CN113966249A - Filtering membrane cleaning device, filtering membrane cleaning method and water treatment system - Google Patents

Abstract

The filtration membrane cleaning apparatus of the present invention comprises: an ozone water generation tank (12) for dissolving ozone gas in water to generate ozone water and storing the generated ozone water and a by-product ozone exhaust gas; a reverse cleaning mechanism for reverse cleaning the filtering membrane (51) by using the stored ozone water for the filtering unit (5) for filtering the raw water; a membrane surface cleaning mechanism for discharging bubbles containing ozone in the biological reaction tank (4) and cleaning the membrane surface of the filtration membrane (51); a control unit (30) for controlling the operations of the reverse cleaning mechanism and the membrane surface cleaning mechanism so that the membrane surface is cleaned by the membrane surface cleaning mechanism before the reverse cleaning by the reverse cleaning mechanism; and an exhaust ozone gas diluting unit that dilutes the stored exhaust ozone gas and supplies the diluted exhaust ozone gas to the membrane surface cleaning mechanism as gas discharged as bubbles during membrane surface cleaning.

Description

Filtering membrane cleaning device, filtering membrane cleaning method and water treatment system

Technical Field

The application relates to a filtering membrane cleaning device, a filtering membrane cleaning method and a water treatment system.

Background

As a water treatment method for removing suspended substances and bacteria from waste water or the like such as tap water, dirty water, and industrial waste water containing organic substances, there is a method of membrane separation by a filtration membrane. Since the filtration membrane has pores with a smaller diameter than suspended matter and bacteria, suspended matter and bacteria can be stably removed from raw water such as wastewater, but when the treatment is continued, the pores may be clogged by the attached suspended matter. When the fine pores are clogged, the pressure difference between the membranes increases and the amount of filtered water decreases, thereby reducing the treatment capacity, and therefore, it is necessary to periodically perform cleaning called reverse cleaning in which a cleaning agent is caused to flow in a direction opposite to the filtration direction to remove suspended matter attached to the inside or the surface of the filtration membrane.

Ozone having a high oxidizing power and easy post-treatment is considered to be suitable as the cleaning agent, but ozone water obtained by dissolving ozone in water is used to prevent the pore structure from being changed by drying the film. At this time, in order to obtain a sufficient cleaning effect, it is necessary to generate ozone water in which ozone is dissolved until the solubility approaches saturation, but undissolved ozone gas as a by-product is wastefully discharged as an exhaust ozone gas.

Therefore, a technique has been proposed in which an exhaust ozone gas is used for volume reduction of excess sludge in a reaction tank or for surface cleaning of a primary side of a filtration membrane (membrane surface cleaning), thereby achieving effective use of ozone (for example, see patent document 1 or patent document 2).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2001-70761 (paragraphs 0013 to 0014, 0017, FIG. 1)

Patent document 2: japanese patent No. 6271109 (paragraphs 0021 to 0034, FIGS. 3 to 6)

Disclosure of Invention

Technical problem to be solved by the invention

Indeed, the exhaust ozone gas has an oxidizing effect and is believed to contribute to the reduction of the volume of excess sludge. However, when the exhaust ozone gas is actually fed into the reaction tank, it is found that the pressure difference between membranes is increased or the time required for the back washing is increased although the volume of the excess sludge is reduced. That is, the introduction of the exhaust ozone gas into the reaction vessel does not necessarily improve the cleaning efficiency of the filtration membrane.

The present application discloses a technique for solving the above-mentioned problems, and an object thereof is to obtain a filtration membrane cleaning apparatus, a filtration membrane cleaning method, and a water treatment system capable of effectively utilizing ozone and effectively cleaning a filtration membrane.

Means for solving the problems

The filtering membrane cleaning apparatus disclosed in the present application is characterized by comprising: a storage unit that dissolves ozone gas in water to generate ozone water and stores the generated ozone water and a by-product ozone-containing waste gas; a reverse cleaning mechanism that performs reverse cleaning of a filter unit provided in the biological reaction tank for filtering raw water, the reverse cleaning causing ozone water taken out of the storage unit to flow from a secondary side to a primary side of the filter membrane; a membrane surface cleaning mechanism that performs membrane surface cleaning that discharges bubbles containing ozone in the biological reaction tank and causes the discharged bubbles to flow along a surface on a primary side of the filtration membrane; a control unit that controls operations of the reverse cleaning mechanism and the membrane surface cleaning mechanism so that the membrane surface is cleaned by the membrane surface cleaning mechanism before the reverse cleaning by the reverse cleaning mechanism; and an exhaust ozone gas diluting section that dilutes an exhaust ozone gas and supplies the exhaust ozone gas to the membrane surface cleaning mechanism, wherein the exhaust ozone gas is taken out from the storage section as a gas discharged as the bubbles.

The method for cleaning a filtration membrane disclosed in the present application is characterized by comprising: a storage step of dissolving ozone gas in water to generate ozone water, and storing the generated ozone water and an exhaust ozone gas as a by-product; a membrane surface cleaning step of causing bubbles containing ozone gas to flow along a surface of a primary side of a filtration membrane to a filtration unit for filtering raw water; and a reverse cleaning step of taking out the ozone water stored in the storing step and allowing the taken-out ozone water to flow from the secondary side to the primary side of the filtration membrane, wherein the membrane surface cleaning step dilutes the ozone exhaust gas stored in the storing step and flows the diluted ozone exhaust gas as the bubbles.

Effects of the invention

According to the filtration membrane cleaning apparatus and the filtration membrane cleaning method disclosed in the present application, since the exhaust ozone gas is diluted to generate bubbles for membrane surface cleaning, the filtration membrane can be cleaned efficiently.

Drawings

Fig. 1 is a schematic diagram showing the configurations of a filtration membrane cleaning apparatus according to embodiment 1 and a water treatment system having the filtration membrane cleaning apparatus.

Fig. 2 is a flowchart showing a filtration membrane cleaning method according to embodiment 1.

Fig. 3A to 3B are schematic cross-sectional views each showing a state of classifying a state in which the filtration membrane is clogged into three types.

Fig. 4 is a graph showing a relationship between a distance from a discharge portion when bubbles containing ozone gas are discharged in water and an ozone concentration in the bubbles.

Fig. 5 is a schematic diagram showing the configurations of a filtration membrane cleaning apparatus according to embodiment 2 and a water treatment system having the filtration membrane cleaning apparatus.

Fig. 6 is a schematic diagram showing the structure of a filtration membrane cleaning apparatus according to embodiment 3.

Fig. 7 is a flowchart showing a filtration membrane cleaning method according to embodiment 3.

Fig. 8 is a schematic diagram showing the configurations of a filtration membrane cleaning apparatus according to embodiment 4 and a water treatment system having the filtration membrane cleaning apparatus.

Fig. 9 is a flowchart showing a filtration membrane cleaning method according to embodiment 4.

Fig. 10 is a schematic diagram showing a piping configuration when switching of the process is controlled for each of a plurality of filters in the water treatment system according to embodiment 5.

Fig. 11 is a block diagram showing a hardware configuration of a control unit of the filtration membrane cleaning apparatus according to each embodiment.

Detailed Description

Embodiment 1.

Fig. 1 to 3 are drawings for explaining a filtration membrane cleaning apparatus, a water treatment system having the filtration membrane cleaning apparatus, and a filtration membrane cleaning method according to embodiment 1, fig. 1 is a schematic diagram showing the configurations of the filtration membrane cleaning apparatus and the water treatment system having the filtration membrane cleaning apparatus, and fig. 2 is a flowchart showing a filtration membrane cleaning method which is a part related to the cleaning of a filtration membrane in the operation of the water treatment system having the filtration membrane cleaning apparatus. Fig. 3A to 3B are schematic cross-sectional views of the filtration membrane portions showing the respective states of classification when the clogging states of the filtration membranes are classified into 3 types. Further, fig. 4 shows a graph of the relationship between the distance from the release portion and the ozone concentration in the bubbles when releasing the exhaust ozone gas and the bubbles diluting the exhaust ozone gas in the water containing sludge. Fig. 1 shows the open/close state of the valve in the step of cleaning the membrane surface.

