Wastewater treatment method

Abstract

The object of the present application is to achieve an increase in productivity of water treatment and to fully exert the membrane cleaning effect achieved by relaxation. The membrane filter element (18) is aerated and the filtration operation and the filtration stop operation are repeated as one cycle. An exhaust valve (62) connected to the gas retention chamber (52) is temporarily opened and then closed in conjunction with the start timing of the filtration stop operation of each cycle.

Description

Technical Field

[0001] This invention relates to a wastewater treatment method that separates wastewater into solid and liquid phases to produce treated water. Background Technology

[0002] In wastewater treatment systems using the membrane filtration activated sludge (MBR) process, it is unavoidable that fouling will accumulate on the membrane sheets during wastewater filtration, leading to increased permeation resistance. Therefore, wastewater filtration is typically stopped periodically, and only the membrane sheets are aerated to allow the fouling to detach from the membrane sheets.

[0003] In other words, the process of aerating the membrane filter cartridge and creating negative pressure on the secondary side (treated water side) to filter wastewater, along with the filtration shutdown process, constitutes a cycle, which is repeated continuously. The aeration during the filtration shutdown phase is called relaxation, and this cycle is called an intermittent filtration cycle.

[0004] Furthermore, the removal of dirt from the membrane is achieved through pressure pulses within the filter cartridge generated by the oscillation of the membrane sheet relative to the filter plate. Additionally, during filtration, a higher flux (permeate flux) results in a greater transmembrane pressure differential, a stronger force causing the membrane sheet to adhere to the filter plate, and a smaller pressure pulse within the filter cartridge. Therefore, to fully utilize the membrane cleaning effect achieved through relaxation, it is necessary to increase the proportion of filtration stop time in intermittent filtration cycles to ensure sufficient time for the transmembrane pressure differential to reach an equilibrium state (zero).

[0005] Patent documents 1 and 2 disclose a wastewater treatment method that uses an atmospheric vent valve located midway through the treated water piping system connecting the membrane separation tank and the treated water tank. In prior art wastewater treatment methods, when filtration stops, the atmospheric vent valve is opened to open a portion of the treated water piping system to the atmosphere, thereby balancing the transmembrane pressure difference of the membrane filter element.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2000-288543

[0009] Patent Document 2: Japanese Patent Application Publication No. 9-75686 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] However, if the proportion of time the filter stops in the intermittent filtration cycle is increased, although the membrane cleaning effect achieved through relaxation can be fully utilized, the amount of treated water produced per unit time decreases, and the productivity of the treated water (production efficiency) is reduced.

[0012] On the other hand, if the proportion of filtration stop time in the intermittent filtration cycle is reduced, the time for the transmembrane pressure difference of the membrane filter element to reach an equilibrium state after the filtration stop action begins is shortened, making it difficult to fully utilize the membrane cleaning effect achieved through relaxation.

[0013] Moreover, such as Figure 1 As shown, if the flux increases during the filtration process, the transmembrane pressure difference of the membrane filter element increases. After the filtration stops and starts, the transmembrane pressure difference of the membrane filter element may not reach an equilibrium state, causing the next filtration process to start and failing to fully utilize the membrane cleaning effect achieved through relaxation.

[0014] On the other hand, in existing wastewater treatment methods, because a portion of the treated water piping system is opened to the atmosphere when filtration stops, the time until filtration resumes is longer, thus reducing the productivity of the treated water.

[0015] Therefore, one objective of the present invention is to fully utilize the membrane cleaning effect achieved through relaxation while improving the productivity of water treatment.

[0016] means for solving problems

[0017] One aspect of the present invention relates to a wastewater treatment method that involves aerating a membrane filter element immersed in a membrane separation tank for wastewater (treated water), and performing a filtration operation that creates negative pressure on the secondary side (treated water side) of the membrane filter element to filter the wastewater, and performing a filtration stop operation that stops the filtration operation as a cycle, and repeating this cycle to achieve solid-liquid separation of wastewater to generate treated water. A valve is used, connected to a gas retention chamber that retains gases contained in the treated water and for supplying fluid to the gas retention chamber. The valve is temporarily opened and then closed in conjunction with the start time of the filtration stop operation in each cycle.

