Filtration membrane cleaning equipment

Abstract

A filtration membrane cleaning device that efficiently removes both contaminants adhering to the surface of the filtration membrane on the side of the permeate flow path and contaminants adhering to the pores of the filtration membrane. The filtration membrane cleaning device cleans the filtration membrane of a filtration membrane module (3) equipped with a first water collection port (36) and a second water collection port (37) for extracting membrane-filtrated water (19) that has permeated the filtration membrane, and includes a controller that controls a first cleaning water pump (22), a first switching valve (12), a circulation switching valve (11), and a circulation pump (32) to perform one of two cleaning methods selected from dead-end filtration cleaning, in which the first cleaning water (21) is used as cleaning water and the first cleaning water tank (20) is used as the cleaning water tank, and cleaning water from the cleaning water tank is supplied to both the first water collection port (36) and the second water collection port (37), and cross-flow filtration cleaning, in which cleaning water extracted from the second water collection port (37) is circulated through a circulation flow path formed by a circulation pipe (30) and a cleaning water pipe (4) and supplied to the first water collection port (36).

Description

Technical Field

[0001] This application relates to a filtration membrane cleaning device.

Background Art

[0002] As a method for separating suspended substances in treated water, membrane filtration using a filtration membrane is used. For example, in the treatment of sewage or industrial wastewater, after the treated water is treated by the activated sludge method, suspended substances are separated and removed using a filtration membrane. Generally, cylindrical or sheet-like microfiltration membranes or ultrafiltration membranes are used as the filtration membrane. As the filtration method, there are an external pressure filtration method in which the treated water is passed outside the cylindrical or sheet-like filtration membrane and the filtered water is passed inside, and an internal pressure filtration method in which the treated water is passed inside the cylindrical filtration membrane and the filtered water is passed outside. Further, as a method for collecting the filtered water, there are single-end water collection in which water is collected from one water collection port of the filtration membrane, and both-end water collection in which water is collected from two water collection ports of the filtration membrane.

[0003] In such membrane filtration using a filtration membrane, there is a problem that the filtration performance deteriorates with continuous use of the filtration membrane. Specifically, with continuous use of the filtration membrane, on the surface of the filtration membrane in contact with the treated water (the outer surface of the filtration membrane in the external pressure filtration method, the inner surface of the filtration membrane in the internal pressure filtration method), on the surface of the filtration membrane in contact with the filtered water (the inner surface of the filtration membrane in the external pressure filtration method, the outer surface of the filtration membrane in the internal pressure filtration method), or in the pores of the filtration membrane, dirt adheres and clogging occurs, and the filtration performance gradually deteriorates. In particular, when clogging occurs in the filtration membrane, the pressure required for filtration increases, so the membrane filtration flux (the amount of membrane filtration water per unit membrane area per unit time) also decreases. Therefore, in order to maintain the performance of the filtration membrane, it is necessary to clean the filtration membrane regularly.

[0004] To maintain filtration performance, backflow cleaning is performed by passing cleaning water, such as filtered water or clarified water, through the filter membrane from the secondary side opposite to the primary side of the filter membrane. This physically removes pollutants adhering to the surface of the filter membrane that comes into contact with the treated water. Furthermore, to enhance the cleaning effect of the filter membrane, a method has been proposed in which backflow cleaning of the filter membrane is performed using cleaning water containing an oxidizing agent such as sodium hypochlorite (also called "sodium hypochlorite") or ozone. This oxidizes and decomposes pollutants chemically attached to the surface of the filter membrane or within its pores by intermolecular forces, etc., that come into contact with the filtered water. When passing cleaning water, such as filtered water or clarified water, through the filter membrane from the secondary side opposite to the primary side, the method of passing the cleaning water differs depending on the filtered water collection method described above. For filter membranes with single-end collection, cleaning is performed by dead-end filtration (total filtration), where cleaning water is supplied from a single collection port on the filter membrane. For filter membranes with water collection at both ends, cleaning can be performed by dead-end filtration, which supplies cleaning water from two water collection points on the filter membrane, or by cross-flow filtration (parallel filtration), which supplies cleaning water from one water collection point on the filter membrane and discharges the supplied cleaning water from the other water collection point. For example, in cross-flow filtration, a cleaning method has been proposed in which pollutants adhering to the surface of the filter membrane are removed by repeatedly increasing and decreasing the amount of cleaning water supplied, causing the filter membrane to expand and contract (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 5473897 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the filtration membrane cleaning apparatus described in Patent Document 1, cleaning is performed by cross-flow filtration of cleaning water. Because the cleaning water continues to flow through the permeate channel of the filtration membrane, the cleaning water is uniformly distributed throughout the filtration membrane, effectively removing contaminants attached to the surface of the filtration membrane on the permeate channel side. However, since only a portion of the cleaning water permeates to the primary side of the filtration membrane, there is a problem that the efficiency of removing contaminants attached to the pores of the filtration membrane is lower compared to cleaning by dead-end filtration, where the entire amount of cleaning water permeates to the primary side of the filtration membrane.

