WO2024154319A1 - Filtration membrane cleaning device - Google Patents

Abstract

Provided is a filtration membrane cleaning device that efficiently removes both a contaminant adhering to the surface of a filtration membrane on a permeate passage side thereof and a contaminant adhering in pores of the filtration membrane.　The present invention is a filtration membrane cleaning device that cleans a filtration membrane of a filtration membrane module (3) provided with a first water collecting port (36) and a second water collecting port (37) that extract membrane-filtered water (19) that has passed through the filtration membrane, the filtration membrane cleaning device comprising 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) so as to perform either cleaning selected from dead-end filtration cleaning in which first cleaning water (21) is used as cleaning water, a first cleaning water tank (20) is used as a cleaning water tank, and cleaning water from the cleaning water tank is supplied to both the first water collecting port (26) and the second water collecting port (37), and crossflow filtration cleaning in which cleaning water extracted from the second water collecting port (37) is circulated through a circulation passage constituted from a circulation pipe (30) and a cleaning water pipe (4) and supplied to the first water collection port (36).

Description

Filtration membrane cleaning equipment

This application relates to a filter membrane cleaning device.

Membrane filtration is used as a method for separating suspended solids from water to be treated. For example, in the treatment of sewage or industrial wastewater, after the water to be treated is treated by the activated sludge process, suspended solids are separated and removed using a membrane filter. Generally, cylindrical or sheet-shaped microfiltration or ultrafiltration membranes are used as the membrane filter. Filtration methods include external pressure filtration, in which the water to be treated flows on the outside of a cylindrical or sheet-shaped membrane filter and the filtered water flows on the inside, and internal pressure filtration, in which the water to be treated flows on the inside of a cylindrical membrane filter and the filtered water flows on the outside. In addition, methods for collecting filtered water include one-end collection, in which water is collected from one collection port of the membrane filter, and both-end collection, in which water is collected from two collection ports of the membrane filter.

Membrane filtration processes using such membranes have the problem that the filtration performance declines with continued use of the membrane. Specifically, with continued use of the membrane, contaminants adhere to the membrane surface that comes into contact with the water to be treated (the outer surface of the membrane in the external pressure filtration method, and the inner surface of the membrane in the internal pressure filtration method), the membrane surface that comes into contact with the filtrate (the inner surface of the membrane in the external pressure filtration method, and the outer surface of the membrane in the internal pressure filtration method), or the pores of the membrane, causing clogging and gradually decreasing the filtration performance. In particular, when the membrane becomes clogged, the pressure required for filtration increases, and the membrane filtration flux (the amount of water filtered through the membrane per unit membrane area per unit time) also decreases. Therefore, in order to maintain the performance of the membrane, it is necessary to periodically clean the membrane.

As a method for maintaining the filtration performance, backflow washing is performed to physically remove contaminants attached to the surface of the filtration membrane in contact with the water to be treated by passing washing water such as membrane filtrate or clear water through the filtration membrane from the secondary side opposite to the primary side of the filtration membrane. In addition, in order to further enhance the cleaning effect of the filtration membrane, a method has been proposed in which backflow washing of the filtration membrane is performed using washing water containing an oxidizing agent such as sodium hypochlorite (also called "soda hypochlorite") or ozone, thereby oxidizing and decomposing contaminants chemically attached to the surface of the filtration membrane in contact with the membrane filtrate or in the pores of the filtration membrane by intermolecular forces, etc. In addition, when washing water such as membrane filtrate or clear water is passed through the filtration membrane from the secondary side opposite to the primary side of the filtration membrane, the method of passing the washing water differs depending on the method of collecting the filtrate mentioned above. For filtration membranes that collect water at one end, washing is performed by dead-end filtration (full-volume filtration), in which washing water is supplied from one water collection port of the filtration membrane. For filtration membranes that collect water at both ends, cleaning is performed by dead-end filtration, in which cleaning water is supplied from two water collection ports of the filtration membrane, or by cross-flow filtration (parallel filtration), in which cleaning water is supplied from one water collection port of the filtration membrane and discharged from the other water collection port. For example, in cross-flow filtration, a cleaning method has been proposed in which the amount of cleaning water supplied is increased or decreased to repeatedly expand and contract the filtration membrane, thereby peeling off contaminants attached to the surface of the filtration membrane (see, for example, Patent Document 1).