[0018] Invention Effects

[0019] According to one aspect of the present invention, it is possible to improve the productivity of water treatment and fully utilize the membrane cleaning effect achieved through relaxation. Attached Figure Description

[0020] Figure 1 This is a graph illustrating previous research topics, and it shows the relationship between the transmembrane pressure difference of the membrane filter element and time.

[0021] Figure 2 This is a schematic diagram of a wastewater treatment system used to implement the wastewater treatment method involved in Embodiment 1.

[0022] Figure 3 It is a timing diagram showing the relationship between aeration, filtration, and filtration shutdown actions and the opening and closing actions of the exhaust valve or atmospheric opening valve.

[0023] Figure 4 This is a schematic diagram of a wastewater treatment system used to implement the wastewater treatment method involved in Embodiment 2. Detailed Implementation

[0024] [Implementation Method 1]

[0025] The following is for reference Figure 2 and Figure 3 The embodiments of the present invention will be described. Figure 2 This is a schematic diagram of a wastewater treatment system used to implement the wastewater treatment method involved in Embodiment 1. Figure 3 It is a timing diagram showing the relationship between aeration, filtration, and filtration shutdown actions and the opening and closing of the exhaust valve.

[0026] (Wastewater treatment system 10)

[0027] like Figure 2 As shown, the wastewater treatment system 10 used to implement the wastewater treatment method according to Embodiment 1 is a system that uses a membrane separation activated sludge process (MBR) to perform solid-liquid separation of wastewater (treated water) E to generate treated water (filtrate) T. The wastewater treatment system 10 includes a membrane separation tank 12 for storing wastewater E. A water level gauge 14 for detecting the water level of wastewater E in the membrane separation tank 12 is installed at an appropriate position in the membrane separation tank 12.

[0028] A membrane module 16 for solid-liquid separation of wastewater E is disposed within a membrane separation tank 12. The membrane module 16 is immersed in the wastewater E within the membrane separation tank 12. The membrane module 16 has a plurality of flat membrane filter elements 18 arranged side by side in an upright state. Each membrane filter element 18 has a filter plate 20 and membrane sheets 22 disposed on two sides of the filter plate 20. The periphery of each membrane sheet 22 is fixed to the side of each filter plate 20. Since the parts of each membrane sheet 22 other than the periphery are not fixed to each filter plate 20, each membrane sheet 22 can swing relative to each filter plate 20. Passages for the flow of treated water (filtrate) T through the membrane sheets 22 are formed between each filter plate 20 and each membrane sheet 22, and inside each filter plate 20.

[0029] An aeration device 24 for aerating a plurality of membrane filter elements 18 is disposed on the lower side of the membrane module 16 within the membrane separation tank 12. The aeration device 24 is connected to a blower (not shown) that generates compressed air. The aeration device 24 supplies compressed air to the plurality of membrane filter elements 18 for membrane surface cleaning and also supplies oxygen to the activated sludge contained in the wastewater. Thus, the membrane separation tank 12 becomes an aerobic environment, utilizing the activated sludge for nitrification treatment of the wastewater.

[0030] The wastewater treatment system 10 includes a treatment water tank 26 for storing treated water T, which is located separately from the membrane separation tank 12. The water level of the treated water T in the treatment water tank 26 is lower than the water level of the wastewater E in the membrane separation tank 12.

[0031] The wastewater treatment system 10 includes a treated water piping system 28 that connects the membrane separation tank 12 and the treated water tank 26. The specific structure of the treated water piping system 28 is as follows.

[0032] One end of the first piping 30 is connected to the membrane module 16, and the other end of the first piping 30 is connected to a manifold 32 for containing the treated water T generated by the membrane module 16. The manifold 32 is located at a position higher than the water level of the treated water T in the membrane separation tank 12. In addition, one end of the second piping 34 is connected to the manifold 32, and the other end of the second piping 34 is connected to the treated water tank 26. On the second piping 34, from the manifold 32 side (upstream side), a pressure gauge 36 for detecting the pressure corresponding to the transmembrane pressure difference of the membrane filter element 18, a flow meter 38 for detecting the flow rate of the treated water T, a regulating valve 40, and a shut-off valve 42 are sequentially arranged.