[0007] This invention was made to solve the above-mentioned problems and aims to provide a filter membrane cleaning device that efficiently removes both contaminants adhering to the surface of the filter membrane on the permeate flow path side and contaminants adhering to the pores of the filter membrane. [Means for solving the problem]

[0008] The filtration membrane cleaning apparatus disclosed herein is a filtration membrane cleaning apparatus for cleaning the filtration membrane of a filtration membrane module equipped with a first water collection port and a second water collection port, which are two water collection ports for extracting membrane filtered water that has permeated through the filtration membrane. The system includes a controller that controls the selection between dead-end filtration cleaning and cross-flow filtration cleaning for cleaning the filtration membrane. When dead-end filtration cleaning is selected, the controller controls the supply of cleaning water to both the first and second collection ports. When cross-flow filtration cleaning is selected, the controller controls the supply of cleaning water to the first collection port and discharge it from the second collection port. [Effects of the Invention]

[0009] The filtration membrane cleaning apparatus disclosed herein is a filtration membrane cleaning apparatus for cleaning the filtration membrane of a filtration membrane module equipped with a first water collection port and a second water collection port, which are two water collection ports for extracting membrane filtered water that has permeated through the filtration membrane. The system includes a controller that controls the selection between dead-end filtration cleaning and cross-flow filtration cleaning for cleaning the filtration membrane. When dead-end filtration cleaning is selected, the controller controls the supply of cleaning water to both the first and second collection ports. When cross-flow filtration cleaning is selected, the controller controls the supply of cleaning water to the first collection port and discharge it from the second collection port. Therefore, both contaminants adhering to the surface of the filter membrane on the permeate flow path side and contaminants adhering to the pores of the filter membrane can be efficiently removed. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows the configuration of a water treatment system equipped with a filtration membrane cleaning device according to Embodiment 1. [Modes for carrying out the invention]

[0011] The following describes in detail, with reference to the drawings, a filtration membrane cleaning apparatus according to an embodiment for carrying out the present invention. In each figure, the same reference numerals indicate the same or corresponding parts.

[0012] Embodiment 1. Figure 1 shows the configuration of a water treatment system 100 equipped with a filtration membrane cleaning device according to Embodiment 1. The water treatment system 100 comprises a water tank 2 for containing water to be treated 1, a filtration membrane module 3 for membrane filtration treatment of water to be treated 1, a membrane filtration water tank 18 for containing membrane-filtered water 19, and a filtration membrane cleaning device.

[0013] The water tank 2 is equipped with a water treatment pipe 5 that supplies water to be treated 1, and the water to be treated 1 is subjected to membrane filtration treatment in the water tank 2 by a filtration membrane module 3. The water to be treated 1 can be, for example, tap water, sewage, secondary treated sewage water, industrial wastewater, seawater, or human waste. The water tank 2 is connected to a sludge extraction pipe 10 and an air pipe 7, and an aeration device 8 is located at the bottom of the water tank 2. A blower 6 is connected to the aeration device 8 via the air pipe 7 and is used to air-clean the membrane surface of the filtration membrane of the filtration membrane module 3. The sludge extraction pipe 10 is equipped with a sludge extraction pump 9 for extracting sludge.

[0014] The filtration membrane module 3 includes a filtration membrane and two water collection ports, a first water collection port 36 and a second water collection port 37, which collect the membrane-filtered water that has permeated through the filtration membrane from both ends of the flow path inside the filtration membrane. The material of the filtration membrane of the filtration membrane module 3 does not need to be degraded by oxidizing agents. The material of the filtration membrane of the filtration membrane module 3 may be, for example, polyolefins such as polyethylene, polypropylene, and polybutene; fluorine-based resin compounds such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE); celluloses such as cellulose acetate and ethylcellulose; and ceramics. Alternatively, the material of the filtration membrane of the filtration membrane module 3 may be a combination of two or more of the above substances. The material of the filtration membrane in the filtration membrane module 3 is preferably a fluororesin compound that has excellent resistance to strong oxidizing agents such as ozone.

[0015] The type of filtration membrane in the filtration membrane module 3 is not particularly limited, and known filtration membranes such as microfiltration (MF) membranes and ultrafiltration (UF) membranes may be used. The average pore size of the filtration membrane in the filtration membrane module 3 is not particularly limited, but is preferably 0.001 μm or more and 1 μm or less, more preferably 0.01 μm or more and 0.1 μm or less. If the filtration membrane has an average pore size in this range, the filtration membrane cleaning device of the water treatment system 100 can efficiently remove not only pollutants attached to the surface of the filtration membrane in contact with the water to be treated 1, but also pollutants chemically attached to the surface of the filtration membrane in contact with the membrane filtered water 19, and pollutants attached to the pores of the filtration membrane. The shape of the filtration membrane in the filtration membrane module 3 is not particularly limited, and may be a known shape such as cylindrical or flat membrane. The filtration membrane in the filtration membrane module 3 may be immersion type, casing type, or monolith type. The filtration method of the filtration membrane module 3 may be either a dead-end filtration method or a cross-flow filtration method. The water flow method for the filtration membrane of the filtration membrane module 3 is not particularly limited and may be either an external pressure filtration method in which the water to be treated 1 flows outside the filtration membrane and the filtered water 19 flows inside the filtration membrane, or an internal pressure filtration method in which the water to be treated 1 flows inside the filtration membrane and the filtered water 19 flows outside the filtration membrane. The water collection method for the filtration membrane module 3 is double-ended collection, where water is collected from two collection ports, the first collection port 36 and the second collection port 37.