Patent No. 5473897

In the filtration membrane cleaning device shown in Patent Document 1, cleaning is performed by cross-flow filtration of cleaning water, and because the cleaning water continues to flow through the permeate flow path of the filtration membrane, the cleaning water is spread evenly over the entire filtration membrane, effectively removing contaminants adhering to the surface of the permeate flow path side of the filtration membrane. However, because only a portion of the cleaning water permeates to the primary side of the filtration membrane, there is an issue that the efficiency of removing contaminants adhering to the pores of the filtration membrane is low compared to cleaning by dead-end filtration, in which the entire amount of cleaning water permeates to the primary side of the filtration membrane.

The present application has been made to solve the above-mentioned problems, and aims to provide a filtration membrane cleaning device that efficiently removes both contaminants adhering to the surface of the filtration membrane on the permeate flow path side and contaminants adhering to the pores of the filtration membrane.

The filtration membrane cleaning device disclosed in the present application is a filtration membrane cleaning device for cleaning the filtration membrane of a filtration membrane module having two collection ports, a first collection port and a second collection port, for extracting membrane filtrate that has permeated the filtration membrane, and includes a first cleaning water piping having a first cleaning water pump for supplying first cleaning water from a first cleaning water tank, a membrane filtrate water piping connected to the first cleaning water piping by a first switching valve, a cleaning water piping having one end connected to the membrane filtrate water piping by a circulation switching valve and the other end connected to the first collection port, and a cleaning water piping having one end connected to the membrane filtrate water piping and the cleaning water piping by a circulation switching valve and the other end connected to the second collection port, which circulates the cleaning water. The system includes a circulation pipe having a circulation pump, and a controller for controlling the first cleaning water pump, the first switching valve, the circulation switching valve, and the circulation pump. The controller controls the first cleaning water pump, the first switching valve, the circulation switching valve, and the circulation pump to perform one of two cleaning methods selected from dead-end filtration cleaning, in which the first cleaning water is used as the cleaning water and the first cleaning water tank is used as the cleaning water tank, and cleaning water from the cleaning water tank is supplied to both the first water collection port and the second water collection port, and cross-flow filtration cleaning, in which cleaning water taken out from the second water collection port is circulated through a circulation flow path formed by the circulation pipe and the cleaning water pipe and supplied to the first water collection port.

The filtration membrane cleaning device disclosed in the present application is a filtration membrane cleaning device for cleaning the filtration membrane of a filtration membrane module having two collection ports, a first collection port and a second collection port, for extracting membrane filtrate that has permeated the filtration membrane, and includes a first cleaning water piping having a first cleaning water pump that supplies first cleaning water from a first cleaning water tank, a membrane filtrate water piping connected to the first cleaning water piping by a first switching valve, a cleaning water piping having one end connected to the membrane filtrate water piping by a circulation switching valve and the other end connected to the first collection port, a circulation piping having one end connected to the membrane filtrate water piping and the cleaning water piping by the circulation switching valve and the other end connected to the second collection port, and having a circulation pump that circulates the cleaning water, and the first cleaning water pump, the first switching valve, , and a controller that controls the circulation switching valve and the circulation pump. The controller controls the first washing water pump, the first switching valve, the circulation switching valve and the circulation pump to perform one of two types of washing selected from dead-end filtration washing, in which the first washing water is used as the washing water and the first washing water tank is used as the washing water tank, and the washing water from the washing water tank is supplied to both the first water collection port and the second water collection port, and cross-flow filtration washing, in which the washing water taken out from the second water collection port is circulated through a circulation flow path formed by the circulation piping and the washing water piping and supplied to the first water collection port, thereby efficiently removing both contaminants attached to the surface of the filtration membrane on the permeate flow path side and contaminants attached in the pores of the filtration membrane.

1 is a diagram showing a configuration of a water treatment system including a filtration membrane cleaning device according to a first embodiment.

Below, a filtration membrane cleaning device according to an embodiment for carrying out the present application will be described in detail with reference to the drawings. Note that the same reference numerals in each drawing indicate the same or corresponding parts.

Embodiment 1.
1 is a diagram showing the configuration of a water treatment system 100 including a filtration membrane cleaning device according to embodiment 1. The water treatment system 100 includes a treated water tank 2 that contains treated water 1, a filtration membrane module 3 that performs membrane filtration treatment on the treated water 1, a membrane filtration water tank 18 that contains membrane filtered water 19, and a filtration membrane cleaning device.

The treated water tank 2 is provided with a treated water pipe 5 for supplying the treated water 1, and in the treated water tank 2, the treated water 1 is subjected to membrane filtration treatment by a filtration membrane module 3. The treated water 1 is, for example, water supply, sewerage, secondary sewage treatment water, industrial wastewater, seawater, or human waste. A sludge extraction pipe 10 and an air pipe 7 are connected to the treated water tank 2, and an aeration device 8 is disposed at the bottom of the treated water tank 2. A blower 6 is connected to the aeration device 8 via the air pipe 7, and is used to air wash 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.

