portion of the separation membrane module is specified.

[0004] Also, when an increase in the inter-membrane differential pressure during the filtration process is detected, it is known to clean the hollow fiber membrane module on the assumption that the amount of impurities adhering to the hollow fiber membrane has increased and the permeation resistance of the hollow fiber membrane has increased.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the filtration process, usually, raw water is not supplied to the hollow fiber membrane at a flow rate that maximally utilizes the capacity of the hollow fiber membrane. For this reason, even when impurities adhere to a part of the hollow fiber membrane, raw water may permeate through a portion of the hollow fiber membrane where no impurities are attached, and filtration may be performed normally. In this case, an intermembrane differential pressure similar to that when no impurities adhere to the hollow fiber membrane is measured. Therefore, in the prior art, there is a risk that an increase in the intermembrane differential pressure cannot be detected until filtration cannot be performed normally due to impurities adhering to most of the hollow fiber membrane.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide an intermembrane differential pressure prediction method and a water treatment apparatus capable of predicting a future increase in the intermembrane differential pressure of a hollow fiber membrane module.

Means for Solving the Problems

[0008] An intermembrane differential pressure prediction method according to an aspect of the present invention is an intermembrane differential pressure prediction method in a water treatment apparatus that filters raw water using a hollow fiber membrane module, and when a backwashing step of pushing treated water on the secondary side of the hollow fiber membrane module to the primary side of the hollow fiber membrane module by a pressurized medium is performed a plurality of times, in each of the plurality of backwashing steps, measuring the pressure on at least one of the primary side and the secondary side at intervals of 3 seconds or less; predicting a future increase in the intermembrane differential pressure of the hollow fiber membrane module based on differences in the measurement results of the pressure on at least one of the primary side and the secondary side between the plurality of backwashing steps; and notifying the result of the prediction.

[0009] A water treatment apparatus according to another aspect of the present invention is a water treatment apparatus that filters raw water using a hollow fiber membrane module, and when a backwashing step of pushing treated water on the secondary side of the hollow fiber membrane module to the primary side by a pressurized medium is performed multiple times, in each of the multiple backwashing steps, a measuring unit that measures the pressure on at least one of the primary side and the secondary side at intervals of 3 seconds or less, a predicting unit that predicts a future increase in the differential pressure between the membranes of the hollow fiber membrane module based on the difference in the measurement results of the pressure on at least one of the sides during the multiple backwashing steps, and a notification unit that notifies the prediction result by the predicting unit.

[0010] In the above method for predicting the differential pressure between membranes and the above water treatment apparatus, in the backwashing step, the treated water on the secondary side is pushed to the primary side by a pressurized medium. As a result, not only can the treated water be permeated at locations on the hollow fiber membrane where impurities are not attached, but it can also be made to collide with the locations where impurities are attached. As a result, the pressure applied to the treated water can be changed according to the amount of attached impurities. Therefore, according to the above method for predicting the differential pressure between membranes and the above water treatment apparatus, it is possible to measure the pressure on at least one of the primary side and the secondary side of the hollow fiber membrane module according to the amount of impurities attached to the hollow fiber membrane.

[0011] Moreover, in each of the multiple backwashing steps, the pressure on at least one of the sides is measured at intervals of 3 seconds or less, which is shorter than the normal measurement interval of the differential pressure between the membranes in the filtration step. For this reason, it is possible to grasp the detailed temporal change of the pressure on at least one of the sides in each backwashing step that ends within a few minutes.

[0012] Therefore, from the difference in the detailed temporal change between the multiple backwashing steps, it is possible to grasp the change in the amount of impurities attached to the hollow fiber membrane according to the change in the pressure on at least one of the sides. For this reason, when it is grasped that the amount of impurities attached to the hollow fiber membrane has increased, it is possible to predict that the differential pressure between the membranes will increase in the future, and the prediction result can be notified.

[0013] In the above-described inter-membrane differential pressure prediction method, in each of the plurality of backwashing steps, at least the pressure on the secondary side is measured at the interval, and based on the difference between the plurality of backwashing steps in the reaching point of the pressure on the secondary side that instantaneously increased immediately after the start of the backwashing step, the future increase in the inter-membrane differential pressure may be predicted.

[0014] Immediately after the start of the backwashing step, the treated water on the secondary side is pushed by the pressurized medium and flows into the primary side. At this time, the permeation of the treated water through the hollow fiber membrane becomes the rate-determining step, and the degree to which the treated water is pressurized by the medium is greater than the permeation of the treated water to the primary side. For this reason, the pressure on the secondary side instantaneously increases immediately after the start of the backwashing step. The reaching pressure on the secondary side at the time of the increase becomes higher as the amount of impurities attached to the hollow fiber membrane is larger and the permeation resistance of the hollow fiber membrane is greater.

[0015] According to this configuration, in each of the plurality of backwashing steps, since the pressure on the secondary side of the hollow fiber membrane module is measured at intervals of 3 seconds or less, the reaching point of the pressure on the secondary side that instantaneously increased immediately after the start of each backwashing step can be detected. Therefore, from the difference between the plurality of backwashing steps at this reaching point, the amount of impurities attached to the hollow fiber membrane and the change in the permeation resistance of the hollow fiber membrane can be grasped. For this reason, when it is grasped that the amount of impurities attached to the hollow fiber membrane is increasing and the permeation resistance of the hollow fiber membrane is increasing, the future increase in the inter-membrane differential pressure can be appropriately predicted.

[0016] In the above-described inter-membrane differential pressure prediction method, in each of the plurality of backwashing steps, at least the pressure on the secondary side is measured at the interval, and based on the difference between the plurality of backwashing steps in the time from the start point of the backwashing step until the pressure on the secondary side stabilizes at the pressure of the medium, the future increase in the inter-membrane differential pressure may be predicted.

[0017] In the backwashing process, when the extrusion of the treated water on the secondary side to the primary side is completed, the secondary side is filled with the pressurized medium, and the pressure on the secondary side stabilizes at the pressure of the medium. Here, the greater the amount of impurities attached to the hollow fiber membrane and the greater the permeation resistance of the hollow fiber membrane, the longer the time required for all the treated water on the secondary side to be extruded to the primary side. Therefore, the time from the start of the backwashing process until the pressure on the secondary side stabilizes at the pressure of the medium becomes longer as the amount of impurities attached to the hollow fiber membrane increases and the permeation resistance of the hollow fiber membrane becomes greater.

[0018] According to this configuration, in each of the multiple backwashing processes, since the pressure on the secondary side of the hollow fiber membrane module is measured at intervals of 3 seconds or less, the time from the start of each backwashing process until the pressure on the secondary side stabilizes at the pressure of the medium can be detected. Therefore, from the differences in this time among multiple backwashing processes, the change in the amount of impurities attached to the hollow fiber membrane and the permeation resistance of the hollow fiber membrane can be grasped. For this reason, when it is grasped that the amount of impurities attached to the hollow fiber membrane is increasing and the permeation resistance of the hollow fiber membrane is increasing, it is possible to appropriately predict that the transmembrane differential pressure will increase.

[0019] In the above transmembrane differential pressure prediction method, in each of the multiple backwashing processes, at least the pressure on the primary side is measured at the above intervals, and based on the differences in the reaching points of the pressure on the primary side that instantaneously increases immediately after the start of the backwashing process among the multiple backwashing processes, the future increase in the transmembrane differential pressure may be predicted.

[0020] Immediately after the backwashing process is started and the treated water on the secondary side is extruded to the primary side, the pressure on the primary side instantaneously increases. At this time, the greater the amount of impurities attached to the hollow fiber membrane and the greater the permeation resistance of the hollow fiber membrane, the slower the speed at which the treated water on the secondary side is extruded to the primary side, and the reaching pressure on the primary side decreases.

[0021] According to this configuration, in each of the multiple backwashing steps, the pressure on the primary side of the hollow fiber membrane module is measured at intervals of 3 seconds or less. Therefore, it is possible to detect the reaching point of the pressure on the primary side that instantaneously increases immediately after the start of each backwashing step. Accordingly, from the differences in the reaching points among the multiple backwashing steps, it is possible to grasp the amount of impurities attached to the hollow fiber membrane and the change in the permeation resistance of the hollow fiber membrane. For this reason, when it is grasped that the amount of impurities attached to the hollow fiber membrane is increasing and the permeation resistance of the hollow fiber membrane is increasing, it is possible to appropriately predict that the differential pressure between the membranes will increase.

[0022] In the above prediction method, in each of the multiple backwashing steps, at least the pressure on the primary side is measured at the intervals, and based on the differences among the multiple backwashing steps in the time from the start of the backwashing step until the pressure on the primary side stabilizes at a predetermined end pressure indicating the end of the extrusion of the treated water on the secondary side, the future increase in the differential pressure between the membranes may be predicted.