[0016] One end of the cleaning water pipe 4 is connected to the membrane filtered water pipe 14 by a circulation switching valve 11, and the other end is connected to the first water collection port 36. One end of the circulation pipe 30 is connected to the membrane filtered water pipe 14 and the cleaning water pipe 4 by a circulation switching valve 11, and the other end is connected to the second water collection port 37. It includes a circulation pump 32 for circulating the cleaning water, a circulation flow rate meter 31 for measuring the flow rate of the circulating cleaning water, and an air vent switching valve 33. The air vent switching valve 33 is connected to the air vent pipe 34. One end of the membrane filtered water pipe 14 is connected to the cleaning water pipe 4 and the circulation pipe 30 by a circulation switching valve 11, and the other end is connected to a membrane filtered water tank 18 that contains membrane filtered water 19. It includes a membrane filtered pump 15, a membrane filtered water flow rate meter 16, and a membrane filtered water pressure gauge 17.

[0017] The first wash water piping 24 has one end connected to the membrane filtration water piping 14 by a first switching valve 12, and the other end connected to the first wash water tank 20. The first wash water piping 24 includes a first wash water pump 22 for supplying the first wash water 21 contained in the first wash water tank 20 to the filtration membrane of the filtration membrane module 3, and a first wash water flow rate meter 23 for measuring the flow rate of the first wash water 21. The second wash water piping 29 has one end connected to the membrane filtration water piping 14 by a second switching valve 13, and the other end connected to the second wash water tank 25. The second wash water piping 29 includes a second wash water pump 27 for supplying the second wash water 26 contained in the second wash water tank 25 to the filtration membrane of the filtration membrane module 3, and a second wash water flow rate meter 28 for measuring the flow rate of the second wash water 26.

[0018] The types of chemicals contained in the first wash water 21 and the second wash water 26 are not particularly limited as long as they are chemicals that decompose organic or inorganic substances, and known chemicals can be used. Examples of chemicals that decompose organic substances include sodium hypochlorite, hydrogen peroxide, sodium hydroxide, and ozone. These may be used individually or in combination of two or more types. When two or more chemicals that decompose organic substances are used in combination, the first chemical has a standard oxidation-reduction potential (25°C) measured using a hydrogen electrode preferably less than 2.0V, and the second chemical has a standard oxidation-reduction potential (25°C) measured using a hydrogen electrode preferably 2.0V or higher. Specifically, it is preferable to use sodium hypochlorite as the first chemical and ozone as the second chemical. As chemicals that decompose inorganic substances, examples of inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, or organic acids such as oxalic acid and citric acid can be used. These may also be used individually or in combination of two or more types. Furthermore, two or more chemical solutions that decompose organic matter and inorganic matter may be used in combination. When two or more chemical solutions that decompose organic matter and inorganic matter are used in combination, there is no particular limitation on which one is used as the first or second chemical solution. If the chemical solution that decomposes organic matter is used as the first chemical solution, the chemical solution that decomposes inorganic matter may be used as the second chemical solution, and if the chemical solution that decomposes inorganic matter is used as the first chemical solution, the chemical solution that decomposes organic matter may be used as the second chemical solution.

[0019] The concentrations of the chemical solutions in the first cleaning water 21 and the second cleaning water 26 are not particularly limited. However, when using a chemical solution that decomposes organic substances, the concentration of sodium hypochlorite (available chlorine concentration) is preferably 1.0 g / L or more and 5.0 g / L or less, and the concentration of sodium hydroxide is preferably 1.0 g / L or more and 4.0 g / L or less. For ozone, it is preferably 10 mg / L or more and 40 mg / L or less, more preferably 20 mg / L or more and 30 mg / L or less. When using a chemical solution that decomposes inorganic substances, the concentration of hydrochloric acid, sulfuric acid, or nitric acid is preferably 1.0 g / L or more and 10.0 g / L or less, the concentration of oxalic acid is preferably 1.0 g / L or more and 2.0 g / L or less, and the concentration of citric acid is preferably 1 g / L or more and 10 g / L or less. If the chemical solution concentration is lower than the above range, it takes time to decompose the contaminants attached to the filtration membrane, or the capacity of the cleaning water tank increases as the required amount of cleaning water increases. On the other hand, if the chemical solution concentration is higher than the above range, the consumption of the chemical solution increases, so the cost required for the chemical solution increases.

[0020] Although not shown in the figure, all pumps including the sludge extraction pump 9, the circulation pump 32, the membrane filtration pump 15, the first cleaning water pump 22, and the second cleaning water pump 27, all switching valves including the circulation switching valve 11, the air vent switching valve 33, the first switching valve 12, and the second switching valve 13, and all flow meters including the circulation flow meter 31, the membrane filtration water flow meter 16, the first cleaning water flow meter 23, and the second cleaning water flow meter 28 are connected to the controller 35, and the controller 35 controls all pumps and all switching valves.