The filtration membrane module 3 is equipped with a filtration membrane and two water collection ports, a first water collection port 36 and a second water collection port 37, which are used to extract the membrane filtrate that has permeated 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 may be any material that is not deteriorated 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-perfluoroalkylvinyl 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 ethyl cellulose, and ceramics. The material of the filtration membrane of the filtration membrane module 3 may also be a combination of two or more of the above substances. The material of the filtration membrane of the filtration membrane module 3 is preferably a fluorine-based resin compound that has excellent resistance to strong oxidizing agents such as ozone.

The type of the filtration membrane of 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 of the filtration membrane module 3 is not particularly limited, and 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 the pollutants attached to the surface of the filtration membrane in contact with the water to be treated 1, but also the pollutants chemically attached to the surface of the filtration membrane in contact with the membrane filtrate 19 and in the pores of the filtration membrane. The shape of the filtration membrane of the filtration membrane module 3 is not particularly limited, and may be a known shape such as a cylindrical shape or a flat membrane shape. The filtration membrane of the filtration membrane module 3 may be an immersion type, a casing type, or a 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 of 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 membrane 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 membrane filtered water 19 flows outside the filtration membrane. The water collection method of the filtration membrane module 3 is a double-end water collection method in which water is collected from two water collection ports, the first water collection port 36 and the second water collection port 37.

The cleaning water pipe 4 is connected at one end to the membrane filtered water pipe 14 by the circulation switching valve 11, and at the other end to the first water collection port 36. The circulation pipe 30 is connected at one end to the membrane filtered water pipe 14 and the cleaning water pipe 4 by the circulation switching valve 11, and at the other end to the second water collection port 37, and is equipped with a circulation pump 32 that circulates the cleaning water, a circulation flow rate meter 31 that measures the flow rate of the circulated cleaning water, and an air vent switching valve 33. The air vent switching valve 33 is connected to the air vent pipe 34. The membrane filtered water pipe 14 is connected at one end to the cleaning water pipe 4 and the circulation pipe 30 by the circulation switching valve 11, and at the other end to the membrane filtered water tank 18 that contains the membrane filtered water 19, and is equipped with a membrane filtered water pump 15, a membrane filtered water flow rate meter 16, and a membrane filtered water pressure gauge 17.

The first cleaning water pipe 24 has one end connected to the membrane filtrate water pipe 14 by the first switching valve 12, and the other end connected to the first cleaning water tank 20. The first cleaning water pipe 24 is equipped with a first cleaning water pump 22 for supplying the first cleaning water 21 contained in the first cleaning water tank 20 to the filtration membrane of the filtration membrane module 3, and a first cleaning water flow rate meter 23 for measuring the flow rate of the first cleaning water 21. The second cleaning water pipe 29 is also equipped with one end connected to the membrane filtrate water pipe 14 by the second switching valve 13, and the other end connected to the second cleaning water tank 25. The second cleaning water pipe 29 is equipped with a second cleaning water pump 27 for supplying the second cleaning water 26 contained in the second cleaning water tank 25 to the filtration membrane of the filtration membrane module 3, and a second cleaning water flow rate meter 28 for measuring the flow rate of the second cleaning water 26.

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

The concentrations of the chemicals in the first cleaning water 21 and the second cleaning water 26 are not particularly limited, but when a chemical that decomposes organic matter is used, it is preferable that sodium hypochlorite (effective chlorine concentration) is 1.0 g/L or more and 5.0 g/L or less, and that sodium hydroxide is 1.0 g/L or more and 4.0 g/L or less. For ozone, it is preferable that it is 10 mg/L or more and 40 mg/L or less, and more preferably 20 mg/L or more and 30 mg/L or less. When a chemical that decomposes inorganic matter is used, it is preferable that hydrochloric acid, sulfuric acid, and nitric acid are 1.0 g/L or more and 10.0 g/L or less, oxalic acid is 1.0 g/L or more and 2.0 g/L or less, and citric acid is 1 g/L or more and 10 g/L or less. If the chemical concentration is lower than the above range, it will take time to decompose the pollutants attached to the filtration membrane, and the capacity of the cleaning water tank will increase as the required amount of cleaning water increases. On the other hand, if the chemical concentration is higher than the above range, the amount of chemical consumed will increase, and the cost of the chemical will increase.