[0023] Immediately after the backwashing step is started and the treated water on the secondary side is extruded to the primary side, the pressure on the primary side instantaneously increases. Thereafter, the greater the amount of impurities attached to the hollow fiber membrane and the greater the permeation resistance of the hollow fiber membrane, the slower the speed at which the treated water is extruded to the primary side, and the longer the time required to complete the extrusion of the treated water on the secondary side.

[0024] According to this configuration, in each of the multiple backwashing steps, the pressure on the primary side of the hollow fiber membrane module is measured at intervals of 3 seconds or less. Therefore, it is possible to detect the time from the start of each backwashing step until the pressure on the primary side stabilizes at the end pressure. Accordingly, from the differences in this time among the multiple backwashing steps, it is possible to grasp the amount of impurities attached to the hollow fiber membrane and the change in the permeation resistance of the hollow fiber membrane. For this reason, when it is grasped that the amount of impurities attached to the hollow fiber membrane is increasing and the permeation resistance of the hollow fiber membrane is increasing, it is possible to appropriately predict that the differential pressure between the membranes will increase.

[0025] In the above prediction method, for the plurality of backwashing steps, the time from the start point of the backwashing step until the pressure on the primary side or the secondary side that instantaneously rises immediately after the start of the backwashing step reaches the reaching point, the time from when the pressure on the primary side or the secondary side that instantaneously rises immediately after the start of the backwashing step reaches the reaching point until it stabilizes, and the time from the start point of the backwashing step until the pressure on the primary side or the secondary side stabilizes, an integrated value of the difference between the pressure on the secondary side and the pressure on the primary side at any one of these times is calculated, and based on the difference in the integrated value between the plurality of backwashing steps, the future increase in the differential pressure between the membranes may be predicted.

[0026] The inventor has found through test operation that even when the difference between the pressure on the secondary side and the pressure on the primary side during the filtration step is substantially constant, whether the amount of impurities attached to the hollow fiber membrane is more or less than a predetermined amount, the integrated value of the difference at the time from the start point of the backwashing step until the pressure on the primary side or the secondary side stabilizes is significantly different. Further, the inventor has conducted further test operations and found that the integrated value at the time from the start point of the backwashing step until the pressure on the primary side or the secondary side that instantaneously rises immediately after the start of the backwashing step reaches the reaching point and the time from when the pressure on the primary side or the secondary side that instantaneously rises immediately after the start of the backwashing step reaches the reaching point until it stabilizes is also significantly different depending on whether the amount of impurities attached to the hollow fiber membrane is more or less than a predetermined amount.

[0027] Therefore, according to this configuration, the change in the amount of impurities attached to the hollow fiber membrane can be appropriately grasped by the difference in the integrated value of the difference between the pressure on the secondary side and the pressure on the primary side at the above three times between a plurality of backwashing steps. For this reason, when it is grasped that the amount of impurities attached to the hollow fiber membrane is increasing, it is possible to appropriately predict that the permeation resistance of the hollow fiber membrane increases and the differential pressure between the membranes rises.

[0028] Regarding the multiple backwashing steps, a pressure reaching point of either the primary side or the secondary side that instantaneously rises immediately after the start of the backwashing step is detected, and based on the difference in the difference between the pressure on the secondary side and the pressure on the primary side when either pressure reaches the reaching point among the multiple backwashing steps, a future increase in the differential pressure across the membrane may be predicted.

[0029] According to this configuration, regarding multiple backwashing steps, since the pressure on at least one of the primary side and the secondary side of the hollow fiber membrane module is measured at intervals of 3 seconds or less, a pressure reaching point of either the primary side or the secondary side that instantaneously rises immediately after the start of the backwashing step can be detected. That is, even if the impurities are such that they are peeled off from the surface of the hollow fiber membrane by the force that pushes the treated water from the secondary side to the primary side in the backwashing step, the appropriate pressure before the decrease due to the peeling off of the impurities can be detected.

[0030] As a result, by using the difference in the difference between the pressure on the secondary side and the pressure on the primary side at the detection time point, a change in the amount of impurities attached to the hollow fiber membrane can be appropriately grasped. Therefore, when it is grasped that the amount of impurities attached to the hollow fiber membrane is increasing, an increase in the permeation resistance of the hollow fiber membrane and an increase in the differential pressure across the membrane can be appropriately predicted.

[0031] A method for predicting the differential pressure across the membrane according to another aspect of the present invention is a prediction method in a water treatment apparatus that filters raw water using a hollow fiber membrane module. When a water filling step of filling the inside of the hollow fiber membrane module with raw water is performed multiple times, in each of the multiple water filling steps, the pressure on the primary side of the hollow fiber membrane module is measured at intervals of 3 seconds or less, and based on the difference in the time from the start of the water filling step to the inflection point of the change in the pressure on the primary side in the measurement result of the pressure on the primary side among the multiple water filling steps, predicting a future increase in the differential pressure across the hollow fiber membrane module, and notifying the result of the prediction.

[0032] The water treatment apparatus according to another aspect of the present invention is a water treatment apparatus that filters raw water using a hollow fiber membrane module. When a water filling step of filling the inside of the hollow fiber membrane module with raw water is performed a plurality of times, in each of the plurality of water filling steps, a measurement unit that measures the pressure on the primary side of the hollow fiber membrane module at intervals of 3 seconds or less, and based on the difference between the plurality of water filling steps in the time from the start of the water filling step to the inflection point of the change in the pressure on the primary side in the measurement result of the pressure on the primary side, a prediction unit that predicts the future increase in the differential pressure between the membranes of the hollow fiber membrane module, and a notification unit that notifies the result of the prediction.

[0033] When the water filling step is started and raw water flows into the inside of the hollow fiber membrane module, the pressure on the primary side gradually increases due to the head pressure. Then, when the inside of the hollow fiber membrane module approaches a full water state, the pressure on the primary side rapidly increases. Therefore, the time from the start of the water filling step to the inflection point of the change in the pressure on the primary side becomes shorter as the amount of impurities accumulated inside the hollow fiber membrane module is larger and the effective volume inside the hollow fiber membrane module is smaller.

[0034] Also, it is presumed that the larger the amount of impurities accumulated inside the hollow fiber membrane module and the smaller the effective volume inside the hollow fiber membrane module, the larger the amount of impurities attached to the hollow fiber membrane, that is, it is presumed that the differential pressure between the membranes will increase in the future.

[0035] In the above-described differential pressure between membranes prediction method and the above-described water treatment apparatus, in the water filling step, the pressure on the primary side of the hollow fiber membrane module when the inside of the hollow fiber membrane module is filled with raw water is measured. Therefore, in the above-described differential pressure between membranes prediction method and the above-described water treatment apparatus, the pressure on the primary side of the hollow fiber membrane module can be measured according to the amount of impurities accumulated inside the hollow fiber membrane module.

[0036] Moreover, in the above-described inter-membrane differential pressure prediction method and the above-described water treatment apparatus, in each of a plurality of water filling steps, the pressure on the primary side of the hollow fiber membrane module is measured at intervals of 3 seconds or less, which is shorter than the normal measurement interval of the inter-membrane differential pressure in the filtration step. Therefore, it is possible to grasp the detailed temporal change of the pressure on the primary side of the hollow fiber membrane module in each water filling step that ends within several minutes.

[0037] Therefore, from the differences between a plurality of water filling steps in this detailed temporal change, it is possible to grasp the change in the accumulation amount of impurities inside the hollow fiber membrane module according to the change in the pressure on the primary side of the hollow fiber membrane module.

[0038] Specifically, from the difference in time from the start of the water filling step to the inflection point of the change in the pressure on the primary side between a plurality of water filling steps, it is possible to grasp the change in the accumulation amount of impurities and the effective volume inside the hollow fiber membrane module. Therefore, when it is grasped that the accumulation amount of impurities inside the hollow fiber membrane module is increasing and the effective volume inside the hollow fiber membrane module is decreasing, it is possible to appropriately predict that the amount of impurities attached to the hollow fiber membrane is increasing, that is, the situation where the inter-membrane differential pressure will increase in the future, and the prediction result can be notified.

[0039] The inter-membrane differential pressure prediction method according to another aspect of the present invention is a prediction method in a water treatment apparatus that filters raw water using a hollow fiber membrane module. When a drainage step of draining drain water containing turbidity components peeled off from the hollow fiber membrane is performed a plurality of times, in each of the plurality of drainage steps, the pressure on the primary side of the hollow fiber membrane module is measured at intervals of 3 seconds or less, and based on the difference between the plurality of drainage steps in the time from the start of the drainage step to when the pressure on the primary side becomes constant in the measurement result of the pressure on the primary side, predicting a future increase in the inter-membrane differential pressure of the hollow fiber membrane module, and notifying the result of the prediction.