In the water treatment system 1, as shown in fig. 1, a filter unit 5 is installed in a biological reaction tank 4, and the biological reaction tank 4 stores raw water such as tap water, sewage, and industrial wastewater containing organic substances to be treated. In the filtration unit 5, a filtration membrane 51 (see fig. 3) is used, and the filtration membrane 51 has pores having a smaller pore size than the suspended matter, whereby the filtration membrane 51 is used for performing a cleaning process by separating the suspended matter from the mixed water Wr of the biological reaction tank stored in the biological reaction tank 4. The filtration membrane 51 is an organic hollow fiber membrane made of a material having ozone resistance, such as polyvinylidene fluoride (PVDF) or Polytetrafluoroethylene (PTFE). The side of the filtration membrane 51 that contacts the mixed water Wr of the bioreactor tank, that is, the upstream side in the filtration step is referred to as the primary side, and the side that contacts the water (filtered water) after the washing treatment, that is, the downstream side in the filtration step is referred to as the secondary side.

A raw water pipe 71 for supplying raw water to the primary side of the filtration is connected to the biological reaction tank 4, and a filter pipe 72 for taking out filtered water after the cleaning treatment is connected to a secondary side portion (e.g., a frame not shown) of the filter unit 5. The filter pump 44 for sucking filtered water from the filter unit 5 is disposed at the tip of the filter pipe 72. A three-way valve 45 is provided at the tip of the filtration pump 44, and the three-way valve 45 switches between a filtered water feed pipe 73 for feeding the sucked filtered water to a filtered water tank, not shown, and a filtered water feed pipe 24 for feeding the sucked filtered water to the filtration membrane treatment apparatus 10.

Further, a gas diffusion device 41 is provided in the lower portion of the filtration unit 5 in the biological reaction tank 4, the gas diffusion device 41 serving to form an upward flow of the biological reaction tank mixed water Wr that flows upward along the membrane surface of the primary side of the filtration membrane 5 by an air lift action. The gas diffusion device 41 is connected to a blower 42 as an inflation air supply source via an inflation pipe 43.

The filtration membrane cleaning apparatus 10 is an apparatus for cleaning the filtration membrane 51 by causing ozone water as cleaning water to flow to the filtration membrane 51 in the filtration unit 5 in a direction opposite to the filtration. Basically, the ozone water generating apparatus 12 includes an ozone gas generating apparatus 11 and an ozone water generating apparatus 12, and the ozone water generating apparatus 12 generates ozone water using ozone gas supplied from the ozone gas generating apparatus 11.

The ozone gas generator 11 is composed of a raw material gas supply part, not shown, and an ozone gas generation part, not shown, which generates ozone gas using oxygen gas supplied from the raw material gas supply part as a raw material. As the raw material gas supply unit, for example, an oxygen gas generator using a liquid oxygen cylinder, VPSA (Vacuum Pressure Swing Adsorption) or the like is used, but the supply of oxygen gas is not particularly limited as long as it is possible. As the ozone gas generating portion, for example, a discharge type ozone generating device can be used.

The shape of the ozone water generation tank 12 is not limited, and is formed, for example, in a vertically long tank shape, and the filtered water supplied from the filtered water supply pipe 24 is stored inside by the three-way valve 45. A liquid phase region Pw occupied by ozone water in which ozone is dissolved is formed in the lower part and the middle part of the ozone water generation tank 12, and a gas phase region occupied by an exhaust ozone gas derived from ozone water generation is formed in the upper part.

The intermediate portion in the vertical direction of the ozone water generation tank 12 and the tank bottom portion in which the liquid phase region Pw is formed are provided with connection ports to a circulation pipe 22 for circulating water (ozone water) in the liquid phase region Pw. The circulation pipe 22 is provided with a circulation pump 15 for sucking water in the tank from a connection port provided at the bottom of the tank and returning the water from a connection port provided at the middle portion. Further, a gas suction device 14 is provided for generating ozone water by dissolving ozone gas in the water flowing through the circulation pipe 22, and the gas suction device 14 sucks the ozone gas supplied from the ozone gas generation device 11 by, for example, a venturi effect.

In the present embodiment, the inlet and the outlet of the circulation pipe 22 are connected to the liquid phase region Pw portions of the tank bottom and the middle portion of the ozone water generation tank 12, respectively, but not limited thereto. The inlet may be located in any of the liquid phase zones Pw and the outlet may be located at the bottom of the tank or in a part of the gas phase zone Pg. The ozone water may be flowed into the circulation pipe 22 and returned to the ozone water generation tank 12.

Further, the structure for generating ozone water is not limited to the use of the gas suction device 14. For example, as disclosed in patent document 2, a gas diffusion device for blowing ozone gas may be provided in the liquid phase region Pw, and the effects of the present invention can be obtained as long as the ozone gas is brought into contact with water to generate ozone water, thereby generating an exhaust ozone gas.

On the other hand, in the present embodiment, the ozone in the ozone gas generation device 11 is sucked and dissolved by the negative pressure generated by the fluid flow in the gas suction device 14, and therefore, it is not necessary to supply the pressurized ozone gas from the ozone gas generation device 11. However, when bubbling ozone gas in the ozone water generation tank 12, an ozone generation device having a structure for generating a required pressure is required.

Another three-way valve 16 connected to the ozone water supply pipe 25 is provided between the circulation pump 15 and the gas suction device 14, and the three-way valve 16 is configured to be switchable between circulation for generating ozone water and supply of ozone water to the filter unit 5. In fig. 1, the three-way valve 16 is oriented so that the filter pump 15 communicates with the gas suction device 14, and the water (ozone water) in the liquid phase region Pw is set as a path circulating through the ozone water generation tank 12 and the circulation pipe 22. When the three-way valve 16 is switched to communicate the circulation pump 15 with the ozone water supply pipe 25, ozone water can be supplied to the secondary side of the filter unit 5 for reverse cleaning.

In addition to the above-described structure, the water treatment system 1 and the filtration membrane cleaning apparatus 10 include a control section, not shown, for controlling the operation, and they are basic structures of the filtration membrane cleaning apparatus 10 and the water treatment system 1 having the filtration membrane cleaning apparatus 10. In addition to this basic configuration, the filtration membrane cleaning apparatus 10 according to each embodiment of the present application is connected to an exhaust ozone gas pipe 23, and the exhaust ozone gas pipe 23 is used to introduce the exhaust ozone gas generated in the ozone water generation tank 12 into the biological reaction tank 4. Specifically, the exhaust ozone gas pipe 23 is connected to a connection port provided at the top of the ozone water generation tank 12 where the gas phase region Pg is formed. Further, an on-off valve 17 for controlling opening and closing and a buffer tank 13 are provided in the exhaust ozone gas pipe 23. The capacity of the buffer tank 13 or the capacity of the ozone water generation tank 12 is appropriately designed according to the amount of the exhaust ozone gas required for membrane surface cleaning or the amount of the ozone water required for reverse cleaning, which will be described later.

In the filtration membrane cleaning apparatus 1 according to embodiment 1, the distal end opening 23x of the exhaust ozone gas pipe 23 is positioned in the portion directly below the filter unit 5 in the biological reaction tank 4, and air from the blower 42 is mixed in the middle. Specifically, a branching portion that communicates with the branching portion 46 of the aeration pipe 43 is provided between the on-off valve 17 and the distal end opening portion 23x of the exhaust ozone gas pipe 23. The configuration is such that air from the blower 42 can be added to the exhaust ozone gas by opening the on-off valve 18 provided at the branch portion.

Next, referring to the flowchart of fig. 2, as an operation, an operation based on the basic configuration will be described first.

In the step of filtering the raw water (step S10), as shown in fig. 1, the raw water is introduced into the biological reaction tank 4 from the raw water pipe 71, and the biological reaction tank mixed water Wr in the biological reaction tank 4 is subjected to solid-liquid separation into suspended matter and filtered water in the filter unit 5 by suction of the filter pump 44. In the schematic diagrams of the respective embodiments including fig. 1, unless otherwise specified, the open and closed states of the valves in the membrane surface cleaning process by the exhaust ozone gas are shown.

The mixed water Wr of the biological reaction tank flowing into the primary side is treated with organic sludge containing a microorganism complex called activated sludge, and the purified water is separated from the activated sludge and suspended solids by the filtration membrane 51 and flows to the secondary side as filtered water. The filtered water flowing to the secondary side is sent to the filtered water tank via the filtered water pipe 72, the filter pump 44, the three-way valve 45, and the filtered water delivery pipe 73. In the step of treating raw water, the three-way valve 16 is in the circulation state, but the on-off valves 17 and 18 are in the closed state unlike fig. 1, and therefore the flow between the filtration unit 5 and the filtration membrane cleaning apparatus 10 can be cut off.