[0033] One end of the third pipe 44 is connected between the flow meter 38 and the regulating valve 40 of the second pipe 34, and the other end of the third pipe 44 is connected to the treatment tank 26. On the third pipe 44, a suction valve 46, a suction pump 48 and a shut-off valve 50 are sequentially installed from one end of the third pipe 44.

[0034] According to the above structure, during gravity filtration, the computer-controlled device closes the suction valve 46 and opens the shut-off valve 42, adjusting the opening of the regulating valve 40 to adjust the filtration volume. Thus, due to the water level difference between the membrane separation tank 12 and the treated water tank 26, a negative pressure is generated on the secondary side (treated water side) of the plurality of membrane filter elements 18, performing gravity filtration of wastewater E. Furthermore, during the filtration stop operation to cease gravity filtration, the control device closes the shut-off valve 42.

[0035] During the suction filtration operation, the control device closes the shut-off valve 42 and opens the suction valve 46 and shut-off valve 50. Then, the control device drives the suction pump 48. The suction force of the suction pump 48 creates a negative pressure on the secondary side (treated water side) of the plurality of membrane filter elements 18, thus performing the suction filtration of wastewater E. Furthermore, during the filtration stop operation, the control device stops the drive of the suction pump 48 and closes the shut-off valve 50.

[0036] In addition, the aforementioned control device switches between gravity filtration and suction filtration based on the detection results from the water level gauge 14 and the flow meter 38.

[0037] A gas retention chamber 52 is provided at the upper part of the manifold 32 to retain the gas contained in the treated water T. The gas retention chamber 52 is in communication with the interior of the manifold 32. A level gauge 54 is provided at an appropriate position in the gas retention chamber 52 to detect the water level of the treated water T within the gas retention chamber 52. Alternatively, the gas retention chamber 52 may be a gas retention tank that is separate from the manifold 32 and located at a higher position than the manifold 32. The gas contained in the treated water T is mainly air, but is not limited to air.

[0038] The wastewater treatment system 10 includes an exhaust piping system 56 that connects the gas retention chamber 52 and the treatment water tank 26. The specific structure of the exhaust piping system 56 is as follows.

[0039] One end of the fourth pipe 58 is connected to the gas retention chamber 52, and the other end of the fourth pipe 58 is connected to an ejector 60 that generates negative pressure. An exhaust valve 62 for venting gas retained in the gas retention chamber 52 is installed midway through the fourth pipe 58. The exhaust valve 62 is connected to the gas retention chamber 52 via the fourth pipe 58. Additionally, one end of the fifth pipe 64 is connected to the ejector 60, and the other end of the fifth pipe 64 is connected to the treatment water tank 26. On the fifth pipe 64, starting from the ejector 60 side, a check valve 66 to prevent backflow to the treatment water tank 26 and an ejector pump 68 are sequentially installed.

[0040] One end of the sixth pipe 70 is connected to the ejector 60, and the other end of the sixth pipe 70 is open to the atmosphere. A funnel 72 for recovering treated water T is provided on the lower side of the other end of the sixth pipe 70. One end of the seventh pipe 74 is connected to the funnel 72, and the other end of the seventh pipe 74 is connected to the treated water tank 26.

[0041] According to the above structure, when the water level gauge 54 detects a predetermined first low water level, the control device drives the jet pump 68 and opens the vent valve 62. This allows high-speed treated water T to be supplied to the ejector 60, creating negative pressure in the ejector 60. Consequently, the gas in the gas retention chamber 52 is drawn in and released to the atmosphere via the fourth pipe 58 and the sixth pipe 70. At this time, a portion of the treated water T drawn in along with the gas in the gas retention chamber 52 is recovered into the treated water tank 26 via the fourth pipe 58, the ejector 60, the sixth pipe 70, the funnel 72, and the seventh pipe 74. The predetermined first low water level refers to a water level lower than the reference water level, which is the water level at which the gas in the gas retention chamber 52 needs to be discharged. Furthermore, the reference water level refers to the reference water level at which the vent valve 62 is closed.