[0040] A water treatment apparatus according to another aspect of the present invention is a water treatment apparatus that filters raw water using a hollow fiber membrane module. When a drainage step of draining drain water containing turbidity components peeled off from the hollow fiber membrane is performed multiple times, in each of the multiple drainage steps, a measuring unit that measures the pressure on the primary side of the hollow fiber membrane module at intervals of 3 seconds or less, and based on the difference between the multiple drainage steps in the time from the start of the drainage step until the pressure on the primary side becomes constant in the measurement result of the pressure on the primary side, a prediction unit that predicts a future increase in the differential pressure between the membranes of the hollow fiber membrane module, and a notification unit that notifies the result of the prediction.

[0041] When the drainage of the drain water inside the hollow fiber membrane module is completed in the drainage step, the pressure on the primary side becomes stable. Therefore, the time from the start of the drainage step until the pressure on the primary side becomes constant becomes shorter as the amount of impurities accumulated inside the hollow fiber membrane module is larger and the effective volume inside the hollow fiber membrane module is smaller.

[0042] Also, it is presumed that the larger the amount of impurities accumulated inside the hollow fiber membrane module and the smaller the effective volume inside the hollow fiber membrane module, the larger the amount of impurities attached to the hollow fiber membrane, that is, it is presumed that the differential pressure between the membranes will increase in the future.

[0043] In the above differential pressure between membranes prediction method and the above water treatment apparatus, in the drainage step, the pressure on the primary side of the hollow fiber membrane module when the drain water inside the hollow fiber membrane module is discharged is measured. Therefore, in the above prediction method and the above water treatment apparatus, the pressure on the primary side of the hollow fiber membrane module can be measured according to the amount of impurities accumulated inside the hollow fiber membrane module.

[0044] Moreover, in the above-described inter-membrane differential pressure prediction method and the water treatment apparatus, in each of a plurality of drainage steps, the pressure on the primary side inside the hollow fiber membrane module is measured at intervals of 3 seconds or less, which is shorter than the normal measurement interval of the inter-membrane differential pressure in the filtration step. Therefore, it is possible to grasp the detailed temporal change of the pressure on the primary side of the hollow fiber membrane module in each drainage step that ends within several minutes.

[0045] Therefore, from the differences between a plurality of drainage steps in this detailed temporal change, it is possible to grasp the change in the accumulation amount of impurities inside the hollow fiber membrane module according to the change in the pressure on the primary side of the hollow fiber membrane module.

[0046] Specifically, from the difference in time from the start of the drainage step until the pressure on the primary side becomes constant between a plurality of drainage steps, it is possible to grasp the change in the accumulation amount of impurities and the effective volume inside the hollow fiber membrane module. Therefore, when it is grasped that the accumulation amount of impurities inside the hollow fiber membrane module is increasing and the effective volume inside the hollow fiber membrane module is decreasing, it is possible to appropriately predict that the amount of impurities attached to the hollow fiber membrane is increasing, that is, the situation where the inter-membrane differential pressure will increase in the future, and the prediction result can be notified.

Advantages of the Invention

[0047] As is clear from the above description, according to the present invention, it is possible to provide an inter-membrane differential pressure prediction method and a water treatment apparatus capable of predicting an increase in the future inter-membrane differential pressure of a hollow fiber membrane module.

Brief Description of the Drawings

[0048]

Figure 1

Figure 2

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Figure 8

Embodiments for Carrying Out the Invention

[0049] (Embodiment) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0050] First, the configuration of the water treatment apparatus 1 according to the embodiment of the present invention will be described with reference to FIG. 1. As shown in FIG. 1, the water treatment apparatus 1 mainly includes a hollow fiber membrane module 10, a raw water supply unit 20, a bubbling air supply unit 30, and a backwashing air supply unit 40.

[0051] The hollow fiber membrane module 10 includes a hollow fiber membrane bundle having a plurality of hollow fiber membranes 11 whose upper ends are fixed to a fixing member 13, a housing 12, a water guide pipe 14 extending vertically inside the hollow fiber membrane bundle, and a diffuser plate 15. Inside the housing 12, the hollow fiber membrane bundle, the fixing member 13, and the diffuser plate 15 are accommodated. The space inside the housing 12 is partitioned into a raw water space S1 and a treated water space S2 by the fixing member 13. The hollow fiber membranes 11, the water guide pipe 14, and the diffuser plate 15 are accommodated in the raw water space S1.

[0052] As shown in Fig. 1, an outlet 12A for treated water (filtered water) is provided at the upper part of the housing 12 so as to face the treated water space S2. An air vent 12B is provided at a side part of the housing 12 (a part above the center in the longitudinal direction) so as to face the raw water space S1. An air supply port 12C and a drain port 12D are provided at the lower part of the housing 12 so as to face the raw water space S1. The ratio of the inner diameter of the housing 12 to the inner diameters of these pipe connection ports (the outlet 12A, the air vent 12B, the air supply port 12C, and the drain port 12D) is 1.3 or more and 12 or less, preferably 2.5 or more and 12 or less, and more preferably 3.0 or more and 6.0 or less. Here, the inner diameter of the housing 12 referred to herein is the inner diameter in the cross section in the direction orthogonal to the longitudinal direction of the housing 12.

[0053] The water conduit 14 is for supplying raw water and air to the raw water space S1. As shown in Fig. 1, the upper end of the water conduit 14 is fixed to the fixing member 13 and its end face is blocked, and the lower end thereof protrudes below the lower part of the housing 12. A raw water inlet 14A and an air inlet 14B are respectively provided at the lower end. Further, a number of holes 14C for jetting at least one of raw water and air from the inside of the water conduit 14 toward the raw water space S1 are formed in the water conduit 14.

[0054] The air diffuser plate 15 is for dispersing air in the raw water space S1. The air diffuser plate 15 has a disk shape that spreads in the radial direction of the hollow fiber membrane bundle and is installed below the lower end of the hollow fiber membrane 11. A plurality of vent holes (not shown) are formed in the air diffuser plate 15 at intervals in the radial direction. The air supplied into the housing 12 from the air supply port 12C is dispersed toward the hollow fiber membrane bundle through the vent holes of the air diffuser plate 15.

[0055] As shown in Fig. 1, the upstream end of the treated water pipe 50 is connected to the outlet 12A of the housing 12. The downstream end of the treated water pipe 50 is connected to the inlet of a treated water tank (not shown). A treated water valve 51 (on-off valve) and a flow meter 52 on the downstream side thereof are respectively installed in the treated water pipe 50. The diameter of the treated water pipe 50 is smaller than the diameter of the housing 12.

[0056] The upstream end of the drain pipe 53 is connected to the drain outlet 12D of the housing 12, and a drain valve 54 (on-off valve) is installed in the drain pipe 53. The diameter of the drain pipe 53 is smaller than the diameter of the housing 12.

[0057] One end of the air vent pipe 55 is connected to the air vent 12B of the housing 12. The other end side of the air vent pipe 55 branches into two. That is, the air vent pipe 55 includes a first branch portion 55A, a second branch portion 55B, and a connection portion 55C. One end of the connection portion 55C is connected to the air vent 12B, and the other end is connected to the first branch portion 55A and the second branch portion 55B. The first branch portion 55A is open to the atmosphere, and the second branch portion 55B is connected to a portion of the drain pipe 53 downstream of the drain valve 54. An air vent valve 56 (on-off valve) is installed in the connection portion 55C. The diameter of the air vent pipe 55 is smaller than the diameter of the housing 12.

[0058] As shown in FIG. 1, the treated water pipe 50 and the drain pipe 53 are connected to each other by a pressure relief pipe 57. One end of the pressure relief pipe 57 is connected to a portion of the treated water pipe 50 upstream of the treated water valve 51, and the other end of the pressure relief pipe 57 is connected to a portion of the drain pipe 53 downstream of the connection portion of the air vent pipe 55. A pressure relief valve 58 (on-off valve) is installed in the pressure relief pipe 57. The diameter of the pressure relief pipe 57 is smaller than the diameter of the housing 12.

[0059] The raw water supply unit 20 includes a raw water pipe 21, a raw water pump 22 and a raw water valve 23 installed in the raw water pipe 21. The upstream end of the raw water pipe 21 is connected to the outlet of a raw water tank (not shown), and the downstream end is connected to the raw water inlet 14A of the water guide pipe 14. The diameter of the raw water pipe 21 is smaller than the diameter of the housing 12. The raw water valve 23 is an on-off valve and is installed downstream of the raw water pump 22 in the raw water pipe 21.

[0060] The air supply unit 30 for bubbling includes an air pipe 31, a first air valve 32, a second air valve 33, and a flow meter 34. The downstream end side of the air pipe 31 is branched, and each branched portion is connected to the air supply port 12C of the housing 12 and the air inlet 14B of the water conduit 14, respectively. The diameter of the air pipe 31 is smaller than the diameter of the housing 12. The first air valve 32 and the second air valve 33 are on-off valves and are respectively installed at each branched portion of the air pipe 31. The upstream end of the air pipe 31 is connected to an air compressor (not shown).