When the conditions for ending the process of treating the raw water are satisfied ("yes" in step S20), the supply of the raw water and the operation of the filter pump 44 are stopped, and the filtration process is ended. It is originally preferable that the conditions for terminating the filtration step be controlled by, for example, a pressure difference between membranes which indicates the degree of clogging of the filtration membrane 51. However, in actual use, the properties of the raw water may be set by setting appropriate indexes such as a filtration time or a flow rate of the filtered water discharged from the filter pump 44 as long as the properties of the raw water do not change extremely.

When the filtration step is completed, the process proceeds to a step of cleaning the filtration membrane 51 with ozone. In a method for cleaning a filtration membrane using ozone water, an ozone water generation step (steps S30 to S90) for generating ozone water and an ozone water reverse cleaning step (steps S100 to S120) using the generated ozone water are performed. The method for cleaning a filtration membrane according to the present invention is characterized by performing a membrane surface cleaning step using an ozone-containing gas after dilution in the ozone water generation step (steps S50 to S70). The respective steps will be explained below.

In the ozone water generation step, the circulation pump 15 is started to circulate the water in the liquid region Pw of the ozone water generation tank 12 through the circulation pipe 22, and the ozone gas generated in the ozone gas generation device 11 is dissolved in the gas suction device 14, thereby starting the generation of ozone water (step S30). At this time, the ozone water in which ozone is dissolved is returned to the ozone water generation tank 12 while containing bubbles of undissolved exhaust ozone gas. At this time, the dissolved ozone concentration Co in the liquid phase region Pw in the ozone water generation tank 12 increases, and the tank internal pressure Pt increases by flowing the exhaust ozone gas.

As a first stage in this step, it is judged whether or not the amount of the ozone waste gas derived from the ozone water generation can be secured as much as the amount necessary for the membrane surface cleaning (step S40). Strictly speaking, after the volume of the gas phase region Pg is grasped, it is necessary to confirm the tank internal pressure Pt indicating the amount of the predetermined amount of the exhaust ozone gas and the ozone gas concentration in the exhaust ozone gas, and either one of them may be confirmed, or the supply time of the ozone gas or other indicators may be used. Here, the end condition is that the supply time of the ozone gas has elapsed for a certain time or more, and the end condition is that the ozone gas is continuously supplied until the elapsed time reaches a predetermined time (no in step S40).

When the supply time reaches the predetermined time (yes in step S40), it is determined that the termination condition has been satisfied, the circulation pump 15 is stopped, the supply of the exhaust ozone gas from the gas suction device 14 is stopped, and the process proceeds to the membrane surface cleaning step using the exhaust ozone gas (steps S50 to S70). In the membrane surface cleaning step, the on-off valve 17 is opened to introduce the ozone-containing gas stored in the gas phase region Pg of the ozone-water generating tank 12 (and the buffer tank 13) into the ozone-containing gas pipe 23. The on-off valve 18 is opened to introduce air from the blower 42 into the exhaust ozone gas pipe 23, dilute the exhaust ozone gas, and discharge the diluted exhaust ozone gas from the front end opening 23x (step S50). This process is continued until the second predetermined time elapses (no in step S60).

At this time, an unillustrated on-off valve provided between the aeration pipe 43 and the gas diffusion device 41 is closed, and only the diluted exhaust ozone gas is discharged from the front end opening portion 23x directly below the filter unit 5. The diluted ozone gas discharged directly below the filter unit 5 flows as bubbles along the primary side surface 51f1 (see fig. 3) which is the primary side surface of the filter membrane 51 of the filter unit 5.

The bubbles of the diluted exhaust ozone gas flowing along the primary side surface 51f1 of the filtration membrane 51 peel off/remove suspended matter adhering to the membrane surface of the filtration membrane 51 by the physical action of the shearing force and the chemical action of the ozone gas as the oxidizing gas, thereby cleaning the membrane surface of the filtration membrane 51. This cleaning has an effect of weakening the adhesion to the filter membrane 51 even for the adhered matter that cannot be peeled off/removed. Thus, the diluted exhaust ozone gas supplied to the primary side functions as an aeration gas for membrane surface cleaning. Thereby, the exhaust ozone gas is consumed in the filtering unit 5, and the contamination of the filtering membrane 51 is reduced.

Here, the necessity of diluting the exhaust ozone gas flowing to the film surface is explained. As shown in fig. 3A to 3C, clogging (fouling) of the filter membrane 51 is mainly classified into three types depending on the state of the organic matter 90 deposited. The first type: as shown in fig. 3A, a membrane clogging substance 90a (activated sludge or suspended particles) such as activated sludge sufficiently larger than the diameter (membrane pore diameter) of the pores 51p of the filtration membrane 51 is deposited on the membrane surface (primary side surface 51f1) to form a cake layer. The second type: as shown in fig. 3B, the membrane clogging substance 90e having a size substantially equal to the pore diameter of the membrane enters the inlet (primary side) of the pore 51p or the inside thereof, and causes membrane fouling to clog the pore 51 p. In the third category: as shown in fig. 3C, the membrane-clogging substance 90f sufficiently smaller than the membrane pore diameter passes through the pores 51p, but a part of the membrane-clogging substance 90f adsorbs/adheres to the inner wall surfaces of the pores 51p, thereby gradually clogging the pores 51 p.

The first type of membrane fouling generated due to the cake layer attached to the membrane surface is mainly classified as reversible membrane fouling, and the second type of complete clogging, the third type of standard clogging, or the like, membrane fouling generated at the inlet and inside of the fine pores 51p is classified as irreversible membrane fouling. When the membrane is irreversibly contaminated, the membrane cannot be recovered by physical cleaning such as aeration (corresponding to membrane cleaning) or filtration, but the membrane can be recovered only by chemical cleaning. On the other hand, in the case of reversible contaminations of the first type, recovery by physical cleaning is also possible.

When the ozone gas comes into contact with the activated sludge, cell walls of bacteria in the activated sludge are destroyed, and soluble organic substances 90 and the like contained in the bacteria are released into the liquid phase. This is a known technique for remultilization (solubilization) of ozone-activated sludge. When a high-concentration ozone gas is continuously supplied from the lower portion of the membrane, the activated sludge is dissolved, and the organic matter concentration in the liquid phase portion around the filtration membrane 51 increases. Then, soluble components, colloidal components, and the like released from the sludge are easily accumulated on the membrane surface to form a state as shown in fig. 3B or 3C, or a gel layer is easily formed on the membrane surface, the gel layer not being a cake layer formed by activated sludge but forming physically irreversible membrane fouling by the dissolved organic matter 90. That is, when the exhaust ozone gas is constantly fed, irreversible membrane fouling occurs, and the frequency of chemical cleaning with ozone water, sodium hypochlorite, or the like increases, which may increase the running cost.

On the other hand, in embodiment 1 and the following embodiments, a diluted exhaust ozone gas having a low concentration is used for cleaning the film surface, instead of a high-concentration exhaust ozone gas. Therefore, the generation of the membrane-clogging substance 90e or the membrane-clogging substance 90f due to the re-homogenization (solubilization) of the activated sludge is suppressed, and the irreversible membrane fouling is not easily brought into a state in which it is easy to progress, thereby suppressing an increase in the running cost of the chemical cleaning.

Therefore, as the influence of the ozone gas concentration in the bubbles used for the membrane surface cleaning, the chemical cleaning effect and the possibility of occurrence of irreversible membrane fouling (non-evoked property) were evaluated experimentally, and the results are shown in table 1.

[ Table 1]

TABLE 1 concentration of bubble ozone in Membrane surface cleaning and its effect on sludge

As shown in Table 1, if the ozone concentration is maintained at C₂(30g/m³) The above results show that the chemical cleaning effect is sufficiently exhibited (good), and the ozone concentration is maintained at C₁(10g/m³) Less than C₂Within the range of (d), the chemical cleaning effect is insufficient (Δ), and if the ozone concentration is kept less than C1, the chemical cleaning effect is at a level (x) not different from the aeration of air. In addition, if the ozone concentration is maintained at C₃(150g/m³) Hereinafter, irreversible film contamination does not occur (good), but when C is exceeded₃Irreversible membrane fouling will occur, if C is exceeded₄(200g/m³) Clogging due to irreversible membrane fouling becomes significant (x).