Although not shown, all of the pumps, 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 of the switching valves, the circulation switching valve 11, the air vent switching valve 33, the first switching valve 12 and the second switching valve 13, and all of the flow meters, 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 a controller 35, which controls all of the pumps and all of the switching valves.

When the water treatment system 100 performs membrane filtration of the water to be treated 1, the first switching valve 12 is closed on the first cleaning water pipe 24 side, the first switching valve 12 is opened on the circulation switching valve 11 side and the membrane filtration water tank 18 side, the second switching valve 13 is closed on the second cleaning water pipe 29 side, the second switching valve 13 is opened on the circulation switching valve 11 side and the membrane filtration water tank 18 side, the cleaning water pipe 4 side, the circulation pipe 30 side and the membrane filtration water pipe 14 side of the circulation switching valve 11 are all opened, the air vent pipe 34 side of the air vent switching valve 33 is closed, the second water collection port 37 side and the circulation switching valve 11 side of the air vent switching valve 33 are opened, and the membrane filtration pump 15 is started, whereby 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 through the membrane filtration water pipe 14 to the membrane filtration water tank 18. The blower 6 is always running while the membrane filtration process of the water to be treated 1 is being performed. The sludge extraction pump 9 is operated according to the sludge concentration in the water to be treated tank 2, and the sludge inside the water to be treated tank 2 is extracted. If the membrane filtration process of the water to be treated 1 is continuously performed using the filtration membrane of the filtration membrane module 3, the filtration membrane of the filtration membrane module 3 will become clogged with pollutants, and therefore the filtration membrane of the filtration membrane module 3 needs to be cleaned.

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 for cleaning the filtration membrane of the filtration membrane module 3, first, the membrane filtration pump 15 is stopped, the side of the first switching valve 12 facing the membrane filtration water tank 18 is closed, and the side of the second switching valve 13 facing the membrane filtration water tank 18 is closed. Next, the first switching valve 12 is opened on the first cleaning water pipe 24 side, the first switching valve 12 is opened on the circulation switching valve 11 side, the cleaning water pipe 4 side, the circulation pipe 30 side, and the membrane filtrate water pipe 14 side of the circulation switching valve 11 are all opened, the air vent pipe 34 side of the air vent switching valve 33 is closed, the second water collection port 37 side of the air vent switching valve 33 and the circulation switching valve 11 side are opened, and the first cleaning water pump 22 is started, so that the first cleaning water 21 is supplied from the first cleaning water tank 20 to the filtration membrane of the filtration membrane module 3 from both the first water collection port 36 and the second water collection port 37, and dead-end filtration cleaning is performed. After the dead-end filtration cleaning with the first cleaning water 21 is completed, the first cleaning water pump 22 is stopped, and the first switching valve 12 is closed on the first cleaning water pipe 24 side.

　To perform dead-end filtration cleaning using the second cleaning water 26, the first switching valve 12 is opened on the membrane filtration water tank 18 side, the second switching valve 13 is opened on the second cleaning water pipe 29 side, the second switching valve 13 is opened on the circulation switching valve 11 side, the cleaning water pipe 4 side, the circulation pipe 30 side, and the membrane filtration water pipe 14 side of the circulation switching valve 11 are all open, the air vent pipe 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 opened. In this state, the second cleaning water pump 27 is started, and 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 collection port 36 and the second water collection port 37, thereby performing dead-end filtration cleaning. After the cleaning of the filtration membrane with the second cleaning water 26 is completed, the second cleaning water pump 27 is stopped, and the second switching valve 13 is closed on the second cleaning water pipe 29 side.

When the cleaning of the filtration membrane by dead-end filtration cleaning is completed, the membrane filtration process of the treated water 1 is resumed by opening the membrane filtration tank 18 side of the second switching valve 13, opening the circulation switching valve 11 side of the second switching valve 13, opening the circulation switching valve 11 side and the membrane filtration tank 18 side of the first switching valve 12, opening the cleaning water pipe 4 side, the circulation pipe 30 side and the membrane filtration water pipe 14 side of the circulation switching valve 11, closing the air vent pipe 34 side of the air vent switching valve 33, and opening the second water collection port 37 side and the circulation switching valve 11 side of the air vent switching valve 33. This allows the membrane filtration process of the treated water 1 to be performed continuously and efficiently.