[0061] The air supply unit 40 for backwashing includes an air pipe 41 and an air valve 42 (on-off valve) installed on the air pipe 41. The upstream end of the air pipe 41 is connected to an air compressor (not shown), and the downstream end is connected to a portion of the treated water pipe 50 upstream of the connection portion of the pressure relief pipe 57. The diameter of the air pipe 41 is smaller than the diameter of the housing 12.

[0062] The water treatment apparatus 1 further includes a measuring unit 60 that measures the pressure on at least one of the primary side and the secondary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less (for example, intervals of 2 seconds or less or 1 second or less) in the backwashing process of the hollow fiber membrane module 10. The measuring unit 60 in the present embodiment includes a primary side pressure sensor 61 that measures the pressure on the primary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less, and a secondary side pressure sensor 62 that measures the pressure on the secondary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less.

[0063] As shown in FIG. 1, the primary side pressure sensor 61 is installed in a portion of the raw water pipe 21 between the raw water valve 23 and the raw water inlet 14A. Incidentally, the primary side pressure sensor 61 may be installed at a position extending from the housing 12 in the water conduit 14 or facing the raw water space S1 in the housing 12.

[0064] The secondary pressure sensor 62 is installed at the connection part between the treated water pipe 50 and the air pipe 41. The primary pressure sensor 61 and the secondary pressure sensor 62 in this embodiment perform pressure measurement at intervals of 0.1 second or less, and the measurement data is sent to the control unit 70 described later and stored. That is, each measurement data is stored as logging data.

[0065] In addition to the primary pressure sensor 61 and the secondary pressure sensor 62, an air vent pressure sensor may be provided. The air vent pressure sensor is installed at the connection part 55C in the air vent pipe 55. The air vent pressure sensor performs pressure measurement at intervals of 0.1 second or more and 3 seconds or less, and each measurement data is sent to the control unit 70 described later and stored. That is, the measurement data of the air vent pressure sensor is stored as logging data indicating the pressure on the primary side of the hollow fiber membrane module 10. However, since there are problems such as the more the number of pressure sensors increases, the more laborious the analysis becomes and the cost increases, it is desirable to omit the air vent pressure sensor and perform data analysis using the data from the primary pressure sensor 61 and the secondary pressure sensor 62.

[0066] The water treatment apparatus 1 further includes a control unit 70. The control unit 70 is configured by a microcomputer including a CPU, a RAM, a ROM, and the like. The control unit 70 controls the execution of the filtration operation. Specifically, the control unit 70 sequentially executes each process constituting the operation cycle of filtration according to the sequence information stored in the ROM or the like. When starting the execution of each process, the control unit 70 performs drive control of peripheral devices and opening / closing control of valves according to the process information stored in the ROM or the like corresponding to the process to be executed.

[0067] The functions of the control unit 70 include a prediction unit 71 and a notification unit 72. The prediction unit 71 predicts an increase in the differential pressure between membranes of the hollow fiber membrane module 10 based on the result of pressure measurement by the measurement unit 60. The differential pressure between membranes of the hollow fiber membrane module 10 is the differential pressure between the pressure on the secondary side and the pressure on the primary side of the hollow fiber membrane module 10, and is obtained by subtracting the pressure on the primary side from the pressure on the secondary side. The notification unit 72 notifies the result of the evaluation by the prediction unit 71.

[0068] Further, the prediction unit 71 and the notification unit 72 may not be realized as a function of the control unit 70. The control unit 70, the prediction unit 71, and the notification unit 72 may each be configured by an individual microcomputer.

[0069] FIG. 2 shows each step of the water treatment method implemented using the water treatment apparatus 1, and also shows the on / off state of the raw water pump 22 and the open / closed state of each valve in each step. The circles in FIG. 2 indicate the on state of the raw water pump 22 or the open state of the valve, and the blanks indicate the off state of the raw water pump 22 or the closed state of the valve.

[0070] First, in the first water filling step, the raw water pump 22 operates, and the raw water valve 23 and the air vent valve 56 are each opened. As a result, raw water is supplied into the water conduit 14 through the raw water pipe 21, and the raw water is supplied from the hole 14C to the raw water space S1.

[0071] When the first water filling step ends, it proceeds to the filtration step. In the filtration step, the air vent valve 56 is closed and the treated water valve 51 is opened. The raw water permeates the membrane wall from the outer surface to the inner surface of the hollow fiber membrane 11 and flows into the treated water space S2 through the hollow portion of the membrane. Then, the treated water flows out of the housing 12 through the outlet 12A and is collected in a treated water tank (not shown) through the treated water pipe 50.

[0072] After the filtration step, physical cleaning is performed to remove impurities adhering to the outer surface of the hollow fiber membrane 11 during filtration. The physical cleaning includes a reverse washing preparation step (pressure release step), a reverse washing step, an air venting step, a second water filling step, a diffuser plate bubbling step, a third water filling step, a water conduit bubbling step, a drainage step, and a pressure release step.

[0073] First, in the reverse washing preparation step (pressure release step), the raw water pump 22 is switched from on to off.

[0074] Next, in the backwashing process, the raw water valve 23 and the treated water valve 51 are closed, and the air valve 42 and the drain valve 54 are opened. That is, simultaneously with the opening of the air valve 42, the pressure of the air pressurized by the compressor is instantaneously applied to the treated water on the secondary side of the hollow fiber membrane module 10. As a result, the treated water on the secondary side of the hollow fiber membrane module 10 is pressurized by the air (medium) pressurized to a predetermined pressure, and the treated water permeates the membrane wall from the inner surface to the outer surface of the hollow fiber membrane 11. Thereby, the impurities adhering to the outer surface of the hollow fiber membrane 11 are in a state where they are easily peeled off. At this time, since the primary side pressure sensor 61 and the secondary side pressure sensor 62 perform pressure measurement at intervals of 3 seconds or less, the pressure in the state after the hollow fiber membrane 11 is pressurized from the inner surface and before the impurities on the membrane surface are easily peeled off can also be detected. The above-mentioned predetermined pressure is preferably 30 kPa to 500 kPa, more preferably 50 kPa to 300 kPa, and most preferably 50 kPa to 200 kPa.

[0075] In the backwashing process, the secondary side pressure sensor 62 measures the pressure on the secondary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less. Thereby, logging data (Figure 3) showing the time change of the secondary side pressure of the hollow fiber membrane module 10 during the backwashing process is obtained. In Figure 3, the horizontal axis represents time, and the vertical axis represents the secondary side pressure of the hollow fiber membrane module 10. The graph G31 in Figure 3 shows the time change of the secondary side pressure of the hollow fiber membrane module 10 during the backwashing process immediately before the most recent backwashing process. The graph G32 in Figure 3 shows the time change of the secondary side pressure of the hollow fiber membrane module 10 during the most recent backwashing process. That is, the graph G31 shows the time change of the secondary side pressure during the backwashing process one time before the graph G32.

[0076] Immediately after the start of the backwashing process, the treated water on the secondary side is rapidly pushed by the pressurized air and flows into the primary side. At this time, the permeation of the treated water through the hollow fiber membrane 11 becomes the rate-determining step, and the degree to which the treated water is pressurized by the air is greater than the permeation of the treated water to the primary side. Therefore, the pressure on the secondary side increases immediately after the start of the backwashing process. Then, a part of the impurities adhering to the surface of the hollow fiber membrane 11 is peeled off or becomes easily peeled off by the force pushing the treated water to the primary side, so that the pressure on the secondary side instantaneously decreases or is maintained. Thereafter, the pressure on the secondary side increases again by the pressurization with air. In this way, the pressure on the secondary side instantaneously increases immediately after the start of the backwashing process. The reaching pressure on the secondary side at the time of the increase becomes higher as the amount of impurities adhering to the hollow fiber membrane 11 is larger and the permeation resistance of the hollow fiber membrane 11 is greater.

[0077] The prediction unit 71 refers to the logging data stored in the control unit 70, and predicts the future increase in the differential pressure between the membranes of the hollow fiber membrane module 10 based on the difference between the reaching points of the pressure on the secondary side that instantaneously increases immediately after the start of the backwashing process among multiple backwashing processes. The multiple backwashing processes may be, for example, the most recent backwashing process and the backwashing process performed immediately before the most recent backwashing process, or the most recent backwashing process and multiple backwashing processes performed in the past more than the most recent backwashing process.

[0078] Specifically, when the reaching pressure on the secondary side immediately after the start of the backwashing process shows an upward trend among multiple backwashing processes, the prediction unit 71 predicts that the differential pressure between the membranes of the hollow fiber membrane module 10 will increase in the future because the amount of impurities adhering to the hollow fiber membrane 11 increases and the permeation resistance of the hollow fiber membrane 11 increases.

[0079] In the example of FIG. 3, the reaching pressure P32 on the secondary side immediately after the start of the most recent backwashing process is higher than the reaching pressure P31 on the secondary side immediately after the start of the backwashing process immediately before the most recent backwashing process. Therefore, the prediction unit 71 predicts that the differential pressure between the membranes of the hollow fiber membrane module 10 will increase in the future.