That is, it is known that the concentration of ozone in the exhaust ozone gas used for membrane surface cleaning is adjusted to C so as not to cause irreversible membrane fouling₃(150g/m³: standard state) as follows. On the other hand, as shown in fig. 4, the concentration of ozone in the air bubbles released in the bioreactor tank 4 for membrane surface cleaning decreases as the air flows along the membrane surface and moves away from the released portion. Therefore, in order to maintain the chemical cleaning effect of the ozone gas over the entire surface of the membrane surface (to enter the membrane surface cleaning effective region), it is preferable to adjust the concentration at the time of discharge so that the concentration at the farthest position becomes C₂(30g/m³) The above.

Here, the dissolved ozone concentration Co of the ozone water for the back washingPreferably 30mg/L, and the concentration of ozone gas for producing ozone water in this concentration range is 200g/m³. When ozone gas is dissolved in water, the ozone concentration of the derived exhaust ozone gas depends on the dissolved ozone concentration Co of the water to be dissolved, and as the dissolved ozone concentration Co increases, the ozone concentration of the generated exhaust ozone gas also increases. However, although the temperature and the pressure are varied, the concentration of the exhaust ozone gas stored in the gas phase region Pg when the dissolved ozone concentration Co of the ozone water in the liquid phase region Pw reaches a necessary range is actually 100g/m³～200g/m³Within the range of (1).

Therefore, even if the concentration of the exhaust ozone gas is not strictly measured, the concentration can be adjusted to a desired concentration by controlling the dilution ratio. Therefore, the membrane surface cleaning can be efficiently performed by diluting the exhaust ozone gas by 1.4 times or more instead of controlling the concentration. At this time, when the dilution ratio is kept at 3 times or less, 30g/m can be obtained³The above ozone gas concentration also ensures that the chemical cleaning effect can be obtained.

Further, when the membrane surface cleaning is performed, the diluted exhaust ozone gas having a low concentration is supplied instead of the high concentration exhaust ozone gas, there are the following advantages. When the bubbles containing ozone gas are discharged just below the filter unit 5, the bubbles move upward along the membrane surface. During the upward movement, the ozone gas reacts with the activated sludge in the bioreactor mixed water Wr at the interface of the gas phase and the liquid phase, dissolves a part while consuming the ozone gas, and diffuses from the high concentration side to the low concentration side in the bioreactor 4 according to fick's law. In this case, the larger the diameter of the bubbles, the larger the rising speed, and therefore, the rising speed of the bubbles is larger in the case where the exhaust ozone gas is released by dilution in the air, as compared with the case where the exhaust ozone gas is directly released.

As described above, the ozone gas in the bubbles rises while being consumed, and therefore, when the rising speed of the bubbles is large, the concentration difference due to the difference in the height of the film is reduced. Therefore, as shown in fig. 4, when the exhaust ozone gas is discharged by dilution, the change of the dissolved ozone concentration Co with respect to the height becomes smaller than the case of directly discharging the exhaust ozone gas. That is, when the diluted ozone-depleted gas is used, the variation of the dissolved ozone concentration distribution with respect to the height direction of the film is reduced, and the film surface can be relatively uniformly cleaned.

Since the cleaner the membrane surface is, the less resistance the water passes through the membrane, if the membrane surface is cleaned unevenly, the flow rate of the ozone water is biased to the portion of the membrane surface having high cleanliness and the flow rate of the ozone water to the portion of the membrane surface having low cleanliness is insufficient in the reverse cleaning described later. That is, the uniformization of the cleanliness of the film surface also contributes to the improvement of the efficiency of the reverse cleaning. Therefore, it is important to dilute the exhaust ozone gas and use the diluted exhaust ozone gas for membrane surface cleaning to improve the efficiency of reverse cleaning in addition to the irreversible membrane fouling countermeasure.

Again, the description of the project is returned to. When the membrane surface cleaning is continued for the second predetermined time (yes in step S60), the on-off valves 17 and 18 are closed to stop the exhaust ozone gas used for membrane surface cleaning, and the membrane surface cleaning process by the (diluted) exhaust ozone gas is completed (step S70). At this time, the blower 42 is also stopped. As a second step, the circulation pump 15 is operated to resume the generation of ozone water using the gas suction device 14 (step S80).

The ozone water in the second stage is generated by raising the dissolved ozone concentration Co in the ozone water to a concentration required for the back washing. Therefore, strictly speaking, it is preferable to measure the dissolved ozone concentration Co, but in this case, for example, the supply time of the ozone gas, the tank internal pressure, and the like can be used in addition to the measured value of the dissolved ozone concentration Co described later. Therefore, the ozone water production is continued until the end condition is satisfied, with the end condition being whether the resumed ozone water production continues for the third predetermined time (no period in step S90). The condition indicating that the dissolved ozone concentration Co reaches the desired concentration may be, for example, the supply time of the ozone gas, the tank internal pressure, or the like, in addition to the measured value of the dissolved ozone concentration Co described later.

When it is determined that the end condition is satisfied and the desired dissolved ozone concentration Co is obtained (yes in step S90), the ozone water reverse cleaning process is started. First, the three-way valve 45 is switched so that the stopped filter pump 44 communicates with the filtered water pipe 72, and the filtered water delivery pipe 73 is closed. Then, the three-way valve 16 is switched so that the circulation pump 15 communicates with the ozone water supply pipe 25, and a flow path is formed between the liquid phase region Pw of the ozone water generation tank 12 and the secondary side of the filter unit 5. The ozone water in the liquid phase region Pw of the ozone water generation tank 12 is supplied to the secondary side of the filter unit 5, and the reverse cleaning is performed in which the ozone water flows from the secondary side to the primary side, that is, in a direction opposite to the filtration direction with respect to the filtration membrane 51 (step S100). This reverse cleaning is continued until the end condition is satisfied (no in step S110).

The driving force for the transfer of the ozone water to the filter unit 5 and the flow from the secondary side to the primary side of the filter membrane 51 is the gas pressure (in-tank pressure Pt) in the gas phase region Pg including the buffer tank 13. From the viewpoint of the cleaning effect of the filtration membrane 51 or preventing ozone in the ozone water from being released again during the transfer, it is preferable to supply ozone water to the secondary side at a supply pressure as high as possible, but if the pressure applied to the filtration membrane 51 is excessively high, there is a possibility that the filtration membrane 51 is damaged due to exceeding the pressure resistance of the filtration membrane 51. Therefore, for example, it is preferable to control the pressure applied to the filter membrane 51 within an appropriate range by providing a pressure regulating valve, not illustrated. The control pressure is preferably 50kPa or less in view of the balance between the cleaning effect of ozone water and the prevention of breakage of the filtration membrane.

It is considered that the time required for cleaning the filtration membrane 51 depends on the size or degree of contamination of the filtration membrane 51, and is about 30 minutes. Therefore, for example, if the duration of 30 minutes is set as the end condition, if the cleaning is continued for 30 minutes (yes in step S110), the reverse cleaning step is ended (step S120), and the process returns to the raw water filtration step. Specifically, the three-way valve 16 is switched so that the circulation pump 15 communicates with the gas suction device 14 side, and the supply of ozone water to the filter unit 5 is stopped. In this state, the filter pump 44 is activated to supply the water filtered by the filter unit 5 to the ozone water generation tank 12. When a predetermined amount of water is stored in the ozone water generation tank 12, the three-way valve 45 is switched so that the filtrate pump 44 communicates with the filtered water feed pipe 73 side, and the replenishment of filtered water is stopped.

The aeration from the gas diffusion device 41 and the supply of raw water to the biological reaction tank 4 by the blower 42 are restarted, and the filtration is restarted (step S10). Thus, by repeating the filtration step, the ozone water generation step including the membrane surface cleaning step using the diluted exhaust ozone gas, and the ozone water reverse cleaning step, ozone can be effectively used to clean the filtration membrane, and stable water treatment can be performed.