[0042] When the water level gauge 54 detects the reference water level, the aforementioned control device closes the vent valve 62 and stops driving the jet pump 68. Consequently, the suction of gas in the gas retention chamber 52 ceases, and the treated water T accumulates between the vent valve 62 and the jet pump 60 in the fourth piping 58.

[0043] Furthermore, the aforementioned control device may also perform the opening and closing of the exhaust valve 62 periodically, rather than based on the detection results of the water level gauge 54.

[0044] As described above, treated water T accumulates between the vent valve 62 and the injector 60 in the fourth piping 58. Therefore, when the vent valve 62 is opened, a portion of the treated water T accumulated between the vent valve 62 and the injector 60 in the fourth piping 58 is supplied to the gas retention chamber 52. That is, the vent valve 62 is a valve for venting the gas retained in the gas retention chamber 52, and also a valve for supplying treated water T as a fluid to the gas retention chamber 52.

[0045] (Wastewater treatment methods)

[0046] like Figure 2 and Figure 3 As shown, the wastewater treatment method in Embodiment 1 involves aerating multiple membrane filter elements 18 immersed in a membrane separation tank 12 for wastewater E, and repeatedly performing a filtration operation and a filtration stop operation as a cycle (intermittent filtration cycle) to achieve solid-liquid separation of wastewater E and generate treated water T. The filtration operation refers to the action of generating negative pressure on the secondary side of the multiple membrane filter elements 18 to filter wastewater E, including gravity filtration and suction filtration. The filtration stop operation refers to the action of stopping the filtration operation.

[0047] Furthermore, in the wastewater treatment method according to Embodiment 1, the above-mentioned control device is coordinated with the start time of the filtration stop operation of each intermittent filtration cycle to temporarily open and then close the exhaust valve 62 so as not to generate airlock (bubbles) in the treated water piping system 28.

[0048] Specifically, the aforementioned control device temporarily opens the exhaust valve 62 at the same time as or immediately after the start of the filtration stop operation in each cycle, and then closes it after a predetermined time (e.g., 1 second). The opening degree of the exhaust valve 62 does not need to be fully open; it can be a slight opening as long as it can supply an appropriate amount of treated water T to the gas retention chamber 52.

[0049] During repeated intermittent filtration cycles, when the water level gauge 54 detects a predetermined second low water level, the control device drives the jet pump 68 and opens the vent valve 62. As a result, the gas in the gas retention chamber 52 is released, and the water level of the treated water T in the gas retention chamber 52 rises. Then, when the water level gauge 54 detects a reference water level, the control device closes the vent valve 62 and stops driving the jet pump 68. The predetermined second low water level refers to a water level lower than the predetermined first low water level, specifically the water level before airlock occurs in the treated water piping system 28. In other words, the predetermined second low water level is the water level used to prevent airlock in the treated water piping system 28.

[0050] The control device described above may not temporarily open the exhaust valve 62 at the same time as or immediately after the start of the filter stop action in each cycle, and then close it after a specified time. Instead, it may adopt the following method.

[0051] The aforementioned control device temporarily opens the vent valve 62 at the same time as or immediately after the start of the filtration stop action in each intermittent filtration cycle, and closes the vent valve 62 when the transmembrane pressure difference of the plurality of membrane filter elements 18 becomes zero. The aforementioned control device determines that the transmembrane pressure difference of the plurality of membrane filter elements 18 becomes zero based on the detection result from the pressure gauge 36.

[0052] (Effects)

[0053] As described above, the control device, in coordination with the start time of the filtration stop operation of each intermittent filtration cycle, temporarily opens and then closes the vent valve 62. Thus, in coordination with the start time of the filtration stop operation of each intermittent filtration cycle, a portion of the treated water T accumulated in the fourth piping 58 between the vent valve 62 and the ejector 60 is supplied to the gas retention chamber 52. Consequently, the negative pressure on the secondary side of the plurality of membrane filter elements 18 is alleviated, and the transmembrane pressure difference of the plurality of membrane filter elements 18 becomes balanced. In other words, without opening a portion of the treated water piping system 28 to the atmosphere, while maintaining the continuous presence of treated water in the treated water piping system 28 (forming a siphon state), the transmembrane pressure difference of the plurality of membrane filter elements 18 is balanced within a short time after the start of the filtration stop operation of each intermittent filtration cycle. This increases the flux (permeate flux), improves the productivity (production efficiency) of the treated water T of the wastewater treatment system 10, and fully utilizes the membrane cleaning effect achieved through relaxation.