[0080] Also, in the backwashing process, when the extrusion of the treated water on the secondary side to the primary side is completed, the secondary side is filled with pressurized air, and the pressure on the secondary side stabilizes at the air pressure. Here, the greater the amount of impurities attached to the hollow fiber membrane 11 and the greater the permeation resistance of the hollow fiber membrane 11, the longer the time required for all the treated water on the secondary side to be extruded to the primary side. Therefore, the time from the start of the backwashing process until the pressure on the secondary side stabilizes at the air pressure becomes longer as the amount of impurities attached to the hollow fiber membrane 11 increases and the permeation resistance of the hollow fiber membrane 11 increases.

[0081] Note that the pressure stabilizing means, for example, that the rising pressure reaches an inflection point where the slope of the pressure rise decreases, the decreasing pressure reaches an inflection point where the slope of the pressure decrease increases, or the rising or decreasing pressure continues within a predetermined allowable range for a predetermined time or more and fluctuates.

[0082] Therefore, the prediction unit 71 may refer to the logging data stored in the control unit 70 and predict the future increase in the differential pressure between the membranes of the hollow fiber membrane module 10 based on the differences in the time from the start of the backwashing process until the pressure on the secondary side stabilizes at the air pressure in multiple backwashing processes.

[0083] Specifically, it is assumed that the time from the start of the backwashing process until the pressure on the secondary side stabilizes at the air pressure shows an increasing trend among multiple backwashing processes. In this case, since the prediction unit 71 determines that the amount of impurities attached to the hollow fiber membrane 11 is increasing and the permeation resistance of the hollow fiber membrane 11 is increasing, it predicts that the differential pressure between the membranes of the hollow fiber membrane module 10 will increase in the future.

[0084] In the example of FIG. 3, the time t32 from the start of the most recent backwashing process until the pressure on the secondary side stabilizes at the air pressure is longer than the time t31 from the start of the backwashing process immediately before the most recent backwashing process until the pressure on the secondary side stabilizes at the air pressure. Therefore, the prediction unit 71 predicts that the differential pressure between the membranes of the hollow fiber membrane module 10 will increase in the future.

[0085] Also, in the backwashing process, the primary-side pressure sensor 61 measures the pressure on the primary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less. As a result, logging data (Figure 4) showing the temporal change in the primary-side pressure of the hollow fiber membrane module 10 during the backwashing process is obtained.

[0086] In addition, as described above, it is assumed that the pressure on the primary side of the hollow fiber membrane module 10 is measured by the air vent pressure sensor at intervals of 3 seconds or less. In this case, the prediction unit 71 may use, as logging data indicating the pressure on the primary side of the hollow fiber membrane module 10, data indicating the average value of the pressure on the primary side shown by the logging data received from each of the primary-side pressure sensor 61 and the air vent pressure sensor.

[0087] In Figure 4, the horizontal axis represents time, and the vertical axis represents the primary-side pressure of the hollow fiber membrane module 10. The graph G41 in Figure 4 shows the temporal change in the primary-side pressure of the hollow fiber membrane module 10 during the backwashing process immediately before the most recent backwashing process. The graph G42 in Figure 4 shows the temporal change in the primary-side pressure of the hollow fiber membrane module 10 during the most recent backwashing process.

[0088] As shown in Figure 4, immediately after the backwashing process is started and the treated water on the secondary side is pushed out to the primary side, since the diameter of the drain pipe 53 is smaller than that of the housing 12, the pressure on the primary side instantaneously increases due to the pipeline resistance generated when the raw water on the primary side flows into the drain pipe 53. At this time, the greater the amount of impurities attached to the hollow fiber membrane 11 and the greater the permeation resistance of the hollow fiber membrane 11, the slower the speed at which the treated water on the secondary side is pushed out to the primary side, and the lower the reaching pressure on the primary side.

[0089] Therefore, the prediction unit 71 may refer to the logging data stored in the control unit 70 and predict the future increase in the intermembrane differential pressure of the hollow fiber membrane module 10 based on the differences in the reaching points of the pressure on the primary side that instantaneously increases immediately after the start of the backwashing process in multiple backwashing processes.

[0090] Specifically, in multiple backwashing steps, it is assumed that the primary-side reaching pressure immediately after the start of the backwashing step shows a decreasing trend. In this case, since the amount of impurities attached to the hollow fiber membrane 11 is increasing and the permeation resistance of the hollow fiber membrane 11 is increasing, the prediction unit 71 may predict that the intermembrane differential pressure of the hollow fiber membrane module 10 will increase in the future.

[0091] In the example of FIG. 4, the primary-side reaching pressure P42 immediately after the start of the most recent backwashing step is lower than the primary-side reaching pressure P41 immediately after the start of the backwashing step immediately before the most recent backwashing step. Therefore, the prediction unit 71 predicts that the intermembrane differential pressure of the hollow fiber membrane module 10 will increase in the future.

[0092] Also, immediately after the backwashing step is started and the treated water on the secondary side is pushed out to the primary side and the pressure on the primary side instantaneously increases, the greater the amount of impurities attached to the hollow fiber membrane 11 and the greater the permeation resistance of the hollow fiber membrane 11, the slower the speed at which the treated water is pushed out to the primary side, and the longer the time required to complete the pushing out of the treated water on the secondary side.

[0093] Therefore, the prediction unit 71 refers to the logging data stored in the control unit 70, and based on the difference between multiple backwashing steps in the time from the start of the backwashing step until the pressure on the primary side stabilizes at a predetermined end pressure (for example, 0 kPa) indicating the end of the pushing out of the treated water on the secondary side, may predict an increase in the future intermembrane differential pressure of the hollow fiber membrane module 10.

[0094] Specifically, in multiple backwashing steps, it is assumed that the time from the start of the backwashing step until the pressure on the primary side stabilizes at the end pressure shows an increasing trend. In this case, since the amount of impurities attached to the hollow fiber membrane 11 is increasing and the permeation resistance of the hollow fiber membrane 11 is increasing, the prediction unit 71 may predict that the intermembrane differential pressure of the hollow fiber membrane module 10 will increase in the future.

[0095] In the example of FIG. 4, the time t42 from the start of the most recent backwashing step until the primary-side pressure stabilizes at the end pressure is longer than the time t41 from the start of the backwashing step immediately preceding the most recent backwashing step until the primary-side pressure stabilizes at the end pressure. For this reason, the prediction unit 71 predicts that the differential pressure between the membranes of the hollow fiber membrane module 10 will increase in the future.

[0096] Further, the inventor conducted a test operation and used the logging data (FIGS. 5 and 6) obtained in each of the backwashing step (hereinafter, the first backwashing step) when the amount of impurities attached to the hollow fiber membrane 11 is less than a predetermined amount and the backwashing step (hereinafter, the second backwashing step) when the amount of impurities attached to the hollow fiber membrane 11 is more than a predetermined amount, and calculated the integrated value of the difference between the secondary-side pressure and the primary-side pressure over the time from the start of the backwashing step until the primary-side pressure stabilizes.

[0097] In FIGS. 5 and 6, the horizontal axis represents time, and the vertical axis represents the pressures on the primary side and the secondary side of the hollow fiber membrane module 10. The graph G51 in FIG. 5 shows the change over time of the primary-side pressure of the hollow fiber membrane module 10 in the first backwashing step. The graph G52 in FIG. 5 shows the change over time of the secondary-side pressure of the hollow fiber membrane module 10 in the first backwashing step. The graph G61 in FIG. 6 shows the change over time of the primary-side pressure of the hollow fiber membrane module 10 in the second backwashing step. The graph G62 in FIG. 6 shows the change over time of the secondary-side pressure of the hollow fiber membrane module 10 in the second backwashing step.

[0098] Next, the inventor used the logging data shown in FIG. 5 obtained in the first backwashing step to calculate the integrated value of the difference between the secondary-side pressure and the primary-side pressure over the time t50 to t51 (hereinafter, the target time) from the start time t50 of the first backwashing step until the time t51 when the primary-side pressure stabilizes. In FIG. 5, the integrated value of the difference between the secondary-side pressure and the primary-side pressure over the target time t50 to t51 corresponds to the area of the region surrounded by the dashed line indicating the start time t50 of the first backwashing step, the dashed line indicating the time t51 when the primary-side pressure stabilizes, the graph G52, and the graph G51.

[0099] Similarly, the inventor used the logging data shown in FIG. 6 obtained in the second backwashing step, and set the time t60 to t61 from the start time t60 of the second backwashing step to the time when the pressure on the primary side stabilizes as the target time, and calculated the integral value of the difference between the pressure on the secondary side and the pressure on the primary side during the target time t60 to t61.