The dissolved ozone concentration Co required for the reverse cleaning is set to a predetermined value near the saturation solubility. Since the higher the dissolved ozone concentration Co, the higher the cleaning effect on the filtration membrane 51, the concentration value is preferably set as close to the saturation solubility as possible. However, since the saturation solubility varies depending on the temperature, pH, and atmospheric pressure of the solvent, a fixed value of, for example, 30mg/L or more may be set as the set concentration value in order to keep the dissolved ozone concentration Co constant in each cleaning. Further, the supply time of the ozone gas at which the dissolved ozone concentration Co reaches the set concentration value may be previously determined, or the supply time may be set in the actual ozone water generation step instead of determining the set concentration value.

Embodiment 2.

In embodiment 1, an example in which the membrane surface cleaning is performed by providing the distal end opening of the ozone exhaust gas pipe directly below the filter unit is described. In embodiment 2, an example in which an exhaust ozone gas pipe is connected to a gas diffusion device for aeration and a diluted exhaust ozone gas for membrane surface cleaning is discharged from the gas diffusion device will be described. Fig. 5 is a schematic diagram showing the configurations of the filtration membrane cleaning apparatus according to embodiment 2 and a water treatment system including the filtration membrane cleaning apparatus, and shows the open/close state of a valve in the step of cleaning the membrane surface, similarly to fig. 1 of embodiment 1. The portions other than the portions before the branching portion of the exhaust ozone gas pipe are the same as those in embodiment 1, and the description of the same portions is omitted. The operation is basically the same as that of embodiment 1, and fig. 2 used for the description of embodiment 1 is referred to, and the description of the same parts is omitted.

In the filtration membrane cleaning apparatus 10 according to embodiment 2 and the water treatment system 1 including the filtration membrane cleaning apparatus 10, as shown in fig. 5, an exhaust ozone gas pipe 23 is connected to a gas diffusion device 41. Thus, the exhaust ozone gas supplied from the ozone water generation tank 12 can be diluted in the gas diffusion device 41 by the aeration air supplied from the blower 42, and discharged from the gas diffusion device 41 to the filter unit 5. With this configuration, the same air bubbles as the inflation air can be made to flow along the membrane surface. That is, in embodiment 1, the front end opening 23x needs to be adjusted to a shape for generating bubbles for membrane surface cleaning, but it may be omitted in embodiment 2.

Further, the provision of the branch portion 46 having the on-off valve 18 used in embodiment 1 may be omitted, and the operation of the on-off valve 18 is not required. For example, in the membrane surface cleaning step using the exhaust ozone gas described in embodiment 1 (steps S50 to S70), the membrane surface cleaning can be started only by operating the on-off valve 17. Specifically, when the on-off valve 17 is opened in step S50 to allow the exhaust ozone gas to flow into the exhaust ozone gas pipe 23, the exhaust ozone gas is diluted with the air for aeration in the gas diffusion device 41, and the diluted exhaust ozone gas can be discharged from the gas diffusion device 41. In step S70, the off-off valve 17 is closed to stop the exhaust ozone gas used for membrane surface cleaning, and the membrane surface cleaning process by diluting the exhaust ozone gas is completed. However, the blower 42 is stopped before the reverse purge.

As described above, in embodiment 2, the number of components can be reduced as compared with embodiment 1, and the operation control can be simplified. In fig. 5, the exhaust ozone gas pipe 23 and the aeration pipe 43 are connected to different connection ports of the gas diffusion device 41, and the exhaust ozone gas is diluted with air in the gas diffusion device 41. The exhaust ozone gas may also be mixed with air before entering the gas diffusion device 41, and may enter the gas diffusion device 41 in a diluted state.

Embodiment 3.

In the above embodiments 1 and 2, the examples of determining whether or not the ozone waste gas for membrane surface cleaning or the ozone water for reverse cleaning can be ensured by time management have been described. In embodiment 3, an example of a structure configured to make a judgment based on the dissolved ozone concentration in the ozone water or the internal pressure of the buffer tank will be described. Fig. 6 and 7 are drawings showing the configurations of a filtration membrane cleaning apparatus according to embodiment 3 and a water treatment system provided with the filtration membrane cleaning apparatus, and a filtration membrane cleaning method, fig. 6 is a schematic diagram showing the configuration of a part of the filtration membrane cleaning apparatus, and fig. 7 is a flowchart showing a filtration membrane cleaning method which is a part related to the cleaning of a filtration membrane in the operation of the water treatment system provided with the filtration membrane cleaning apparatus. The cut end portions of the ozone exhaust gas piping and the other piping are the same as those in embodiment 1 or 2, and the description of the same portions is omitted. Note that, with respect to the operation, the same portions as those in fig. 2 used in the description of embodiment 1 are also omitted.

In the filtration membrane cleaning apparatus 10 according to embodiment 3, as shown in fig. 6, a pressure gauge 81 for measuring the in-tank pressure Pt is provided in the buffer tank 13. In order to measure the dissolved ozone concentration Co in the ozone water in the liquid phase region Pw, a dissolved ozone concentration meter 82 is provided on the upstream side of the gas suction device 14 in the circulation pipe 22. The measured value of the in-tank pressure Pt measured by the pressure gauge 81 and the measured value of the dissolved ozone concentration Co measured by the dissolved ozone concentration meter 82 are output to the control section 30. In embodiment 3, a control unit not shown in embodiments 1 and 2 is described as the control unit 30 in order to clarify the relationship between the measured value and the control.

The operation will be described with reference to fig. 7. In place of step S40 described in embodiment 1, in step S42 of embodiment 3, as a first step, a condition for ensuring completion of generation of ozone water for an exhaust ozone gas is set as whether or not the dissolved ozone concentration Co increases to a first concentration threshold Th_C1The above. That is, as a first step, the generation of ozone water is continued until the dissolved ozone concentration Co increases to the first concentration threshold Th_C1The above. Furthermore, when the concentration Co of the dissolved ozone reaches the first concentration threshold Th_C1In this case, the generation of ozone water in the first stage is completed, and the process is transferred to the membrane surface cleaning step (step S50).

The purpose of the first-stage ozone water generation is to ensure an exhaust ozone gas required for membrane surface cleaning, and it is necessary to confirm the amount of the exhaust ozone gas and the ozone gas concentration. However, if the characteristics of the gas suction device 14 including the flow rate of the circulation pump 15, the characteristics of the ozone gas generation device 11, and the capacities and water amounts of the buffer tank 13 and the ozone water generation tank 12 are grasped, the above can be confirmed based on the dissolved ozone concentration Co. Therefore, compared to the case where time management is simply performed, accurate control can be performed.

On the other hand, as the conditions for terminating the membrane surface cleaning step, in step S62, which is an alternative to step S60 described in embodiment 1, the conditions are determined depending on whether or not the in-tank pressure Pt has decreased to the lower internal pressure limit Th_PThe judgment is made as follows. That is, the membrane surface cleaning is continued until the pressure Pt in the tank is reduced to the lower limit value Th of the internal pressure_PUntil now. When the pressure Pt in the tank decreases to the lower limit value Th of the internal pressure_PIn this case, the supply of the ozone waste gas is stopped, and the generation of ozone water is restarted (step S80).

In the membrane surface cleaning step, it is necessary to confirm the amount of the exhaust ozone gas which is a base of the diluted exhaust ozone gas flowing to the membrane surface. Based on data such as the tank capacity, the normal pressure converted volume of the exhaust ozone gas supplied to the filter unit 5 can be easily confirmed from the change in the tank internal pressure Pt. That is, a predetermined volume of the exhaust ozone gas can be used for membrane surface cleaning. Further, for example, in the case of simply performing time management, when the in-tank pressure Pt is lower than the pressure required for bubbling in the filter unit 5 for the time, it is assumed that bubbling is performed only with air containing no ozone for the remaining time. However, if pressure management is performed, this can be reliably avoided.

As conditions for terminating the generation of the second stage of ozone water, in step S92, which is an alternative to step S90 described in embodiment 1, it is determined whether or not the dissolved ozone concentration Co has increased to be higher than the first concentration threshold Th_C1Second concentration threshold value Th_C2The above. That is, when the dissolved ozone concentration Co increases to be greater than the firstConcentration threshold Th_C1Second concentration threshold value Th_C2In this case, the ozone water generation in the second stage is finished, and the process is transferred to the back washing process (step S100).

The purpose of the ozone water generation in the second stage is to ensure the dissolved ozone concentration Co in the ozone water required for the back washing, and as in the present embodiment, the dissolved ozone concentration Co can be accurately controlled by measuring it.