[0054] Furthermore, as described above, the control device coordinates with the start time of the filtration stop operation of each intermittent filtration cycle to temporarily open and then close the exhaust valve 62, thereby preventing airlock in the treated water piping system. This ensures stable filtration operation for each intermittent filtration cycle.

[0055] Therefore, according to the wastewater treatment method of Embodiment 1, the productivity of the treated water T of the wastewater treatment system 10 can be improved, the membrane cleaning effect achieved by relaxation can be fully utilized, and the filtration operation of each intermittent filtration cycle can be performed stably.

[0056] [Implementation Method 2]

[0057] The following is for reference Figure 3 and Figure 4 Embodiment 2 of the present invention will be described. Figure 3 It is a timing diagram showing the relationship between aeration, filtration, filtration shutdown, and the opening and closing of the atmospheric opening valve.

[0058] Figure 4 This is a schematic diagram of a wastewater treatment system used to implement the wastewater treatment method according to Embodiment 2. Furthermore, for ease of explanation, components having the same functions as those described in the embodiments of the present invention are labeled with the same reference numerals, and their descriptions are not repeated.

[0059] (Wastewater treatment system)

[0060] like Figure 4As shown, the wastewater treatment system 10A used to implement the wastewater treatment method according to Embodiment 2 is a system that uses a membrane separation activated sludge process (MBR) to perform solid-liquid separation on wastewater E to generate treated water T. The wastewater treatment system 10A has the same structure as the wastewater treatment system 10, and only the differences between the two systems will be described.

[0061] One end of the eighth piping 76 is connected to a gas retention chamber 52, and the other end of the eighth piping 76 is connected to an atmospheric release valve 78 for opening the gas retention chamber 52 to the atmosphere. The atmospheric release valve 78 is connected to the gas retention chamber 52 via the eighth piping 76. When the atmospheric release valve 78 is open, the gas retention chamber 52 is opened to the atmosphere, and air (atmosphere) is supplied to the gas retention chamber 52. That is, the atmospheric release valve 78 is a valve for opening the gas retention chamber 52 to the atmosphere and a valve for supplying air as a fluid to the gas retention chamber 52.

[0062] (Wastewater treatment methods)

[0063] like Figure 3 and Figure 4 As shown, the wastewater treatment method according to Embodiment 2 involves aerating multiple membrane filter elements 18 of wastewater E immersed in the membrane separation tank 12, and repeatedly performing the filtration operation and filtration stop operation as a cycle (intermittent filtration cycle) to separate solids and liquids in wastewater E to generate treated water T. Furthermore, in the wastewater treatment method according to Embodiment 2, the aforementioned control device, in coordination with the start time of the filtration stop operation of each intermittent filtration cycle, temporarily opens and then closes the atmospheric vent valve 78 to prevent airlock (bubbles) from forming in the treated water piping system 28.

[0064] Specifically, the aforementioned control device temporarily opens the atmospheric opening valve 78 at the same time as or immediately after the start of the filtration stop operation in each cycle, and then closes it after a predetermined time (e.g., 1 second). The opening degree of the atmospheric opening valve 78 does not need to be fully open; it can be a slight opening as long as it can supply an appropriate amount of air to the gas retention chamber 52.

[0065] The aforementioned control device may not temporarily open the atmospheric opening valve 78 at the same time as or immediately after the start of the filtration stop action in each cycle, and then close it after a specified time. Instead, it may adopt the following method.

[0066] The aforementioned control device temporarily opens the atmospheric opening valve 78 at the same time as or immediately after the start of the filtration stop action of each intermittent filtration cycle, and closes the atmospheric opening valve 78 when the transmembrane pressure difference of the plurality of membrane filter elements 18 becomes zero.