[0021] When performing membrane filtration treatment on the water to be treated 1 using this water treatment system 100, the first side of the first switching valve 12 to the first wash water pipe 24 is closed, the side of the first switching valve 12 to the circulation switching valve 11 and the side to the membrane filtration tank 18 is opened, the second side of the second switching valve 13 to the second wash water pipe 29 is closed, the side of the second switching valve 13 to the circulation switching valve 11 and the side to the membrane filtration tank 18 is opened, the side of the circulation switching valve 11 to the wash water pipe 4, the side to the circulation pipe 30 and the side to the membrane filtration water pipe 14 are all opened, the side of the air vent switching valve 33 to the air vent switching valve 33 to the air vent switching valve 33 to the side to the second water collection port 37 and the side to the circulation switching valve 11 is opened, and the membrane filtration pump 15 is started, so that the water to be treated 1 is filtered by the filtration membrane of the filtration membrane module 3. The membrane filtration water filtered by the filtration membrane of the filtration membrane module 3 is discharged to the membrane filtration tank 18 through the membrane filtration water pipe 14. While the membrane filtration treatment of the water to be treated 1 is being performed, the blower 6 is constantly in operation. The sludge extraction pump 9 is operated according to the sludge concentration in the water tank to be treated 2, and the sludge is extracted from inside the water tank to be treated 2. If the membrane filtration treatment of the water to be treated 1 is continuously performed in the filtration membrane of the filtration membrane module 3, the filtration membrane of the filtration membrane module 3 will become clogged with pollutants, so it is necessary to clean the filtration membrane of the filtration membrane module 3.

[0022] The filtration membrane cleaning device of this water treatment system 100 can perform both dead-end filtration cleaning and cross-flow filtration cleaning in the cleaning process of the filtration membrane of the filtration membrane module 3. When dead-end filtration cleaning is selected as the cleaning of the filtration membrane of the filtration membrane module 3, first, stop the membrane filtration pump 15, close the side of the membrane filtration water tank 18 of the first switching valve 12, and close the side of the membrane filtration water tank 18 of the second switching valve 13. Next, open the side of the first cleaning water pipe 24 of the first switching valve 12, open the side of the circulation switching valve 11 of the first switching valve 12, open all of the side of the cleaning water pipe 4, the side of the circulation pipe 30, and the side of the membrane filtration water pipe 14 of the circulation switching valve 11, close the side of the air vent pipe 34 of the air vent switching valve 33, open the side of the second water collecting port 37 of the air vent switching valve 33 and the side of the circulation switching valve 11, and start the first cleaning water pump 22. Thus, the first cleaning water 21 from the first cleaning water tank 20 is supplied to the filtration membrane of the filtration membrane module 3 from both the first water collecting port 36 and the second water collecting port 37, and dead-end filtration cleaning is performed. After the dead-end filtration cleaning with the first cleaning water 21 is completed, stop the first cleaning water pump 22 and close the side of the first cleaning water pipe 24 of the first switching valve 12.

[0023] When subsequently performing dead-end filtration cleaning with the second cleaning water 26, open the side of the membrane filtration water tank 18 of the first switching valve 12, open the side of the second cleaning water pipe 29 of the second switching valve 13, open the side of the circulation switching valve 11 of the second switching valve 13, with all of the side of the cleaning water pipe 4, the side of the circulation pipe 30, and the side of the membrane filtration water pipe 14 of the circulation switching valve 11 being open, with the side of the air vent pipe 34 of the air vent switching valve 33 being closed, and with the side of the second water collecting port 37 of the air vent switching valve 33 and the side of the circulation switching valve 11 being open, start the second cleaning water pump 27. Thus, the second cleaning water 26 from the second cleaning water tank 25 is supplied to the filtration membrane of the filtration membrane module 3 from both the first water collecting port 36 and the second water collecting port 37, and dead-end filtration cleaning is performed. After the cleaning of the filtration membrane with the second cleaning water 26 is completed, stop the second cleaning water pump 27 and close the side of the second cleaning water pipe 29 of the second switching valve 13.

[0024] Once the cleaning of the filtration membrane by dead-end filtration cleaning is complete, the membrane filtration treatment of the water to be treated 1 is restarted by starting the membrane filtration pump 15, with the membrane filtration treatment of the water to be treated 1 restarted. This allows for continuous and efficient membrane filtration treatment of the water to be treated 1.

[0025] If cross-flow filtration cleaning is selected as the cleaning method for the filtration membrane of the filtration membrane module 3, first, the membrane filtration pump 15 is stopped, the membrane filtration tank 18 side of the first switching valve 12 is closed, the membrane filtration tank 18 side of the second switching valve 13 is closed, and the circulation piping 30 side of the circulation switching valve 11 is closed. Next, the first cleaning water piping 24 side of the first switching valve 12 is opened, the cleaning water piping 4 side and the membrane filtration water piping 14 side of the circulation switching valve 11 are opened, the second water collection port 37 side of the air vent switching valve 33, the circulation switching valve 11 side and the air vent piping 34 side are all opened, and the first cleaning water pump 22 is started, so that the first cleaning water 21 is supplied to the filtration membrane of the filtration membrane module 3 from the first water collection port 36. The first cleaning water 21 discharged from the second water collection port 37 passes through the circulation flow meter 31 and the air vent switching valve 33 and is discharged from the air vent piping 34. Then, when the flow rate of the cleaning water flowing through the circulation pipe 30, as measured by the circulation flow rate measuring device 31, exceeds a predetermined first membrane permeate flux, the first cleaning water pump 22 is stopped and the side of the first switching valve 12 connected to the first cleaning water pipe 24 is closed. Next, the side of the circulation switching valve 11 connected to the membrane filtration water pipe 14 is closed, the side of the circulation switching valve 11 connected to the circulation pipe 30 is opened, the side of the air vent switching valve 33 connected to the air vent pipe 34 is closed, and the circulation pump 32 is started, so that the first cleaning water 21 taken out from the second water collection port 37 is circulated through the circulation channel formed by the circulation pipe 30 and the cleaning water pipe 4 and supplied to the first water collection port 36, and cross-flow filtration cleaning is performed. The first wash water 21, which is used to clean the filtration membrane of the filtration membrane module 3 and taken out from the second water collection port 37, is not returned to the first wash water tank 20, but is circulated through the circulation channel formed by the circulation pipe 30 and the wash water pipe 4 and supplied to the first water collection port 36. Therefore, the first wash water 21 containing contaminants does not enter the first wash water tank 20. As a result, there is no need to clean the first wash water tank 20 after cleaning the filtration membrane, and it is only necessary to replenish the first wash water 21 used in the first wash water tank 20.