That is, by measuring the dissolved ozone concentration Co, it is possible to more reliably generate an ozone waste gas suitable for membrane surface cleaning and an ozone water suitable for reverse cleaning. Further, by measuring the in-tank pressure Pt, the membrane surface cleaning can be performed using an appropriate amount of the exhaust ozone gas.

Embodiment 4.

In each of embodiments 1 to 3 described above, an example of determining whether or not the filtering process or the reverse cleaning should be ended based on time has been described. In embodiment 4, an example in which the determination is made based on the pressure difference between membranes of the filtration membrane will be described. Fig. 8 and 9 are drawings showing the configuration of a filtration membrane cleaning apparatus according to embodiment 4, a water treatment system including the filtration membrane cleaning apparatus, and a filtration membrane cleaning method, fig. 8 is a schematic diagram showing the configuration of a water treatment system including the filtration membrane cleaning apparatus, and fig. 9 is a flowchart showing a filtration membrane cleaning method, which is a part related to cleaning of a filtration membrane in an operation of a water treatment system including the filtration membrane cleaning apparatus. The measurement of the inter-membrane pressure difference and the operation control using the measured value of the inter-membrane pressure difference are the same as those in embodiment 3, and the description of the same portions is omitted.

In the water treatment system 1 according to embodiment 4, a pressure gauge 83 is provided in the filtered water pipe 72 as shown in fig. 8 in order to measure the pressure difference between membranes. The pressure of the filtered water pipe 72 measured by the pressure gauge 83 is output to the control unit 30. The pressure gauge 83 does not directly measure the pressure difference between the membranes but measures the pressure on the secondary side of the filter membrane 51, but since the primary side can be regarded as atmospheric pressure, it can be evaluated as the pressure difference between the membranes. Further, since the filtered water pipe 72 communicates with the ozonated water supply pipe 25, the pressure applied to the ozonated water supply pipe 25 during the backwashing, that is, the pressure difference between membranes can be measured by the pressure gauge 83.

The operation will be described with reference to fig. 9. In place of step S20 described in embodiment 1, in step S22 of embodiment 4, the end condition of the filtration step is set as whether or not the differential pressure applied to the filtration membrane 51 during filtration (the pressure difference Δ P between membranes) exceeds the upper limit Th_ΔM. That is, the filtration step is continued until the pressure difference Δ P between the membranes exceeds the upper limit value Th_ΔM. When the pressure difference Δ P between the membranes exceeds the upper limit Th_ΔMIn this case, the process proceeds to the ozone water generation step (step S30).

In the filtration step of removing organic matter from the primary mixed water Wr and passing only water through the secondary side, activated sludge or the like is deposited on the surface of the primary side of the filtration membrane 51 as the filtration proceeds as described with reference to fig. 3, thereby forming a cake layer. As the cake layer is formed, the pressure loss when water passes from the primary side to the secondary side of the filtration membrane 51, that is, the pressure difference Δ P between membranes increases. The increase in the inter-membrane pressure difference Δ P not only leads to a decrease in the amount of treatment per hour but also leads to an increase in damage to the filtration membrane 51, and therefore management of the inter-membrane pressure difference Δ P is important. By measuring the pressure difference Δ P between membranes as in the present embodiment, accurate control can be performed in terms of water treatment efficiency and facility management.

In addition, regarding the conditions for terminating the backwashing, in step S112, which is an alternative to step S110 described in embodiment 1, it is set whether or not the differential pressure (pressure difference Δ P between membranes) applied to the filtration membrane 51 during backwashing in which ozone water passes from the secondary side to the primary side is reduced to the lower limit Th_ΔWThe following. That is, the reverse cleaning process is continued until the pressure difference Δ P between the membranes is reduced to the lower limit value Th_ΔWThe following. When the pressure difference Δ P between the membranes is decreased to the lower limit value Th_ΔWThereafter, the reverse cleaning is terminated (step S120), and the process proceeds to the filtering step (step S10).

The purpose of the back washing is to remove a cake layer accumulated on the membrane surface or organic substances accumulated in the pores 51p of the filtration membrane 51 in the filtration process and to wash the filtration membrane 51. Therefore, contrary to the filtration process, it is important to reduce the inter-membrane pressure difference Δ P to a small extent, and as in the present embodiment, accurate control can be performed by measuring the inter-membrane pressure difference Δ P.

In steps S22 and S112, both are referred to as the inter-membrane pressure difference Δ P, and the inter-membrane pressure difference Δ P in the filtration step is a pressure difference accompanied by a pressure loss when flowing from the primary side to the secondary side, and the secondary side is a negative pressure. On the other hand, the inter-membrane pressure difference Δ P in the reverse cleaning step is a pressure difference due to a pressure loss when flowing from the secondary side to the primary side, and the secondary side is a positive pressure. Therefore, the upper limit Th_ΔMAnd a lower limit value Th_ΔWThe positive and negative of (1) are opposite, and simple comparison cannot be performed, but the upper limit value Th is set_ΔMIs greater than the lower limit value Th_ΔWDivided by the hourly flow rate during the reverse purge. In any case, by measuring the pressure difference Δ P between the membranes and judging whether or not to end based on the measured value, the end of the filtration process and the end timing of the reverse washing can be accurately controlled.

In the above description, embodiment 3 is described as adding components or operations for measuring the pressure difference between membranes. However, the present invention is not necessarily limited to this, and components or operations for measuring the pressure difference between membranes may be added to the embodiment described in embodiment 1 or 2.

Embodiment 5.

In each of embodiments 1 to 4, the mode in which the filtration step is switched to the membrane surface cleaning step or the reverse cleaning step has been described with attention being paid to one filtration unit. In embodiment 5, focusing on the fact that the filter unit is composed of a plurality of filters, a mode of adjusting the switching of the process according to the state of each filter will be described. Fig. 10 is a schematic diagram showing a configuration in which the filtration membrane cleaning apparatus, the configuration of a water treatment system including the filtration membrane cleaning apparatus, and the filtration membrane cleaning method according to embodiment 5 are controlled by shifting the switching timing of the process for each of a plurality of filters. In the drawings, a part related to generation or storage of ozone water in the filtration membrane cleaning apparatus is omitted, and only a piping part near the filtration unit is shown.

In each of embodiments 1 to 4, the single filtration unit 5 is focused on for explanation, and therefore, the flow chart shows that the filtration step, the membrane surface cleaning step, and the reverse cleaning step are performed when other steps are not performed. However, as shown in embodiment 5, there may be a case where one filtration membrane cleaning apparatus 10 is connected to a filtration unit 5 including a plurality of filters 5a to 5d that can be independently controlled. In this case, in the case of the method of performing the membrane cleaning by shifting the time for each of the filters 5a to 5d, the step of generating ozone water may be performed simultaneously with the filtering step, the membrane surface cleaning step, and the backwashing step.

Therefore, in the flowcharts used in the operation descriptions of embodiments 1 to 4, the operation contents of the respective steps are the same, but the order of the steps is parallel operation. On the other hand, the sequence of the filtration step, the membrane surface cleaning step, and the reverse cleaning step of one filter is explained by the same contents as those explained in the flowcharts used in the operation explanation of embodiments 1 to 4, except for the portion where ozone water is generated.

In the water treatment system 1 according to embodiment 5, as shown in fig. 10, a combination of four filters 5a to 5d and gas diffusion devices 41a to 41d located directly below the filters 5a to 5d is provided in the biological reaction tank 4. Therefore, in the filtered water pipe 72 for pumping out the filtered treated water, the branch pipes 72a to 72d branched by the on-off valves 65a to 65d are connected to the filters 5a to 5d, respectively. In the ozone water supply pipe 25 for supplying ozone water for back washing, the branch pipes 25a to 25d branched by the on-off valves 66a to 66d are also connected to the branch pipes 72a to 72d, respectively. Pressure gauges 83a to 83d for measuring the pressure difference Δ P between the membranes of the filters 5a to 5d are connected to the branch pipes 72a to 72d, respectively.

Similarly, in the inflation pipe 43 for supplying inflation air, branch pipes 43a to 43d branched by the on-off valves 47a to 47d are connected to the gas diffusion devices 41a to 41d, respectively. In the exhaust ozone gas pipe 23 for supplying the exhaust ozone gas for membrane surface cleaning, branch pipes 23a to 23d branched by the on-off valves 17a to 17d are also connected to the branch pipes 43a to 43d, respectively.