When cross-flow filtration cleaning is selected as the cleaning of the filtration membrane of the filtration membrane module 3, first, the membrane filtration pump 15 is stopped, the membrane filtration water tank 18 side of the first switching valve 12 is closed, the membrane filtration water 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, and the second water collection port 37 side, the circulation switching valve 11 side, and the air vent piping 34 side of the air vent switching valve 33 are all opened, and the first cleaning water pump 22 is started, whereby the first cleaning water 21 is supplied from the first water collection port 36 to the filtration membrane of the filtration membrane module 3. The first cleaning water 21 discharged from the second water collection port 37 passes through the circulation flow rate measuring device 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 piping 30 measured by the circulation flow rate measuring device 31 exceeds a predetermined first membrane surface permeation flux, the first cleaning water pump 22 is stopped and the first cleaning water piping 24 side of the first switching valve 12 is closed. Next, the membrane filtrate water piping 14 side of the circulation switching valve 11 is closed, the circulation piping 30 side of the circulation switching valve 11 is opened, the air vent piping 34 side of the air vent switching valve 33 is closed, and the circulation pump 32 is started, whereby the first cleaning water 21 taken out from the second water collection port 37 is circulated through the circulation flow path formed by the circulation piping 30 and the cleaning water piping 4 and supplied to the first water collection port 36, and cross-flow filtration cleaning is performed. 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 water tank 20, but is circulated through a circulation flow path formed by the circulation piping 30 and the cleaning water piping 4 and supplied to the first water collection port 36, so that the first cleaning water 21 containing contaminants does not enter the first cleaning water tank 20. Therefore, it is not necessary to clean the first cleaning water tank 20 after cleaning the filtration membrane, and it is only necessary to refill the first cleaning water tank 20 with the amount of first cleaning water 21 used.

By cross-flow filtration cleaning using the first cleaning water 21, the first cleaning water 21 permeates through the filtration membrane of the filtration membrane module 3 into the treated water tank 2, so that the circulation flow rate of the first cleaning water 21 circulating through the circulation flow path formed by the circulation piping 30 and the cleaning water piping 4 decreases, and the output value of the circulation flow rate meter 31 decreases. Therefore, when the value of the circulation flow rate obtained from the circulation flow rate meter 31 becomes less than a predetermined circulation flow rate threshold, the controller 35 stops the circulation pump 32, opens the membrane filtrate water piping 14 side of the circulation switching valve 11, closes the circulation piping 30 side of the circulation switching valve 11, opens the air vent piping 34 side of the air vent switching valve 33, opens the first cleaning water piping 24 side of the first switching valve 12, and starts the first cleaning water pump 22, thereby supplying the first cleaning water 21 from the first cleaning water tank 20 to the circulation flow path again. Then, when the value of the circulation flow rate acquired from the circulation flow rate measuring device 31 becomes equal to or greater than the circulation flow rate threshold value, the first cleaning water pump 22 is stopped, the first switching valve 12 is closed on the side of the first cleaning water pipe 24, the circulation switching valve 11 is closed on the side of the membrane filtrate water pipe 14, the circulation switching valve 11 is opened on the side of the circulation pipe 30, the air vent switching valve 33 is closed on the side of the air vent pipe 34, and the circulation pump 32 is started again, thereby stopping the supply of the first cleaning water 21 from the first cleaning water tank 20 to the circulation flow path, and the first cleaning water 21 circulates through the circulation flow path again. By the above process, the flow rate of the cleaning water circulating through the circulation flow path in the cross-flow filtration cleaning can be maintained, and a decrease in cleaning efficiency due to the permeation of the cleaning water from the filtration membrane to the treated water tank 2 can be prevented.