[0100] Then, the inventor compared the measurement result of the difference between the pressure on the secondary side and the pressure on the primary side in the filtration step performed after the first backwashing step, the measurement result of the difference in the filtration step performed after the second backwashing step, and the calculation result of the integral value. As a result, the inventor found that even when the difference between the pressure on the secondary side and the pressure on the primary side during the filtration step is substantially constant, the integral value during the predetermined period is significantly different depending on whether the amount of impurities attached to the hollow fiber membrane 11 is more or less than a predetermined amount.

[0101] This is presumably because the time from the start time of the backwashing step until the pressure on the primary side, which instantaneously increased immediately after the start of the backwashing step, reaches the arrival point, and the time from when the pressure on the primary side, which instantaneously increased immediately after the start of the backwashing step, reaches the arrival point until it stabilizes, become longer as the amount of impurities attached to the hollow fiber membrane 11 increases.

[0102] Therefore, similarly, the inventor changed the target time to the time from the start time t50 of the first backwashing step until the pressure on the primary side, which instantaneously increased immediately after the start of the first backwashing step, reaches the arrival point P51, and calculated the integral value. Also, the inventor changed the target time to the time from the start time t60 of the second backwashing step until the pressure on the primary side, which instantaneously increased immediately after the start of the second backwashing step, reaches the arrival point P61, and calculated the integral value. Also in this case, the inventor obtained the same findings as above.

[0103] The inventor changed the target time to the time from when the primary pressure that instantaneously increased immediately after the start of the first backwashing process reached the reaching point P51 until it stabilized at time t51, and calculated the integral value. The inventor also changed the target time to the time from when the primary pressure that instantaneously increased immediately after the start of the second backwashing process reached the reaching point P61 until it stabilized at time t61, and calculated the integral value. Also in this case, the inventor obtained the same findings as above.

[0104] Furthermore, the inventor changed the target time to the time from the start time t50 of the first backwashing process until the secondary pressure stabilized at time t52, and calculated the integral value. The inventor also changed the target time to the time from the start time t60 of the second backwashing process until the secondary pressure stabilized at time t62, and calculated the integral value. Also in this case, the inventor obtained the same findings as above.

[0105] The inventor changed the target time to the time from the start time t50 of the first backwashing process until the secondary pressure that instantaneously increased immediately after the start of the backwashing process reached the reaching point P52, and calculated the integral value. The inventor also changed the target time to the time from the start time t60 of the second backwashing process until the secondary pressure that instantaneously increased immediately after the start of the second backwashing process reached the reaching point P62, and calculated the integral value. Also in this case, the inventor obtained the same findings as above.

[0106] The inventor changed the target time to the time from when the secondary pressure that instantaneously increased immediately after the start of the first backwashing process reached the reaching point P52 until it stabilized at time t52, and calculated the integral value. The inventor also changed the target time to the time from when the secondary pressure that instantaneously increased immediately after the start of the second backwashing process reached the reaching point P62 until it stabilized at time t62, and calculated the integral value. Also in this case, the inventor obtained the same findings as above.

[0107] The inventor also found that the greater the amount of impurities attached to the hollow fiber membrane 11, the larger the integral value at each of the above target times.

[0108] Therefore, based on the above findings obtained by the present inventor, the prediction unit 71 calculates, for a plurality of backwashing steps, the integrated value of the difference between the secondary-side pressure and the primary-side pressure at any one of the times: the time from the start point of the backwashing step until the time when the primary-side or secondary-side pressure that instantaneously increases immediately after the start of the backwashing step reaches the arrival point; the time from when the primary-side or secondary-side pressure that instantaneously increases immediately after the start of the backwashing step reaches the arrival point until it stabilizes; and the time from the start point of the backwashing step until the time when the primary-side or secondary-side pressure stabilizes. Then, the prediction unit 71 may predict the future increase in the inter-membrane differential pressure of the hollow fiber membrane module 10 based on the difference in the integrated values between the plurality of backwashing steps.

[0109] Specifically, assume that the integrated values calculated in a plurality of backwashing steps show an increasing trend. In this case, since the amount of impurities attached to the hollow fiber membrane 11 is large, the prediction unit 71 may predict that the permeation resistance of the hollow fiber membrane 11 increases and the inter-membrane differential pressure of the hollow fiber membrane module 10 will increase in the future.

[0110] Also, as described above, immediately after the start of the backwashing step, the secondary-side pressure instantaneously increases immediately after the start of the backwashing step. At this time, the secondary-side arrival pressure becomes higher as the amount of impurities attached to the hollow fiber membrane 11 increases. Also, as the secondary-side pressure increases, the permeation rate of the treated water increases, and the fouling components attached to the outer surface of the hollow fiber membrane 11 are likely to peel off. Then, when a part of the fouling components attached to the outer surface of the hollow fiber membrane 11 is peeled off, the secondary-side pressure instantaneously decreases but increases again by pressurization with air. As a result, the speed at which the treated water is pushed out to the primary side increases.

[0111] On the other hand, immediately after the treated water on the secondary side is pushed out to the primary side, when the raw water on the primary side flows into the drain pipe 53, the pressure on the primary side instantaneously increases due to the pipeline resistance generated at that time. At this time, the greater the amount of impurities attached to the hollow fiber membrane 11, the slower the speed at which the treated water on the secondary side is pushed out to the primary side. Therefore, the reaching pressure on the primary side that instantaneously increases immediately after the start of the backwashing process becomes lower as the amount of impurities attached to the hollow fiber membrane 11 increases. Thereafter, when a part of the impurities attached to the outer surface of the hollow fiber membrane 11 is peeled off and the speed at which the treated water is pushed out to the primary side increases, the speed at which the water on the primary side is discharged also increases, and the pressure on the primary side rapidly decreases.

[0112] That is, immediately before the pressure on either the primary side or the secondary side that instantaneously increases immediately after the start of the backwashing process reaches the reaching point and a part of the impurities attached to the outer surface of the hollow fiber membrane 11 is peeled off, the difference between the pressure on the secondary side and the pressure on the primary side becomes larger as the amount of impurities attached to the hollow fiber membrane 11 increases.

[0113] Therefore, the prediction unit 71 may refer to the logging data stored in the control unit 70 and detect the reaching point of the pressure on either the primary side or the secondary side that instantaneously increases immediately after the start of the backwashing process for a plurality of backwashing processes. Then, the prediction unit 71 may predict the future increase in the differential pressure between the membranes of the hollow fiber membrane module 10 based on the difference between the differential pressures between the secondary side and the primary side at the time when any of the pressures reaches the reaching point during the plurality of backwashing processes.

[0114] Specifically, assume that the difference between the pressure on the secondary side and the pressure on the primary side at the time when any of the pressures that instantaneously increase immediately after the start of the backwashing process reaches the reaching point during the plurality of backwashing processes shows an upward trend. In this case, since the situation is that the amount of impurities attached to the hollow fiber membrane 11 is increasing, the prediction unit 71 may predict that the permeation resistance of the hollow fiber membrane 11 increases and the differential pressure between the membranes of the hollow fiber membrane module 10 will increase in the future.

[0115] In this case, for the multiple backwashing processes, since the pressure on at least one of the primary side and the secondary side of the hollow fiber membrane module 10 is measured at intervals of 3 seconds or less, the arrival point of the pressure that instantaneously increases immediately after the start of the backwashing process can be detected for either the primary side or the secondary side. That is, even if the impurity is such that it peels off from the hollow fiber membrane surface by the force with which the treated water is pushed from the secondary side to the primary side in the backwashing process, the pressure before the decrease due to the peeling off of the impurity can be appropriately detected. As a result, by using the difference in the difference between the pressure on the secondary side and the pressure on the primary side at the detection time point, the change in the amount of impurities attached to the hollow fiber membrane 11 can be appropriately grasped. Therefore, when the prediction unit 71 grasps that the amount of impurities attached to the hollow fiber membrane 11 is increasing, it can appropriately predict that the permeation resistance of the hollow fiber membrane 11 increases and the intermembrane differential pressure of the hollow fiber membrane module 10 rises.

[0116] When the prediction unit 71 predicts an increase in the future intermembrane differential pressure of the hollow fiber membrane module 10, the notification unit 72 notifies the result of the prediction by the prediction unit 71.

[0117] Specifically, the notification unit 72 uses a communication device (not shown) provided in the water treatment apparatus 1 to send an e-mail containing a message indicating that an increase in the future intermembrane differential pressure of the hollow fiber membrane module 10 has been predicted to an information processing apparatus such as a personal computer, a tablet terminal, and a smartphone owned by the administrator of the water treatment apparatus 1. The result of the prediction by the prediction unit 71 is not limited to the above message and may include the logging data (FIG. 3) used by the prediction unit 71 for the prediction.