[0026] Due to the cross-flow filtration washing using the first wash water 21, the first wash water 21 permeates from the filtration membrane of the filtration membrane module 3 to the tank to be treated 2. As a result, the circulation flow rate of the first wash water 21 circulating in the circulation channel composed of the circulation piping 30 and the wash water piping 4 decreases, and the output value of the circulation flow meter 31 decreases. Therefore, when the value of the circulation flow rate obtained from the circulation flow meter 31 falls below a predetermined circulation flow threshold, the controller 35 stops the circulation pump 32, opens the side of the circulation switching valve 11 for the membrane filtration water piping 14, closes the side of the circulation switching valve 11 for the circulation piping 30, opens the side of the air vent switching valve 33 for the air vent piping 34, opens the side of the first switching valve 12 for the first wash water piping 24, and starts the first wash water pump 22 to supply the first wash water 21 from the first wash tank 20 to the circulation channel again. Then, when the value of the circulating flow rate obtained from the circulating flow rate meter 31 exceeds the circulating flow rate threshold, the first wash water pump 22 is stopped, the side of the first switching valve 12 connected to the first wash water piping 24 is closed, the side of the circulation switching valve 11 connected to the membrane filtration water piping 14 is closed, the side of the circulation switching valve 11 connected to the circulation piping 30 is opened, the side of the air vent switching valve 33 connected to the air vent piping 34 is closed, and the circulation pump 32 is restarted. This stops the supply of the first wash water 21 from the first wash water tank 20 to the circulation channel, and the first wash water 21 circulates through the circulation channel again. Through the above process, the flow rate of the wash water circulating through the circulation channel can be maintained in cross-flow filtration washing, and a decrease in washing efficiency due to the permeation of wash water from the filtration membrane to the treated water tank 2 can be prevented.

[0027] If cross-flow filtration cleaning is to be performed with the second wash water 26 after the completion of cross-flow filtration cleaning with the first wash water 21, first stop the circulation pump 32, open the side of the circulation switching valve 11 connected to the membrane filtration water piping 14, close the side of the circulation switching valve 11 connected to the circulation piping 30, and open the side of the air vent switching valve 33 connected to the air vent piping 34. Next, with the membrane filtration tank 18 side of the first switching valve 12 open, the second wash water piping 29 side of the second switching valve 13 open, the wash water piping 4 side of the circulation switching valve 11 open, the second water collection port 37 side and the circulation switching valve 11 side of the air vent switching valve 33 open, the first wash water piping 24 side of the first switching valve 12 closed, the circulation switching valve 11 side of the second switching valve 13 open, and the membrane filtration tank 18 side of the second switching valve 13 closed, the second wash water pump 27 is started, supplying the second wash water 26 from the first water collection port 36 to the filtration membrane of the filtration membrane module 3. Since the first wash water 21 used to wash the filtration membrane of the filtration membrane module 3 and taken out from the second water collection port 37 is not returned to the second wash water tank 25, the first wash water 21 remaining in the circulation path formed by the circulation piping 30 and the wash water piping 4 does not mix into the second wash water tank 25. Then, when the flow rate of the cleaning water flowing through the circulation pipe 30, as measured by the circulation flow rate meter 31, exceeds a predetermined second membrane permeate flux, the second cleaning water pump 27 is stopped and the second side of the second switching valve 13 to the second cleaning water pipe 29 is closed. As a result, the first cleaning water 21 remaining in the circulation channel and the filtration membrane module 3 is removed, and the circulation channel and the filtration membrane module 3 are filled with the second cleaning water 26, so that the filtration membrane is not cleaned by cleaning water that is a mixture of the first cleaning water 21 and the second cleaning water 26. For example, even if the first cleaning water 21 is alkaline and the second cleaning water 26 is acidic, the two cleaning waters will not mix and react, and the concentration of the cleaning water will not decrease during cleaning with the second cleaning water 26.Next, by closing the side of the circulation switching valve 11 connected to the membrane filtration water piping 14, opening the side of the circulation switching valve 11 connected to the circulation piping 30, closing the side of the air vent switching valve 33 connected to the air vent piping 34, and starting the circulation pump 32, the second wash water 26 taken out from the second water collection port 37 is circulated through the circulation channel formed by the circulation piping 30 and the wash water piping 4 and supplied to the first water collection port 36, thereby performing cross-flow filtration cleaning. The second wash water 26 used to clean the filtration membrane of the filtration membrane module 3 and taken out from the second water collection port 37 is not returned to the second wash water tank 25, but is circulated through the circulation channel formed by the circulation piping 30 and the wash water piping 4 and supplied to the first water collection port 36, so that the second wash water 26 containing contaminants does not enter the second wash water tank 25. Therefore, there is no need to clean the second wash water tank 25 after cleaning the filtration membrane, and it is only necessary to replenish the second wash water 26 used in the second wash water tank 25.