When performing cross-flow filtration cleaning with the second cleaning water 26 after completion of cross-flow filtration cleaning with the first cleaning water 21, first stop the circulation pump 32, open the membrane filtrate water piping 14 side of the circulation switching valve 11, close the circulation piping 30 side of the circulation switching valve 11, and open the air vent piping 34 side of the air vent switching valve 33. Next, in a state where the first switching valve 12 is opened on the membrane filtration water tank 18 side, the second switching valve 13 is opened on the second cleaning water pipe 29 side, the circulation switching valve 11 is opened on the cleaning water pipe 4 side, the second water collection port 37 side and the circulation switching valve 11 side of the air vent switching valve 33 are opened, the first cleaning water pipe 24 side of the first switching valve 12 is closed, the circulation switching valve 11 side of the second switching valve 13 is opened, and the membrane filtration water tank 18 side of the second switching valve 13 is closed, the second cleaning water pump 27 is started, and the second cleaning water 26 is supplied from the first water collection port 36 to the filtration membrane of the filtration membrane module 3. Since the first cleaning water 21 used for cleaning 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 cleaning water tank 25, the first cleaning water 21 remaining in the circulation flow path formed by the circulation pipe 30 and the cleaning water pipe 4 is not mixed into the second cleaning water tank 25. Then, when the flow rate of the cleaning water flowing through the circulation piping 30 measured by the circulation flow rate measuring device 31 exceeds a predetermined second membrane surface permeation flux, the second cleaning water pump 27 is stopped and the second switching valve 13 is closed on the side of the second cleaning water piping 29. As a result, the first cleaning water 21 remaining in the circulation flow path and the filtration membrane module 3 is removed, and the circulation flow path and the filtration membrane module 3 are filled with the second cleaning water 26, and the filtration membrane is not washed with the 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 do not mix and react with each other, and the concentration of the cleaning water does not decrease in washing with the second cleaning water 26. Next, the membrane filtrate water pipe 14 side of the circulation switching valve 11 is closed, the circulation pipe 30 side of the circulation switching valve 11 is opened, the air vent pipe 34 side of the air vent switching valve 33 is closed, and the circulation pump 32 is started, so that the second cleaning water 26 taken out from the second water collection port 37 is circulated through the circulation flow path 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 second cleaning water 26 used for cleaning 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 cleaning water tank 25, but is circulated through the circulation flow path formed by the circulation pipe 30 and the cleaning water pipe 4 and supplied to the first water collection port 36, so that the second cleaning water 26 containing contaminants does not enter the second cleaning water tank 25. Therefore, there is no need to clean the second cleaning water tank 25 after cleaning the filtration membrane, and it is only necessary to refill the second cleaning water tank 25 with the second cleaning water 26 used.

By cross-flow filtration cleaning using the second cleaning water 26, the second cleaning water 26 permeates through the filtration membrane of the filtration membrane module 3 into the treated water tank 2, so that the circulation flow rate of the second cleaning water 26 circulating through the circulation flow path formed by the circulation piping 30 and the cleaning water piping 4 decreases, and the output value of the circulation flow rate meter 31 decreases. Therefore, when the value of the circulation flow rate obtained from the circulation flow rate meter 31 becomes less than a predetermined circulation flow rate threshold, the controller 35 stops the circulation pump 32, opens the membrane filtrate water piping 14 side of the circulation switching valve 11, closes the circulation piping 30 side of the circulation switching valve 11, opens the air vent piping 34 side of the air vent switching valve 33, opens the second cleaning water piping 29 side of the second switching valve 13, and starts the second cleaning water pump 27, thereby again supplying the second cleaning water 26 from the second cleaning water tank 25 to the circulation flow path. Then, when the value of the circulation flow rate acquired from the circulation flow rate measuring device 31 becomes equal to or greater than the circulation flow rate threshold value, the second cleaning water pump 27 is stopped, the second switching valve 13 is closed on the side of the second cleaning water pipe 29, the circulation switching valve 11 is closed on the side of the membrane filtrate water pipe 14, the circulation switching valve 11 is opened on the side of the circulation pipe 30, the air vent switching valve 33 is closed on the side of the air vent pipe 34, and the circulation pump 32 is started again, thereby stopping the supply of the second cleaning water 26 from the second cleaning water tank 25 to the circulation flow path, and the second cleaning water 26 circulates through the circulation flow path again. By the above process, the flow rate of the cleaning water circulating through the circulation flow path in the cross-flow filtration cleaning can be maintained, and a decrease in cleaning efficiency due to the permeation of the cleaning water from the filtration membrane to the treated water tank 2 can be prevented.

When the cleaning of the filtration membrane by cross-flow filtration cleaning is completed, the circulation pump 32 is stopped, the membrane filtration water pipe 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 and the membrane filtration water tank 18 side of the first switching valve 12 are opened, the cleaning water pipe 4 side, the circulation pipe 30 side and the membrane filtration water pipe 14 side of the circulation switching valve 11 are all open, the air vent pipe 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 are opened. Then, the membrane filtration pump 15 is started to resume the membrane filtration process of the water to be treated 1. This allows the membrane filtration process of the water to be treated 1 to be performed continuously and efficiently.

In the above description, an example was described in which dead-end filtration cleaning with the second cleaning water 26 is performed after completion of dead-end filtration cleaning with the first cleaning water 21, or cross-flow filtration cleaning with the second cleaning water 26 is performed after completion of cross-flow filtration cleaning with the first cleaning water 21. However, the controller 35 controls all pumps and all switching valves to perform any one of dead-end filtration cleaning using the first cleaning water 21 as the cleaning water, cross-flow filtration cleaning using the first cleaning water 21 as the cleaning water, dead-end filtration cleaning using the second cleaning water 26 as the cleaning water, and cross-flow filtration cleaning using the second cleaning water 26 as the cleaning water, and the order of the cleaning processes may be any order. Furthermore, in the water treatment system 100 equipped with the filtration membrane cleaning device according to embodiment 1, an example was shown in which two types of cleaning water were used, but the filtration membrane may be cleaned by the same method using three or more types of cleaning water, or the filtration membrane may be cleaned using only the first cleaning water 21.