[0118] Further, the water treatment apparatus 1 may be provided with an audio output device such as a speaker, and the notification unit 72 may output, to the audio output device, an audio indicating that an increase in the transmembrane differential pressure of the hollow fiber membrane module 10 is predicted in the future. Further, the water treatment apparatus 1 may be provided with a display device such as a liquid crystal display, and the notification unit 72 may display the above message and the logging data (FIG. 3) used by the prediction unit 71 for prediction on the display device. Alternatively, the notification unit 72 may combine two or more of these communication devices, audio output devices, and display devices to notify the two or more devices of the result of the prediction by the prediction unit 71.

[0119] Next, in the air venting step (pressure relief step), the air valve 42 and the drain valve 54 are closed, and the pressure relief valve 58 is opened. Thereby, the air accumulated on the secondary side of the hollow fiber membrane module 10 is discharged through the pressure relief pipe 57.

[0120] Next, in the second water filling step, as in the first water filling step, the raw water pump 22 operates, and the raw water valve 23 and the air venting valve 56 are opened respectively.

[0121] Next, in the air diffuser bubbling step, the raw water pump 22 is switched from on to off, the raw water valve 23 is closed, and the first air valve 32 is opened. The air venting valve 56 remains open. Thereby, air is supplied into the housing 12 from the air supply port 12C, and the air is dispersed toward the hollow fiber membrane bundle by the air diffuser 15. Thereby, the hollow fiber membrane bundle sways due to the bubbles, and the impurities attached to the membrane surface are peeled off.

[0122] Next, in the third water filling step, as in the first and second water filling steps, the raw water pump 22 operates, and the raw water valve 23 and the air venting valve 56 are opened respectively. Thereby, the raw water corresponding to the amount drained in the air diffuser bubbling step is replenished into the housing 12.

[0123] Next, in the aqueduct bubbling step, the raw water pump 22 is switched from on to off, the raw water valve 23 is closed, and the second air valve 33 is opened. As a result, the pressurized air from the compressor is supplied into the aqueduct 14 from the air inlet 14B, and is supplied to the raw water space S1 through the hole 14C. Thereby, the hollow fiber membrane bundle is subjected to bubbling cleaning.

[0124] Next, in the drainage step, the air vent valve 56 is closed and the drain valve 54 is opened. Note that the second air valve 33 remains open. As a result, the raw water in the raw water space S1 is pushed by the air and discharged outside the housing 12 from the drain port 12D.

[0125] Finally, in the pressure relief step, the drain valve 54 remains open and the second air valve 33 is closed. Thereby, the air in the housing 12 (raw water space S1) is vented. After the hollow fiber membrane module 10 is physically cleaned by the above process, it returns to the first water filling step and the filtration operation is restarted.

[0126] Note that the timing at which the prediction unit 71 predicts the increase in the transmembrane differential pressure of the hollow fiber membrane module 10 is not particularly limited. For example, it may be every time the operation cycle of FIG. 2 is performed, or every time the operation cycle of FIG. 2 is repeated a plurality of times (for example, 10 times), or once a day, once a week, or once a month. This frequency may be appropriately determined according to the type of raw water (for example, river water, wastewater, or sewage) and the season.

[0127] Also, in the backwashing step, instead of the air pressurized to a predetermined pressure, the treated water on the secondary side may be pressurized by the permeate pressurized to a predetermined pressure. Note that a chemical may be injected into the permeate.

[0128] As described above, in the water treatment apparatus 1 according to the present embodiment, in the backwashing step of the hollow fiber membrane module 10, the pressurized air pushes the treated water on the secondary side to the primary side. As a result, not only can the treated water be permeated at locations on the hollow fiber membrane 11 where impurities are not attached, but it can also be made to collide with the locations where impurities are attached. Consequently, the pressure applied to the treated water can be varied according to the amount of attached impurities. Therefore, it is possible to measure the pressure on at least one of the primary side and the secondary side of the hollow fiber membrane module 10 according to the amount of attached impurities on the hollow fiber membrane 11.

[0129] Moreover, in each of a plurality of backwashing steps, the pressure on at least one of the primary side and the secondary side of the hollow fiber membrane module 10 is measured at intervals of 3 seconds or less, which is shorter than the normal measurement interval of the transmembrane differential pressure in the filtration step. For this reason, it is possible to grasp the detailed temporal change of the pressure on at least one of the sides in each backwashing step that ends within several minutes.

[0130] Therefore, from the differences between the detailed temporal changes in a plurality of backwashing steps, it is possible to grasp the change in the amount of attached impurities on the hollow fiber membrane 11 according to the change in the pressure on at least one of the sides. For this reason, when it is grasped that the amount of attached impurities on the hollow fiber membrane 11 has increased, it is possible to predict that the transmembrane differential pressure will increase in the future, and the prediction result can be notified.

[0131] Note that the timing at which the notification unit 72 notifies the prediction result by the prediction unit 71 is not particularly limited. The notification unit 72 may notify the prediction result each time the prediction unit 71 predicts a future increase in the transmembrane differential pressure, or may collectively notify the prediction results for a predetermined number of times each time the prediction unit 71 predicts a future increase in the transmembrane differential pressure a predetermined number of times.

[0132] (Modified Embodiment) Although the embodiments of the transmembrane differential pressure prediction method and the water treatment apparatus according to the present invention have been described above, the present invention is not limited thereto, and for example, the following modified embodiments can be adopted.

[0133] (1) In the above embodiment, the measurement unit 60 measures the pressures on the primary side and the secondary side of the hollow fiber membrane module 10 in each of a plurality of backwashing steps, and based on the differences in the measurement results between the plurality of backwashing steps, the prediction unit 71 predicts the future increase in the transmembrane differential pressure of the hollow fiber membrane module 10. However, the present invention is not limited to this. The measurement unit 60 may measure the pressure on the primary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less in the same manner as the backwashing step in the above embodiment in each of a plurality of first water filling steps. Alternatively, the measurement unit 60 may measure the pressure on the primary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less in the same manner as the backwashing step in the above embodiment only in each of a plurality of first water filling steps. Then, the prediction unit 71 may predict the future increase in the transmembrane differential pressure of the hollow fiber membrane module 10 based on the differences in the measurement results between the plurality of first water filling steps.

[0134] Specifically, in the first water filling step, the primary side pressure sensor 61 measures the pressure on the primary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less. As a result, logging data (FIG. 7) showing the time change of the pressure on the primary side of the hollow fiber membrane module 10 during the first water filling step is obtained. In the graph of FIG. 7, the horizontal axis represents time, and the vertical axis represents the pressure on the primary side of the hollow fiber membrane module 10.

[0135] As shown in FIG. 7, when the first water filling process is started (time point t70 in FIG. 7) and raw water flows into the inside of the hollow fiber membrane module 10, the pressure on the primary side gradually increases due to the head pressure inside the hollow fiber membrane module 10. Thereafter, when the inside of the hollow fiber membrane module 10 approaches a full water state (time point t71 in FIG. 7), raw water flows into the air vent pipe 55. At this time, since the diameter of the air vent pipe 55 is smaller than the diameter of the housing 12, a pipeline resistance is generated, and the pressure on the primary side rapidly increases. Therefore, the time t70 to t71 from the start of the first water filling process to reaching the inflection point of the change in the pressure on the primary side, indicated by the double-headed arrow in FIG. 7, becomes shorter as the accumulation amount of impurities inside the hollow fiber membrane module 10 is larger and the effective volume inside the hollow fiber membrane module 10 is smaller.

[0136] Also, it is presumed that the larger the accumulation amount of impurities inside the hollow fiber membrane module 10 and the smaller the effective volume inside the hollow fiber membrane module 10, the larger the amount of impurities attached to the hollow fiber membrane 11, that is, it is presumed that the intermembrane differential pressure of the hollow fiber membrane module 10 will increase in the future.

[0137] For this reason, the prediction unit 71 may refer to the logging data (FIG. 7) stored in the control unit 70 and predict the future increase in the intermembrane differential pressure of the hollow fiber membrane module 10 based on the differences among multiple first water filling processes in the time (t70 to t71 in FIG. 7) from the start of the first water filling process to reaching the inflection point of the change in the pressure on the primary side.

[0138] Specifically, it is assumed that the time (t70 to t71 in FIG. 7) from the start of the first water filling process to reaching the inflection point of the change in the pressure on the primary side shows a decreasing trend among multiple first water filling processes. In this case, since the accumulation amount of impurities inside the hollow fiber membrane module 10 is increasing and the effective volume inside the hollow fiber membrane module 10 is decreasing, the prediction unit 71 may predict that the intermembrane differential pressure of the hollow fiber membrane module 10 will increase in the future.

[0139] As described above, in this modified embodiment, in the first water filling step, the pressure on the primary side of the hollow fiber membrane module 10 is measured when raw water fills the inside of the hollow fiber membrane module 10. Therefore, in this modified embodiment, the pressure on the primary side of the hollow fiber membrane module 10 can be measured according to the accumulation amount of impurities inside the hollow fiber membrane module 10.