[0028] Due to the cross-flow filtration washing using the second wash water 26, the second wash water 26 permeates from the filtration membrane of the filtration membrane module 3 to the tank to be treated 2. As a result, the circulation flow rate of the second wash water 26 circulating in the circulation channel composed of the circulation piping 30 and the wash water piping 4 decreases, and the output value of the circulation flow meter 31 decreases. Therefore, when the value of the circulation flow rate obtained from the circulation flow meter 31 falls below a predetermined circulation flow threshold, the controller 35 stops the circulation pump 32, opens the side of the circulation switching valve 11 for the membrane filtration water piping 14, closes the side of the circulation switching valve 11 for the circulation piping 30, opens the side of the air vent switching valve 33 for the air vent piping 34, opens the side of the second switching valve 13 for the second wash water piping 29, and starts the second wash water pump 27 to supply the second wash water 26 from the second wash tank 25 to the circulation channel again. Then, when the value of the circulating flow rate obtained from the circulating flow rate meter 31 exceeds the circulating flow rate threshold, the second wash water pump 27 is stopped, the side of the second switching valve 13 connected to the second wash water piping 29 is closed, the side of the circulation switching valve 11 connected to the membrane filtration water piping 14 is closed, the side of the circulation switching valve 11 connected to the circulation piping 30 is opened, the side of the air vent switching valve 33 connected to the air vent piping 34 is closed, and the circulation pump 32 is restarted. This stops the supply of the second wash water 26 from the second wash water tank 25 to the circulation channel, and the second wash water 26 circulates through the circulation channel again. Through the above process, the flow rate of the wash water circulating through the circulation channel can be maintained in cross-flow filtration washing, and a decrease in washing efficiency due to the permeation of wash water from the filtration membrane to the treated water tank 2 can be prevented.

[0029] Once the cleaning of the filter membrane by cross-flow filtration is complete, the circulation pump 32 is stopped, the membrane filtration water piping 14 side of the circulation switching valve 11 is opened, the membrane filtration water tank 18 side of the second switching valve 13 is opened, the circulation switching valve 11 side of the second switching valve 13 is open, the circulation switching valve 11 side and the membrane filtration water tank 18 side of the first switching valve 12 are open, the cleaning water piping 4 side, the circulation piping 30 side and the membrane filtration water piping 14 side of the circulation switching valve 11 are all open, the air vent piping 34 side of the air vent switching valve 33 is closed, and the second water collection port 37 side and the circulation switching valve 11 side of the air vent switching valve 33 are open, and the membrane filtration treatment of the water to be treated 1 is restarted by starting the membrane filtration pump 15. This allows the membrane filtration treatment of the water to be treated 1 to be performed continuously and efficiently.

[0030] In the above description, an example was given in which dead-end filtration cleaning is performed with the second wash water 26 after the completion of dead-end filtration cleaning with the first wash water 21, or cross-flow filtration cleaning is performed with the second wash water 26 after the completion of cross-flow filtration cleaning with the first wash water 21. However, the controller 35 controls all pumps and all switching valves to perform one of the cleanings selected from dead-end filtration cleaning using the first wash water 21, cross-flow filtration cleaning using the first wash water 21, dead-end filtration cleaning using the second wash water 26, and cross-flow filtration cleaning using the second wash water 26. The order of the cleaning processes does not matter. Furthermore, in the water treatment system 100 equipped with the filtration membrane cleaning device according to Embodiment 1, an example using two types of washing water was shown, but the filtration membrane may be cleaned in the same manner using three or more types of washing water, or the filtration membrane may be cleaned using only the first wash water 21.

[0031] The washing time for the filtration membrane using washing water containing the chemical solution is not particularly limited and should be set appropriately depending on the amount of contaminants attached to the filtration membrane or the water collection method of the filtration membrane. Generally, it is preferable to wash for 90 minutes or less when using sodium hypochlorite, 60 minutes or less when using ozonated water, and 5 to 7 minutes when using oxalic acid or citric acid. Shorter washing times are preferable, as longer washing times result in longer interruptions in the membrane filtration treatment of the water to be treated, thus reducing the amount of water filtered through the membrane.

[0032] When cleaning the filtration membrane of the filtration membrane module 3 by dead-end filtration cleaning, the membrane permeation flux (amount of water supplied per unit area of ​​membrane) of the cleaning water containing the chemical solution is not particularly limited. Generally, it is sufficient to ensure a flux that can fill the end of the filtration membrane with cleaning water. Specifically, when using sodium hypochlorite, a flux of 6 LMH (L / m2 / h) or less is preferable, and when using ozonated water, a flux of 30 LMH (L / m2 / h) or less is preferable. If the membrane permeation flux is too high, the cost of the chemical solution will increase due to the increased amount of cleaning water required, the capacity of the cleaning water tank will increase, or the filtration membrane may rupture. If the membrane permeation flux is too low, the cleaning water will not fill the center of the filtration membrane, making it impossible to decompose contaminants attached to the filtration membrane, or, when using ozonated water, the concentration will decrease during transport.