The cleaning time for the filtration membrane using cleaning water containing a chemical solution is not particularly limited, and may be set appropriately depending on the amount of contaminants attached to the filtration membrane or the water collection method of the filtration membrane. In general, 90 minutes or less is preferred when using sodium hypochlorite, 60 minutes or less when using ozone water, and 5 to 7 minutes is preferred when using oxalic acid or citric acid. A shorter cleaning time is preferred, and if the cleaning time is longer, the amount of membrane filtered water will decrease because the time for which the membrane filtration process of the treated water is interrupted will also be longer.

When the cleaning of the filtration membrane of the filtration membrane module 3 is performed by dead-end filtration cleaning, the membrane surface permeation flux (amount of water supplied per membrane area) of the cleaning water containing the chemical solution is not particularly limited. In general, it is sufficient to ensure a flux that can fill the cleaning water to the end of the filtration membrane. Specifically, when sodium hypochlorite is used, it is preferable to use a flux of 6 LMH (L/m2/h) or less, and when ozone water is used, it is preferable to use a flux of 30 LMH (L/m2/h) or less. If the membrane surface permeation flux is too high, the cost of the chemical solution increases due to the increase in the required amount of cleaning water, the capacity of the cleaning water tank increases, or the filtration membrane breaks. If the membrane surface permeation flux is too low, the cleaning water does not fill up to the center of the filtration membrane, making it impossible to decompose the pollutants attached to the filtration membrane, or when ozone water is used, the concentration decreases during transportation.

In addition, when the cleaning of the filtration membrane of the filtration membrane module 3 is performed by cross-flow filtration cleaning, the circulation flow rate of the cleaning water containing the chemical solution is not particularly limited and may be the same as the membrane surface permeation flux of the cleaning water. The method of controlling the circulation pump 32 may be to increase the output of the circulation pump when the circulation flow rate is less than the membrane surface permeation flux so that the circulation flow rate of the cleaning water circulating through the circulation flow path formed by the circulation piping 30 and the cleaning water piping 4 is the same as the flow rate due to the membrane surface permeation flux, or to decrease the output of the circulation pump when the circulation flow rate is greater than the flow rate due to the membrane surface permeation flux.

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 retained within the membrane, or a cleaning method may be used in which the filtration membrane is immersed in and retained in a cleaning solution.

Although not shown in FIG. 1, the cleaning water pipe 4, the first cleaning water pipe 24, the second cleaning water pipe 29, or the circulation pipe 30 may be provided with a means for uniformly mixing the first cleaning water 21 or the second cleaning water 26 (e.g., a static mixer). In addition, after the membrane filtration process is completed and before the cleaning process of the filtration membrane is performed, a preliminary treatment of the filtration membrane may be performed. For example, after the membrane filtration process is completed and before the cleaning process of the filtration membrane is performed, the filtration membrane may be exposed to air for a predetermined time, which makes it easier to remove contaminants attached to the surface of the filtration membrane that comes into contact with the water to be treated 1.

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, which has two water collection ports, the first water collection port 36 and the second water collection port 37, for extracting the membrane filtrate 19 that has permeated the filtration membrane, and includes a first cleaning water piping 24 equipped with a first cleaning water pump 22 that supplies the first cleaning water 21 from the first cleaning water tank 20, a membrane filtrate piping 14 connected to the first cleaning water piping 24 by a first switching valve 12, a cleaning water piping 4 having one end connected to the membrane filtrate piping 14 by a circulation switching valve 11 and the other end connected to the first water collection port 36, a circulation piping 30 having one end connected to the membrane filtrate piping 14 and the cleaning water piping 4 by the circulation switching valve 11 and the other end connected to the second water collection port 37, and equipped with a circulation pump 32 that circulates the cleaning water, and a first cleaning water pump 22 that supplies the first cleaning water 21 from the first cleaning water tank 20. 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 of dead-end filtration washing, in which the first washing water 21 is used as the washing water and the first washing water tank 20 is used as the washing water tank, and the washing water from the washing water tank is supplied to both the first water collection port 36 and the second water collection port 37, or cross-flow filtration washing, in which the washing water taken out from the second water collection port 37 is circulated through a circulation flow path formed by the circulation piping 30 and the washing water piping 4 and supplied to the first water collection port 36. This makes it possible to efficiently remove both contaminants attached to the surface of the filtration membrane on the permeate flow path side and contaminants attached in the pores of the filtration membrane. In addition, the method for washing the filtration membrane can be selected from dead-end filtration washing and cross-flow filtration washing, so that washing can be performed by an appropriate washing method according to the state of the filtration membrane, and high washing efficiency can be obtained. Furthermore, in the 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 water tank 20, but is circulated through the circulation flow path formed by the circulation piping 30 and the cleaning water piping 4 and supplied to the first water collection port 36, so that the first cleaning water 21 containing contaminants does not enter the first cleaning water tank 20. Therefore, it is not necessary to clean the first cleaning water tank 20 after cleaning the filtration membrane, and it is only necessary to refill the first cleaning water tank 20 with the amount of first cleaning water 21 used.