[0140] Moreover, in this modified embodiment, in each of the plurality of first water filling steps, the pressure on the primary side of the hollow fiber membrane module 10 is measured at intervals of 3 seconds or less, which is shorter than the normal measurement interval of the differential pressure between membranes in the filtration step. Therefore, the detailed temporal change of the pressure on the primary side of the hollow fiber membrane module 10 in each first water filling step that ends within several minutes can be grasped.

[0141] Therefore, from the differences between the plurality of first water filling steps of this detailed temporal change, the change in the accumulation amount of impurities inside the hollow fiber membrane module 10 corresponding to the change in the pressure on the primary side of the hollow fiber membrane module 10 can be grasped.

[0142] Specifically, due to the difference in time t70~t71 (Fig. 7) from the start time point t70 (Fig. 7) of the first water filling step to the time point t71 (Fig. 7) when reaching the inflection point of the change in the pressure on the primary side between the plurality of first water filling steps, the change in the accumulation amount of impurities and the effective volume inside the hollow fiber membrane module 10 can be grasped. Therefore, when it is grasped that the accumulation amount of impurities inside the hollow fiber membrane module 10 is increasing and the effective volume inside the hollow fiber membrane module 10 is decreasing, it is possible to appropriately predict that the amount of impurities attached to the hollow fiber membrane 11 is increasing, that is, the differential pressure between membranes will increase in the future, and the prediction result can be notified.

[0143] (2) In the above-described modified embodiment, an example has been described in which the measurement unit 60 measures the pressure on the primary side of the hollow fiber membrane module 10 in each of a plurality of first water filling steps, and based on the differences in the measurement results between the plurality of first water filling steps, the prediction unit 71 predicts the future increase in the intermembrane differential pressure of the hollow fiber membrane module 10. Similarly, the measurement unit 60 may measure the pressure on the primary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less in each of a plurality of drainage steps. Alternatively, the measurement unit 60 may measure the pressure on the primary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less only in each of a plurality of drainage steps. Then, based on the differences in the measurement results between the plurality of drainage steps, the prediction unit 71 may predict the future increase in the intermembrane differential pressure of the hollow fiber membrane module 10.

[0144] Specifically, in the drainage step, the primary side pressure sensor 61 measures the pressure on the primary side of the hollow fiber membrane module 10 at intervals of 3 seconds or less. Thereby, logging data (FIG. 8) showing the time change of the pressure on the primary side of the hollow fiber membrane module 10 during the drainage step is obtained. In the graph of FIG. 8, the horizontal axis represents time, and the vertical axis represents the pressure on the primary side of the hollow fiber membrane module 10.

[0145] As shown in FIG. 8, when the drainage step is started (time point t80 in FIG. 8), the drain water inside the hollow fiber membrane module 10 is discharged through the drain pipe 53 (FIG. 1). Thereafter, when the discharge of the drain water inside the hollow fiber membrane module 10 is completed (time point t81 in FIG. 8), the pressure on the primary side stabilizes at a predetermined drainage end pressure near 0 KPa indicating the end of the discharge of the drain water. Therefore, the time t80 to t81 from the start of the drainage step until the pressure on the primary side becomes constant, indicated by the double arrow in FIG. 8, becomes shorter as the amount of impurities accumulated inside the hollow fiber membrane module 10 is larger and the effective volume inside the hollow fiber membrane module 10 is smaller.

[0146] Further, the greater the accumulation amount of impurities inside the hollow fiber membrane module 10 and the smaller the effective volume inside the hollow fiber membrane module 10, the greater the amount of impurities attached to the hollow fiber membrane 11 is presumed to be. That is, it is presumed that the intermembrane differential pressure of the hollow fiber membrane module 10 will increase in the future.

[0147] Therefore, the prediction unit 71 may refer to the logging data (FIG. 8) stored in the control unit 70 and predict the future increase in the intermembrane differential pressure of the hollow fiber membrane module 10 based on the differences between multiple drainage processes in the time (t80 to t81 in FIG. 8) from the start of the drainage process until the pressure on the primary side becomes constant.

[0148] Specifically, it is assumed that the time (t80 to t81 in FIG. 8) from the start of the drainage process until the pressure on the primary side becomes constant shows a decreasing trend among multiple drainage processes. In this case, since the accumulation amount of impurities inside the hollow fiber membrane module 10 is increasing and the effective volume inside the hollow fiber membrane module 10 is decreasing, the prediction unit 71 may predict that the intermembrane differential pressure of the hollow fiber membrane module 10 will increase in the future.

[0149] As described above, in this modified embodiment, in the drainage process, the pressure on the primary side of the hollow fiber membrane module 10 when the drain water inside the hollow fiber membrane module 10 is discharged is measured. Therefore, in this modified embodiment, the pressure on the primary side of the hollow fiber membrane module 10 corresponding to the accumulation amount of impurities inside the hollow fiber membrane module 10 can be measured.

[0150] Moreover, in this modified embodiment, in each of the multiple drainage processes, the pressure on the primary side of the hollow fiber membrane module 10 is measured at intervals of 3 seconds or less, which is shorter than the normal measurement interval of the intermembrane differential pressure in the filtration process. Therefore, the detailed temporal change of the pressure on the primary side of the hollow fiber membrane module 10 in each drainage process that ends within several minutes can be grasped.

[0151] Therefore, according to this modified embodiment, from the differences between multiple drainage processes of this detailed time progression, it is possible to grasp the change in the accumulation amount of impurities inside the hollow fiber membrane module 10 in response to the change in the pressure on the primary side of the hollow fiber membrane module 10.

[0152] Specifically, from the difference in the time t80 - t81 (FIG. 8) from the start time point t80 (FIG. 8) of the drainage process to the time point t81 (FIG. 8) when the pressure on the primary side becomes constant during multiple drainage processes, it is possible to grasp the change in the accumulation amount of impurities and the effective volume inside the hollow fiber membrane module 10. For this reason, when it is grasped that the accumulation amount of impurities inside the hollow fiber membrane module 10 is increasing and the effective volume inside the hollow fiber membrane module 10 is decreasing, it is possible to appropriately predict that the amount of impurities attached to the hollow fiber membrane 11 is increasing, that is, the situation where the intermembrane differential pressure will increase in the future, and the prediction result can be notified.

[0153] The embodiments and their modified embodiments disclosed this time should be understood as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all changes within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0154] 1: Water treatment device 10: Hollow fiber membrane module 11: Hollow fiber membrane 60: Measurement unit 71: Prediction unit 72: Notification unit

Claims

1. A water treatment device that filters raw water using a hollow fiber membrane module, a measuring unit that measures the pressure on at least one of the primary side and the secondary side at intervals of 3 seconds or less in each of the multiple backwashing processes when a backwashing process is performed multiple times in which treated water on the secondary side of the hollow fiber membrane module is pushed to the primary side of the hollow fiber membrane module by a pressurized medium; a prediction unit that predicts a future increase in transmembrane pressure difference of the hollow fiber membrane module based on a difference in the measurement results of the pressure on at least one side between the multiple backwashing processes; a notification unit that notifies a prediction result by the prediction unit; a communication device; Equipped with The notification of the prediction result by the notification unit is and transmitting, using the communication device, an email including a message indicating that a future increase in the transmembrane pressure difference of the hollow fiber membrane module has been predicted, to an information processing device owned by an administrator of the water treatment device. Water treatment equipment.

2. The email further includes logging data indicating the pressure on at least one side used by the prediction unit for prediction. The water treatment device according to claim 1 .

3. Further comprising a control unit that sequentially executes each step constituting the filtration operation cycle, the prediction unit predicts a future increase in the transmembrane pressure difference of the hollow fiber membrane module every time the operation cycle is performed, every time the operation cycle is repeated multiple times, or once per period of one month or less. The water treatment device according to claim 1 .

4. The notification unit notifies the prediction result each time the prediction unit predicts a future increase in the transmembrane pressure difference of the hollow fiber membrane module, or notifies the prediction results for a predetermined number of times each time the prediction unit predicts a future increase in the transmembrane pressure difference of the hollow fiber membrane module a predetermined number of times. The water treatment device according to claim 3 .

5. Further comprising an audio output device, The notification of the prediction result by the notification unit is and further comprising causing the audio output device to output a sound indicating that a future increase in transmembrane pressure difference of the hollow fiber membrane module has been predicted. The water treatment device according to claim 1 .

6. Further comprising a display device, The notification of the prediction result by the notification unit is and further comprising displaying, on the display device, the message or logging data indicating the pressure on at least one side used by the prediction unit for prediction. The water treatment device according to claim 1 or 5.

7. The ratio of the inner diameter of the housing to the inner diameter of the piping connection port provided in the raw water space within the housing of the hollow fiber membrane module is 1.3 or more and 12 or less. The water treatment device according to claim 1 .

8. In the backwashing process, the medium is pressurized to a pressure of 30 kPa or more and 500 kPa or less. The water treatment device according to claim 1 .

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