[0067] (Effects)

[0068] As described above, the control device, in coordination with the start time of the filtration stop operation of each intermittent filtration cycle, temporarily opens and then closes the atmospheric opening valve 78. This, in coordination with the start time of the filtration stop operation of each intermittent filtration cycle, supplies air to the gas retention chamber 52. Consequently, the negative pressure on the secondary side of the plurality of membrane filter elements 18 is alleviated, and the transmembrane pressure difference of the plurality of membrane filter elements 18 becomes balanced. In other words, without opening a portion of the treated water piping system 28 to the atmosphere, while maintaining the continuous presence of treated water in the treated water piping system 28 (forming a siphon state), the transmembrane pressure difference of the plurality of membrane filter elements 18 is balanced within a short period after the start of the filtration stop operation of each intermittent filtration cycle. This increases the flux, improves the productivity (production efficiency) of the treated water T of the wastewater treatment system 10A, and fully utilizes the membrane cleaning effect achieved through relaxation.

[0069] Furthermore, as described above, the control device, in coordination with the start time of the filtration stop operation of each intermittent filtration cycle, temporarily opens and then closes the atmospheric vent valve 78 to prevent airlock in the treated water piping system. This ensures stable filtration operation for each intermittent filtration cycle.

[0070] In other words, according to the wastewater treatment method described in Embodiment 2, the productivity of the treated water T of the wastewater treatment system 10A can be improved, the membrane cleaning effect achieved by relaxation can be fully utilized, and the filtration action of each intermittent filtration cycle can be performed stably.

[0071] 〔Summarize〕

[0072] The wastewater treatment method according to Embodiment 1 of the present invention involves aerating a membrane filter element immersed in a membrane separation tank for wastewater (treated water), and performing a filtration operation that creates negative pressure on the secondary side (treated water side) of the membrane filter element to filter the wastewater, and performing a filtration stop operation that stops the filtration operation as a cycle, and repeating this cycle to achieve solid-liquid separation of wastewater to generate treated water. A valve is used to supply fluid to a gas retention chamber that retains gas contained in the treated water, and the valve is temporarily opened and then closed in conjunction with the start time of the filtration stop operation in each cycle.

[0073] According to the above structure, the valve is temporarily opened and then closed in conjunction with the start time of the filtration stop operation in each cycle. This, in conjunction with the start time of the filtration stop operation in each cycle, supplies fluid to the gas retention chamber. Consequently, the negative pressure on the secondary side of the membrane filter element is alleviated in a short time, and the transmembrane pressure difference of the membrane filter element becomes balanced. In other words, without opening a portion of the treated water piping system connecting the membrane separation tank and the treated water tank to the atmosphere, while maintaining the continuous presence of treated water within the treated water piping (forming a siphon state), the transmembrane pressure difference of the membrane filter element becomes balanced after the start of the filtration stop operation in each cycle. Therefore, the productivity (production efficiency) of the treated water can be improved, and the membrane cleaning effect achieved through relaxation can be fully utilized.

[0074] In the wastewater treatment method according to Embodiment 2 of the present invention, in Embodiment 1, the valve may also be an exhaust valve disposed in the middle of the piping connecting the ejector for generating negative pressure and the gas retention chamber.

[0075] According to the above structure, the exhaust valve is temporarily opened and then closed in conjunction with the start time of the filtration stop operation in each cycle. Thus, in conjunction with the start time of the filtration stop operation in each cycle, treated water is supplied to the gas retention chamber.

[0076] In the wastewater treatment method of embodiment 3 of the present invention, in embodiment 1, the valve may also be an atmospheric opening valve for opening the gas retention chamber to the atmosphere.

[0077] According to the above structure, the atmospheric opening valve is temporarily opened and then closed in conjunction with the start time of the filtration stop operation in each cycle. Thus, air is supplied to the gas retention chamber in conjunction with the start time of the filtration stop operation in each cycle.