[0033] Furthermore, when the filtration membrane of the filtration membrane module 3 is cleaned by cross-flow filtration, the circulation flow rate of the cleaning water containing the chemical solution is not particularly limited and may be the same as the membrane permeate flux of the cleaning water. The control method for the circulation pump 32 is such that the circulation flow rate of the cleaning water circulating in the circulation path formed by the circulation pipe 30 and the cleaning water pipe 4 is the same as the flow rate due to the membrane permeate flux. In this way, the output of the circulation pump may be increased when the circulation flow rate is less than the flow rate due to the membrane permeate flux, and the output of the circulation pump may be decreased when the circulation flow rate is greater than the flow rate due to the membrane permeate flux.

[0034] In the water treatment system 100 equipped with the filtration membrane cleaning device according to Embodiment 1, a cleaning method may be used in which cleaning water is passed through the filtration membrane and then the cleaning water is retained within the membrane, or a cleaning method may be used in which the filtration membrane is immersed in the cleaning solution and retained.

[0035] Although not shown in Figure 1, the washing water piping 4, the first washing water piping 24, the second washing water piping 29, or the circulation piping 30 may be equipped with means for uniformly mixing the first washing water 21 or the second washing water 26 (for example, a static mixer). Furthermore, pretreatment of the filtration membrane may be performed after the completion of the membrane filtration treatment but before the cleaning treatment of the filtration membrane. For example, by exposing the filtration membrane to air for a predetermined time after the completion of the membrane filtration treatment but before the cleaning treatment of the filtration membrane, it is possible to make it easier to remove contaminants adhering to the surface of the filtration membrane that is in contact with the water to be treated 1.

[0036] As described above, the filtration membrane cleaning device according to Embodiment 1 is a filtration membrane cleaning device for cleaning the filtration membrane of a filtration membrane module 3 equipped with two water collection ports, a first water collection port 36 and a second water collection port 37, for taking out membrane filtered water 19 that has permeated through the filtration membrane, and comprises: a first cleaning water piping 24 equipped with a first cleaning water pump 22 that supplies first cleaning water 21 from a first cleaning water tank 20; a membrane filtered water piping 14 connected to the first cleaning water piping 24 by a first switching valve 12; a cleaning water piping 4, one end of which is connected to the membrane filtered water piping 14 by a circulation switching valve 11 and the other end of which is connected to the first water collection port 36; a circulation piping 30, one end of which is connected to the membrane filtered water piping 14 and the cleaning water piping 4 by a circulation switching valve 11 and the other end of which is connected to the second water collection port 37, equipped with a circulation pump 32 that circulates the cleaning water; and the first cleaning water pump The system includes a controller 35 that controls the first washing water pump 22, the first switching valve 12, the circulation switching valve 11, and the circulation pump 32. The controller 35 controls the first washing water pump 22, the first switching valve 12, the circulation switching valve 11, and the circulation pump 32 to perform either dead-end filtration washing, which uses the first washing water 21 as washing water and the first washing water tank 20 as the washing water tank, and supplies washing water from the washing water tank to both the first collection port 36 and the second collection port 37, or cross-flow filtration washing, which circulates the washing water taken from the second collection port 37 through a circulation channel formed by the circulation piping 30 and the washing water piping 4 and supplies it to the first collection port 36. This allows for efficient removal of both contaminants adhering to the surface of the filtration membrane on the permeate channel side and contaminants adhering to the pores of the filtration membrane. Furthermore, since the cleaning method of the filtration membrane can be selected from dead-end filtration washing and cross-flow filtration washing, the appropriate cleaning method can be used according to the condition of the filtration membrane, resulting in high cleaning efficiency. Furthermore, in cross-flow filtration cleaning, the first cleaning water 21 used to clean the filtration membrane of the filtration membrane module 3 and taken out from the second water collection port 37 is not returned to the first cleaning tank 20, but is circulated through the circulation channel formed by the circulation pipe 30 and the cleaning water pipe 4 and supplied to the first water collection port 36. Therefore, the first cleaning water 21 containing contaminants does not enter the first cleaning tank 20. As a result, there is no need to clean the first cleaning tank 20 after cleaning the filtration membrane, and it is only necessary to replenish the first cleaning water 21 used in the first cleaning tank 20.

[0037] Furthermore, the filtration membrane cleaning apparatus according to Embodiment 1 includes a second cleaning water piping 29 equipped with a second cleaning water pump 27 that supplies second cleaning water 26 from a second cleaning water tank 25, the membrane filtration water piping 14 is connected to the second cleaning water piping 29 by a second switching valve 13, and the controller 35 uses the first cleaning water 21 as cleaning water and the first cleaning water tank 20 as the cleaning tank to perform either dead-end filtration cleaning or cross-flow filtration cleaning, and then uses the second cleaning water 26 as cleaning water and the second cleaning water tank 25 as the cleaning tank to perform dead-end filtration cleaning and cross-flow filtration cleaning. The first wash water pump 22, first switching valve 12, second wash water pump 27, second switching valve 13, circulation switching valve 11, and circulation pump 32 are controlled to perform one of the selected washes. As a result, the first wash water 21 used to wash the filter membrane of the filter membrane module 3 and taken out from the second water collection port 37 is not returned to the second wash water tank 25, and the first wash water 21 remaining in the circulation path formed by the circulation pipe 30 and wash water pipe 4 does not mix with the second wash water tank 25, thus preventing a decrease in the concentration of the second wash water 26 and a reduction in the washing effect.