Although not shown, in embodiment 5, the three- way valves 16 and 45 described in the configurations of embodiments 1 to 4 are replaced with a combination of branched pipes and on-off valves that switch the opening and closing of each branched portion, for example. For example, taking the three-way valve 16 as an example, the three-way valve is replaced with a T-shaped pipe branched from the circulation pump 15 to the gas suction device 14 side and the ozone water supply pipe 25, and the above-described on-off valves 66a to 66d are provided on the ozone water supply pipe 25 side. Therefore, the mode described as "switching only" between circulation in the circulation pipe 22 and supply to the ozone water supply pipe 25 side is replaced with a mode in which the circulation is based and supply of ozone water can be performed "in parallel".

The operation will be described based on the above configuration. In fig. 10, in the filter 5a and the filter 5b, the on-off valves 47a, 47b are opened (white), the on-off valves 17a, 17b are closed (black), and air for inflation is discharged from the gas diffusion device 41a directly below. Since the switching valves 65a and 65b are opened and the switching valves 66a and 66b are closed, the secondary side is made negative by the suction pump 44, and the bioreactor mixed water Wr flows from the primary side to the secondary side. That is, the filtration step of filtering the mixed water Wr in the biological reaction tank is performed in the filters 5a and 5 b.

On the other hand, in the filter 5c, the on-off valve 47c and the on-off valve 17c are both opened, and a diluted exhaust ozone gas in which the exhaust ozone gas and air are mixed is discharged from the gas diffusion device 41a directly below. Since the on-off valves 65c and 66c are closed, no flow occurs between the primary side and the secondary side. That is, in the filter 5c, membrane surface cleaning is performed by diluting the exhaust ozone gas.

In the filter 5d, both the on-off valve 47d and the on-off valve 17d are opened and closed, and bubbles are not discharged from the gas diffusion device 41a directly below. Since the on-off valve 65d is closed and the on-off valve 66d is opened, the ozone water from the ozone water generation tank 12 is supplied to the secondary side of the filter 5 d. That is, the back washing with ozone water is performed in the filter 5 d.

Here, in the filters 5a and 5b that perform the filtration process, the inter-membrane pressure difference Δ P at the time of filtration is evaluated based on the measurement values of the pressure gauges 83a and 84b, respectively, and it is determined whether or not the filtration process should be continued, for example, as described in step S22 of embodiment 4. After the filtration step is completed, the process proceeds to a membrane surface cleaning step.

Similarly, in the filter 5d for performing the reverse cleaning process, the pressure difference Δ P between the membranes at the time of the reverse cleaning is evaluated based on the measurement value of the pressure gauge 83d, and, for example, as explained in step S112, it is judged whether or not the reverse cleaning process should be continued. After the reverse phase washing step is completed, the process proceeds to a filtration step. In the filter 5c that performs the membrane surface cleaning, for example, as described in step S60 of embodiment 1, it is determined whether or not the membrane surface cleaning process should be continued based on the duration. When the membrane surface cleaning process is completed, the process proceeds to a reverse cleaning process.

While the above-described steps are repeated individually for each of the filters 5a to 5d, the ozone water is generated substantially continuously. Specifically, while the circulation pump 15 is in operation, water or ozone water circulates in the circulation pipe 22 regardless of the state of communication with the ozone water supply pipe 25. That is, ozone water is appropriately generated in any of the filters 5a to 5d to prevent a shortage of the ozone water required for the membrane surface cleaning and the ozone water required for the reverse cleaning. While the filter pump 44 is operating, the filtered water after treatment is supplied to the filtered water tank through the filtered water supply pipe 73 regardless of whether filtered water is supplied to the ozone water generation tank 12.

With this configuration, when the filters 5a to 5d have different cake deposition states, or when the filters 5a to 5d have different filtration performances, the cleaning treatment including the surface cleaning and the back cleaning is performed in an optimum cycle according to the properties of the filters 5a to 5d, and the water treatment can be performed efficiently. Of course, when the properties of each of the filters 5a to 5d are the same and the state of the mixed water Wr in the biological reaction tank to be treated is stable, the respective steps can be controlled by time control. In the case of time management, for example, if any one of the plurality of filters 5a to 5d is set to be necessary to perform the filtering process, the treatment of the bio-reactor mixed water Wr can be continuously performed without stagnation.

That is, as shown in embodiment 5, if the step can be individually set for each of the plurality of filters 5a to 5c, stable water treatment can be performed. Although embodiment 5 shows an example in which 4 filters 5a to 5d are used, the number of filters is not limited to 4, and any filter having 2 or more filters can be used.

For example, the control unit 30, the control unit of the water treatment system not shown, or a control unit integrating these units is referred to as hardware 3, and as an example, the hardware 3 is configured by a processor 31 and a storage device 32 as shown in fig. 11. Although not shown, the storage device includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. In addition, an auxiliary storage device such as a hard disk may be provided instead of the flash memory. The processor 31 executes a program input from the storage device 32. In this case, the program is input from the auxiliary storage device to the processor 31 via the volatile storage device. The processor 31 may output data such as the operation result to a volatile storage device of the storage device 32, or may store the data in an auxiliary storage device via the volatile storage device.

As described in the embodiments, by using the membrane surface cleaning using the diluted exhaust ozone gas of the present invention, the utilization efficiency of ozone gas can be improved with a simple configuration without increasing the size of the apparatus or adding equipment. In particular, since the diluted ozone gas is discharged as bubbles into the bioreactor tank 4 instead of the exhaust ozone gas itself for membrane surface cleaning, irreversible membrane fouling does not occur, and the degree of membrane fouling can be reliably reduced.

Further, since the ozone-containing waste gas used for membrane surface cleaning is consumed in the biological reaction tank 4 and ozone is consumed before the ozone water used for reverse cleaning flows out to the primary side of filtration, a device for treating excess ozone gas using a reduction device such as a catalyst or activated carbon is not required, and the device can be prevented from being enlarged and the cost can be prevented from being increased. Further, since the degree of contamination of the filtration membrane by the exhaust ozone gas is reduced before the reverse cleaning, the time required for the reverse cleaning can be shortened, and the amount of generation of ozone gas required for the cleaning can be reduced.

Although various exemplary embodiments and examples have been described in the present application, the various features, modes, and functions described in 1 or more embodiments are not limited to the application to a specific embodiment, and may be applied to the embodiments alone or in various combinations. Therefore, it is considered that numerous modifications not illustrated are also included in the technical scope disclosed in the present specification. For example, the present invention includes a case where at least one of the components is modified, added, or omitted, and a case where at least one of the components is extracted and combined with the components of the other embodiments.

Thus, the filtration membrane cleaning apparatus 10 according to each embodiment includes: a storage unit (gas suction device 14, ozone water generation tank 12, and buffer tank 13) that dissolves ozone gas in water to generate ozone water and stores the generated ozone water and a by-product exhaust ozone gas; a reverse cleaning mechanism (ozone water generation tank 12, circulation pump 15) for performing reverse cleaning of the filter unit 5 provided in the biological reaction tank 4 for filtering raw water, the reverse cleaning causing ozone water taken out from the storage unit to flow from the secondary side to the primary side of the filter membrane 51; membrane surface cleaning means (ozone water generation tank 12, buffer tank 13, gas diffusion device 41) for discharging bubbles containing ozone in biological reaction tank 4 and cleaning the membrane surface by making the discharged bubbles flow along the surface on the primary side (primary side surface 51f1) of filtration membrane 51; a control unit 30 for controlling the operations of the reverse cleaning mechanism and the membrane surface cleaning mechanism so that the membrane surface is cleaned by the membrane surface cleaning mechanism before the reverse cleaning by the reverse cleaning mechanism; and an exhaust ozone gas diluting part (blower 42) for diluting the exhaust ozone gas and supplying the exhaust ozone gas to the membrane surface cleaning mechanism, wherein the exhaust ozone gas is taken out from the storage part as a gas discharged as bubbles, so that the ozone can be effectively used to effectively clean the filtration membrane without irreversible membrane contamination.

In particular, since the waste ozone gas dilution part dilutes the waste ozone gas taken out from the storage part to 1.4 times or more or dilutes the ozone concentration thereof to 150g/m³As a result, irreversible membrane fouling can be reliably prevented, and the filtration membrane can be cleaned efficiently.