[0078] In any of the above methods 1 to 3, the wastewater treatment method according to method 4 of the present invention may also be coordinated with the start time of the filtration stop operation of each cycle by temporarily opening and then closing the valve so as not to generate airlock (bubbles) in the treatment water piping system that connects the membrane separation tank and the treatment water tank for storing treatment water.

[0079] Based on the above structure, the valve is temporarily opened and then closed in conjunction with the start time of the filtration stop operation in each cycle, so as to prevent airlock from occurring in the treated water piping system. This ensures that the filtration operation in each cycle can be performed stably.

[0080] In the wastewater treatment method according to embodiment 5 of the present invention, in any of the embodiments 1 to 3 above, the valve may be temporarily opened at the same time as or immediately after the start of the filtration stop action in each cycle, and the valve may be closed when the transmembrane pressure difference of the membrane filter element becomes zero.

[0081] According to the above structure, the valve is temporarily opened at the same time as or immediately after the start of the filtration stop operation in each cycle, and the valve is closed when the transmembrane pressure difference of the membrane filter element becomes zero. Thus, fluid can be supplied to the gas retention chamber in conjunction with the start time of the filtration stop operation in each cycle, so that the transmembrane pressure difference of the membrane filter element reaches an equilibrium state.

[0082] [Notes]

[0083] This invention is not limited to the above-described embodiments. Various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of this invention.

[0084] Explanation of reference numerals in the attached figures

[0085] 10 Wastewater Treatment System

[0086] 12 Membrane Separation Tank

[0087] 14. Water level gauge

[0088] 16 Membrane Modules

[0089] 18 Membrane filter element

[0090] 20 filter plates

[0091] 22 membranes

[0092] 24 Aeration device

[0093] 26. Water Treatment Tank

[0094] 28. Water treatment piping system

[0095] 30 First Pipeline

[0096] 32 manifolds

[0097] 34 Second piping

[0098] 36 Pressure gauge

[0099] 38 Flow Meter

[0100] 40 Control valve

[0101] 42. Close valve

[0102] 44 Third Piping

[0103] 46 Suction valve

[0104] 48 Suction Pump

[0105] 50 Close valve

[0106] 52 Gas Retention Chamber

[0107] 54 Water level gauge

[0108] 56. Exhaust piping system

[0109] 58 Fourth piping

[0110] 60 injectors

[0111] 62 Exhaust valve

[0112] 64 Fifth Pipeline

[0113] 66 Check valve

[0114] 68 Jet Pump

[0115] 70 Sixth Pipeline

[0116] 72 Funnel

[0117] 74 Seventh Pipeline

[0118] 10A Wastewater Treatment System

[0119] 76 Eighth Pipeline

[0120] 78 Atmospheric Opening Valve

[0121] E Wastewater (treated water)

[0122] T is the treated water (filtrate).

Claims

1. A wastewater treatment method, comprising aerating a membrane filter element immersed in a membrane separation tank, and performing a filtration action—creating negative pressure on the secondary side of the membrane filter element to filter the wastewater—and a filtration stopping action—which constitutes a cycle, and repeating this cycle, thereby achieving solid-liquid separation of wastewater to generate treated water, characterized in that... A valve is used to supply fluid to a gas retention chamber that traps gases contained in the treated water, and the valve is temporarily opened and then closed at the same time as or immediately after the start of the filtration stop operation in each cycle.

2. The wastewater treatment method according to claim 1, characterized in that, The valve is an exhaust valve located midway in the piping connecting the negative pressure injector and the gas retention chamber.

3. The wastewater treatment method according to claim 1, characterized in that, The valve is an atmospheric opening valve used to open the gas retention chamber to the atmosphere.

4. The wastewater treatment method according to any one of claims 1 to 3, characterized in that, The valve is temporarily opened and then closed at the same time as or immediately after the start of the filtration stop operation in each cycle, so as to prevent airlock from occurring in the treated water piping system that connects the membrane separation tank and the treated water storage tank.

5. The wastewater treatment method according to any one of claims 1 to 3, characterized in that, The valve is temporarily opened at the same time as or after the start of the filtration stop action in each cycle, and closed when the transmembrane pressure difference of the membrane filter element becomes zero.

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