[0038] Furthermore, in the first embodiment of the filtration membrane cleaning apparatus, the circulation piping 30 is equipped with a circulation flow rate measuring device 31 that measures the circulation flow rate, which is the flow rate of cleaning water flowing through the circulation piping 30. The controller 35 controls the supply of cleaning water from the cleaning tank to the circulation channel when the circulation flow rate is less than a predetermined circulation flow rate threshold in cross-flow filtration cleaning, and controls the supply of cleaning water from the cleaning tank to the circulation channel to stop when the circulation flow rate is equal to or greater than the circulation flow rate threshold. As a result, the flow rate of cleaning water circulating in the circulation channel can be maintained in cross-flow filtration cleaning, and a decrease in cleaning efficiency due to the permeation of cleaning water from the filtration membrane to the tank to be treated 2 can be prevented.

[0039] Although this application describes exemplary embodiments, the various features, aspects, and functions described in the embodiments are not limited to the application of any particular embodiment, but can be applied individually or in various combinations to the embodiments. Therefore, countless variations not exemplified are conceivable within the scope of the art disclosed herein. These include, for example, modifications, additions, or omissions of at least one component. [Explanation of Symbols]

[0040] 1. Water to be treated, 2. Water to be treated tank, 3. Filtration membrane module, 4. Wash water piping, 5. Water to be treated piping, 6. Blower, 7. Air piping, 8. Aeration device, 9. Sludge extraction pump, 10. Sludge extraction piping, 11. Circulation switching valve, 12. First switching valve, 13. Second switching valve, 14. Membrane filtered water piping, 15. Membrane filtration pump, 16. Membrane filtered water flow meter, 17. Membrane filtered water pressure gauge, 18. Membrane filtered water tank, 19. Membrane filtered water, 20. First washing tank, 21. First washing water, 22. First washing water pump, 23. First washing water flow meter, 24. First washing water piping, 25. Second washing tank, 26. Second washing water, 27. Second washing water pump, 28. Second washing water flow meter, 29. Second washing water piping, 30. Circulation piping, 31. Circulation flow meter, 32. Circulation pump, 33 Air vent switching valve, 34 Air vent piping, 35 Controller, 36 First water collection port, 37 Second water collection port, 100 Water treatment system.

Claims

1. A filtration membrane cleaning device for cleaning a filtration membrane of a filtration membrane module having two water collection ports, a first water collection port and a second water collection port, for extracting membrane filtrate that has permeated a filtration membrane, comprising: A controller is provided for controlling the cleaning of the filtration membrane based on a selection between dead-end filtration cleaning and cross-flow filtration cleaning, The controller includes: When the dead-end filtration cleaning is selected, control is performed to supply cleaning water to both the first water collection port and the second water collection port, A filtration membrane cleaning device characterized in that, when the cross-flow filtration cleaning is selected, control is performed so that the cleaning water is supplied to the first water collection port and discharged from the second water collection port.

2. A first cleaning water pipe equipped with a first cleaning water pump for supplying first cleaning water from a first cleaning water tank; A membrane filtrate water pipe connected to the first cleaning water pipe by a first switching valve; A cleaning water pipe having one end connected to the membrane filtrate water pipe by a circulation switching valve and the other end connected to the first water collection port; a circulation pipe having one end connected to the membrane filtered water pipe and the cleaning water pipe by the circulation switching valve and the other end connected to the second water collection port, the circulation pipe having a circulation pump for circulating the cleaning water; The controller includes: The first cleaning water is the cleaning water, and the first cleaning water tank is the cleaning water tank. When the dead-end filtration cleaning is selected, the first cleaning water pump, the first switching valve, the circulation switching valve, and the circulation pump are controlled so as to supply the cleaning water from the cleaning water tank to both the first water collection port and the second water collection port; The filtration membrane cleaning device described in claim 1, characterized in that when the cross-flow filtration cleaning is selected, the first cleaning water pump, the first switching valve, the circulation switching valve and the circulation pump are controlled so that the cleaning water taken out from the second water collection port is circulated through a circulation flow path formed by the circulation piping and the cleaning water piping and supplied to the first water collection port.

3. a second cleaning water piping having a second cleaning water pump for supplying second cleaning water from the second cleaning water tank; The membrane filtrate water pipe is connected to the second cleaning water pipe by a second switching valve, The filtration membrane cleaning device of claim 2, characterized in that the controller controls the first cleaning water pump, the first switching valve, the second cleaning water pump, the second switching valve, the circulation switching valve and the circulation pump so as to perform one of the cleanings selected from the dead-end filtration cleaning and the cross-flow filtration cleaning, using the first cleaning water as the cleaning water and the first cleaning water tank as the cleaning water tank, and then perform one of the cleanings selected from the dead-end filtration cleaning and the cross-flow filtration cleaning, using the second cleaning water as the cleaning water and the second cleaning water tank as the cleaning water tank.

4. The circulation pipe is provided with a circulation flow rate measuring device that measures a circulation flow rate, which is a flow rate of the cleaning water flowing through the circulation pipe, The filtration membrane cleaning device according to claim 2 or 3, characterized in that, in the cross-flow filtration cleaning, the controller controls the cleaning water to be supplied from the cleaning water tank to the circulation flow path when the circulation flow rate is less than a predetermined circulation flow rate threshold, and controls the supply of the cleaning water from the cleaning water tank to the circulation flow path to be stopped when the circulation flow rate is equal to or greater than the circulation flow rate threshold.

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