If the membrane surface cleaning means is connected to the gas diffusion device 41 for aerating the raw water stored in the biological reaction tank 4 and bubbles are discharged from the gas diffusion device 41, the addition of the components can be omitted.

Further, since the filter apparatus includes the pressure gauge 83, the pressure gauge 83 measures a differential pressure between the primary side and the secondary side (inter-membrane differential pressure Δ P) when the fluid is caused to flow between the primary side and the secondary side of the filter membrane 51, and the control unit 30 determines whether or not to start the reverse cleaning or whether or not to end the reverse cleaning based on the measured differential pressure, efficient filtration processing can be realized.

Further, in the water treatment system including the biological reaction tank 4 for storing raw water for the filtration treatment, the filtration unit 5 provided in the biological reaction tank 4 for performing the filtration treatment on the raw water, and the above-described filtration membrane cleaning apparatus 10 for cleaning the filtration membrane 51 of the filtration unit 5, the filtration membrane 51 is effectively maintained, and the filtration treatment capability is improved.

The filter unit 5 is configured by a plurality of filters 5a to 5d that independently perform filtration treatment of raw water, and the plurality of filters each have a pressure gauge 83a to 83d that measures a pressure difference (inter-membrane pressure difference Δ P) between the primary side and the secondary side when a fluid is caused to flow between the primary side and the secondary side of the filter membrane 51 of the filter, and the control unit 30 can effectively treat the filter membrane 51 when the filter having a large rate of increase of the pressure difference among the plurality of filters is set as a priority for membrane surface cleaning and reverse cleaning.

Further, a method for cleaning a filtration membrane according to each embodiment includes: a storage step (steps S30, S80) of dissolving ozone gas in water to generate ozone water, and storing the generated ozone water and a by-product ozone exhaust gas; a membrane surface cleaning step (step S50) of allowing bubbles containing ozone gas to flow along a primary surface (primary side surface 51f1) of the filtration membrane 51 toward the filtration unit 5 for filtering raw water; and a reverse cleaning step (step S100) of taking out the ozone water stored in the storing step and allowing the taken-out ozone water to flow from the secondary side to the primary side of the filtration membrane 51, wherein the ozone-containing waste gas stored in the storing step is diluted and flows as bubbles in the membrane surface cleaning step, so that ozone can be effectively used and the filtration membrane can be cleaned without irreversible membrane contamination.

Specifically, in the membrane surface cleaning step, the stored waste ozone gas is diluted to 1.4 times or more, or the ozone concentration thereof is diluted to 150g/m³As a result, irreversible membrane fouling can be reliably prevented, and the filtration membrane can be cleaned efficiently.

Description of the reference symbols

1: a water treatment system; 4: a biological reaction tank; 5: a filtration unit; 5a to 5 d: a filter; 10: a filtration membrane cleaning device; 11: ozone gas generating device an ozone gas generating device; 12: an ozone water generating tank; 13: a buffer tank; 14: a gas suction device; 15: a circulation pump; 16: (for ozone water) three-way valve; 17. 17a to 17 d: (for waste ozone gas) on-off valve; 18: (for dilution) on-off valve; 22: a circulation piping; 23: an exhaust ozone gas piping; 23a to 23 d: a branch piping; 23 x: a front end opening part; 24: a filtered water supply pipe and a filtered water supply pipe; 25: an ozone water supply pipe; 25a to 25 d: a branch piping; 30: a control section; 41. 41a to 41 d: a gas diffusion device; 42: a blower; 43: a piping for inflation; 43a to 43 d: a branch piping; 44: a filter pump; 45: a three-way valve (for filtering water); 51: a filtration membrane; 51f 1: a primary side; 51 p: fine pores; 65a to 65 d: (for switching filtered water) on-off valve; 66a to 66 d: (for ozone water switching) a switching valve; 71: raw waterPiping; 72: a filtered water pipe; 72a to 72 d: a branch piping; 73: a filtered water delivery piping; 81: a pressure gauge; 82: a dissolved ozone concentration meter; 83. 83a to 83 d: (for measuring the pressure difference between membranes) pressure gauge; 90: an organic matter; co: the concentration of dissolved ozone; pg: a gas phase zone; pt: the pressure in the tank; pw: a liquid phase region; th_C1: a first concentration threshold value (of dissolved ozone concentration at the time of determining the start of membrane surface cleaning); th_C2: a second concentration threshold value (of the dissolved ozone concentration at the time of the start judgment of the reverse cleaning); th_P: an internal pressure lower limit value (of the buffer tank pressure at the time of determination of the completion of membrane surface cleaning); th_ΔM: an upper limit value (of the pressure difference between membranes at the time of filtration); th_Δw: lower limit value (of pressure difference between membranes at the time of judgment of completion of reverse cleaning); wr: mixing water in a biological reaction tank; Δ P: the pressure difference between the membranes.

Claims (8)

1. A filtration membrane cleaning apparatus, comprising:

a storage unit that dissolves ozone gas in water to generate ozone water and stores the generated ozone water and a by-product ozone-containing waste gas;

a reverse cleaning mechanism that performs reverse cleaning of a filter unit provided in the biological reaction tank for filtering raw water, the reverse cleaning causing ozone water taken out of the storage unit to flow from a secondary side to a primary side of the filter membrane;

a membrane surface cleaning mechanism that performs membrane surface cleaning that discharges bubbles containing ozone in the biological reaction tank and causes the discharged bubbles to flow along a surface on a primary side of the filtration membrane;

a control unit that controls operations of the reverse cleaning mechanism and the membrane surface cleaning mechanism so that the membrane surface is cleaned by the membrane surface cleaning mechanism before the reverse cleaning by the reverse cleaning mechanism; and

and an exhaust ozone gas diluting section for diluting an exhaust ozone gas taken out from the storing section as a gas discharged as the bubbles and supplying the exhaust ozone gas to the membrane surface cleaning mechanism.

2. The filtration membrane cleaning apparatus according to claim 1,

the waste ozone gas diluting part is used for diluting the waste ozone gas taken out from the storage part to more than 1.4 times, or diluting the ozone concentration to 150g/m³The following.

3. The filtration membrane cleaning apparatus according to claim 1 or 2,

the membrane surface cleaning mechanism is connected with a gas diffusion device, the bubbles are discharged from the gas diffusion device, and the gas diffusion device is used for aerating raw water stored in the biological reaction tank.

4. The filtration membrane cleaning apparatus according to any one of claims 1 to 3,

comprises a pressure gauge for measuring a pressure difference between a primary side and a secondary side when a fluid is caused to flow between the primary side and the secondary side of the filter membrane,

the control unit determines whether to start the reverse washing or not and whether to end the reverse washing or not, based on the measured differential pressure.

5. A water treatment system, comprising:

a biological reaction tank which stores raw water;

the filtering unit is arranged in the biological reaction tank and is used for filtering the raw water; and

the filtration membrane cleaning apparatus according to any one of claims 1 to 4, which is used for cleaning a filtration membrane of the filtration unit.

6. The water treatment system of claim 5,

the filtration unit is composed of a plurality of filters that independently perform filtration treatment of the raw water, and each of the plurality of filters has a pressure gauge that measures a pressure difference between a primary side and a secondary side when a fluid is caused to flow between the primary side and the secondary side of a filtration membrane of the filter,

the control unit sets a filter having a large rising speed of the differential pressure among the plurality of filters as a priority target for the membrane surface cleaning and the reverse cleaning.

7. A method for cleaning a filtration membrane, comprising:

a storage step of dissolving ozone gas in water to generate ozone water, and storing the generated ozone water and an exhaust ozone gas as a by-product;

a membrane surface cleaning step of causing bubbles containing ozone gas to flow along a surface of a primary side of a filtration membrane to a filtration unit for filtering raw water; and

a reverse cleaning step of taking out the ozone water stored in the storing step and allowing the taken-out ozone water to flow from the secondary side to the primary side of the filtration membrane,

in the membrane surface cleaning step, the exhaust ozone gas stored in the storing step is diluted and then flowed as the bubbles.

8. The filtration membrane cleaning method according to claim 7,

in the membrane surface cleaning step, the stored waste ozone gas is diluted to 1.4 times or more, or the ozone concentration thereof is diluted to 150g/m³The following.

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