Furthermore, the filtration membrane cleaning device according to embodiment 1 includes a second cleaning water pipe 29 equipped with a second cleaning water pump 27 that supplies second cleaning water 26 from the second cleaning water tank 25, and the membrane filtrate water pipe 14 is connected to the second cleaning water pipe 29 by a second switching valve 13, and the controller 35 performs one of cleanings selected from dead-end filtration cleaning and cross-flow filtration cleaning using the first cleaning water 21 as the cleaning water and the first cleaning water tank 20 as the cleaning water tank, and then performs dead-end filtration cleaning and cross-flow filtration cleaning using the second cleaning water 26 as the cleaning water and the second cleaning water tank 25 as the cleaning water tank. The first cleaning water pump 22, the first switching valve 12, the second cleaning water pump 27, the second switching valve 13, the circulation switching valve 11 and the circulation pump 32 are controlled to perform any one of the cleaning methods selected from the cleaning methods. Therefore, 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 second cleaning water tank 25, and the first cleaning water 21 remaining in the circulation flow path formed by the circulation piping 30 and the cleaning water piping 4 is not mixed into the second cleaning water tank 25, so that the concentration of the second cleaning water 26 does not decrease and the cleaning effect does not decrease.

Furthermore, in the filtration membrane cleaning device according to embodiment 1, the circulation pipe 30 is equipped with a circulation flow rate measuring device 31 that measures the circulation flow rate, which is the flow rate of the cleaning water flowing through the circulation pipe 30, and the controller 35 controls the supply of cleaning water from the cleaning water tank to the circulation flow path 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 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. Therefore, the flow rate of the cleaning water circulating through the circulation flow path in cross-flow filtration cleaning can be maintained, and a decrease in cleaning efficiency due to the permeation of the cleaning water from the filtration membrane to the treated water tank 2 can be prevented.

Although the present application describes exemplary embodiments, the various features, aspects, and functions described in the embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.
Therefore, countless modifications not illustrated are expected within the scope of the technology disclosed in this application, including, for example, modifying, adding, or omitting at least one component.

1. Water to be treated, 2. Water tank to be treated, 3. Filtration membrane module, 4. Cleaning 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 filtrate water piping, 15. Membrane filtration pump, 16. Membrane filtrate water flow rate meter, 17. Membrane filtrate water pressure gauge, 18. Membrane filtration water tank, 19. Membrane filtrate, 20. First cleaning water tank, 2 1. First cleaning water, 22. First cleaning water pump, 23. First cleaning water flow rate meter, 24. First cleaning water piping, 25. Second cleaning water tank, 26. Second cleaning water, 27. Second cleaning water pump, 28. Second cleaning water flow rate meter, 29. Second cleaning water piping, 30. Circulation piping, 31. Circulation flow rate 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 (3)

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 first cleaning water pipe including a first cleaning water pump for supplying the first cleaning water from the 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 including a circulation pump for circulating the cleaning water;
a controller for controlling the first wash water pump, the first switching valve, the circulation switching valve, and the circulation pump,
The controller includes:
The first cleaning water is the cleaning water, and the first cleaning water tank is the cleaning water tank.
a filtration membrane cleaning device, characterized in that the first cleaning water pump, the first switching valve, the circulation switching valve and the circulation pump are controlled to perform one of cleaning methods selected from dead-end filtration cleaning, in which the cleaning water from the cleaning water tank is supplied to both the first water collection inlet and the second water collection inlet, and cross-flow filtration cleaning, in which the cleaning water taken out from the second water collection inlet is circulated through a circulation flow path formed by the circulation piping and the cleaning water piping, and supplied to the first water collection inlet. a second cleaning water pipe 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 1, 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. 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 1 or 2, 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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