Water treatment method and water treatment apparatus

Abstract

This invention provides a water treatment method that can remove the microbial layer from the surface of a gas permeable membrane even if bridging occurs in a hollow fiber membrane element. [Solution] A water treatment method for purifying water containing ammonia nitrogen to obtain treated water, comprising: a normal operation step in which a hollow fiber membrane element, which is a gas permeable membrane, is immersed in the water to be treated and air is circulated through the gas flow passage to form a microbial layer on the surface of the hollow fiber membrane, the element comprising: a normal operation step in which the microbial layer is peeled off from the surface of the hollow fiber membrane after the normal operation step, the microbial layer peeling step in which air is supplied to the gas flow passage from the other while one of the inlet and outlet of the gas flow passage is sealed.

Description

[Technical Field]

[0001] The present invention relates to a water treatment method and a water treatment apparatus. [Background Art]

[0002] Water to be treated such as groundwater, river water, industrial wastewater and domestic wastewater often contains organic substances such as ammonia. After water treatment for removing organic substances including ammonia is performed, the water is reused as domestic water or industrial water, or discharged into rivers or the like. As a water treatment method, water treatment using a so-called membrane aeration biofilm reactor (MABR) has been proposed, which is a bioreactor that forms a microbial layer (biofilm) derived from microorganisms in the water to be treated on the surface of a hollow fiber membrane that is a gas permeable membrane, and supplies oxygen to the microbial layer from the inner surface side of the hollow fiber membrane. In water treatment using MABR, an oxygen gradient is formed in the thickness direction of the microbial layer. Aerobic treatment (BOD oxidation, nitrification of ammonia) proceeds on the inner layer side of the microbial layer, and anaerobic treatment of nitric acid (BOD oxidation, denitrification treatment) proceeds on the outer layer side of the microbial layer.

[0003] In a water treatment apparatus using MABR, for example, a plurality of hollow fiber membranes are gathered into a sheet shape, and a hollow fiber membrane element having gas pipes connected to the upper and lower sides thereof is immersed in wastewater that is the water to be treated. When the microbial layer on the surface of the hollow fiber membrane (gas permeable membrane) of the hollow fiber membrane element excessively adheres and grows, the microbial layers of adjacent hollow fiber membranes connect to each other, causing a bridging phenomenon in which a continuous microbial layer is formed between the membranes. When the bridging phenomenon occurs, neither the aerobic treatment on the inner layer side of the microbial layer nor the anaerobic treatment on the outer layer side is performed at all, and the water to be treated is discharged from the treatment tank as it is, causing a situation where the water quality of the treated water deteriorates.

[0004] Patent Document 1 proposes a method using a hollow fiber membrane module equipped with a liquid treatment membrane element for filtering and sucking up water to be treated, in addition to a gas permeable membrane element. If the pressure when filtering and sucking up the water to be treated is higher than an appropriate value, it is determined that there is a large amount of microbial layer attached to the surface of the gas permeable membrane. Then, aeration is performed using an aeration device placed below the hollow fiber membrane module, and the microbial layer formed on the surface of the gas permeable membrane is removed by rising bubbles. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-85958 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the method described in Patent Document 1, if bridging occurs, even if aeration is performed, the bubbles will not reach between the membranes, making it difficult to remove the microbial layer attached to the surface of the gas permeable membrane. The present invention aims to provide a water treatment method and a water treatment apparatus that can remove the microbial layer on the surface of a gas permeable membrane even if a bridging phenomenon occurs in a hollow fiber membrane element. [Means for solving the problem]

[0007] In view of the above problems, the inventors of the present invention have discovered that after normal operation, air is supplied into the gas flow passage in the hollow fiber membrane element while the gas flow passage is sealed, and the microbial layer is detached by the high pressure of nitrogen in the air, thereby completing the present invention. Specifically, the present invention has the following aspects. <1> A water treatment method for obtaining treated water by purifying water containing ammonia nitrogen, A normal operation process involves immersing a hollow fiber membrane element, which comprises multiple hollow fiber membranes that are gas permeable membranes and has gas flow passages for circulating gas in the hollow portions of the hollow fiber membranes, in the water to be treated, and circulating air through the gas flow passages to form a microbial layer on the surface of the hollow fiber membranes, The process includes, after the normal operation step, a microbial layer peeling step in which the microbial layer is peeled off from the surface of the hollow fiber membrane. A water treatment method comprising the microbial layer removal step, wherein one of the inlet and outlet of the gas flow passage is sealed, and air is supplied to the gas flow passage from the other. <2> The internal pressure of the gas flow passage in the microbial layer removal process is set to be 1.5 times or more the outlet pressure of the gas flow passage in the normal operation process. <1> The water treatment method described above. <3> The system further includes a control step for initiating the microbial layer peeling step based on the water quality of the treated water. <1> or <2> The water treatment method described above. <4> Multiple hollow fiber membrane units, each comprising multiple hollow fiber membrane elements, are immersed in the water to be treated. The plurality of hollow fiber membrane units have a period during which some of them perform the normal operation process and the rest perform the microbial layer peeling process. <1> ~ <3> A water treatment method described in any of the following. <5> A water treatment apparatus that purifies water to be treated containing ammonia nitrogen to obtain treated water, A hollow fiber membrane element comprising multiple hollow fiber membranes which are gas permeable membranes, and having a gas flow passage for circulating gas in the hollow portion of the hollow fiber membranes, A means for dispersing air is provided below the hollow fiber membrane element, A gas supply means for supplying gas to the aforementioned gas flow passage, A gas flow rate adjustment means for adjusting the flow rate of gas discharged from the gas flow passage, A water treatment apparatus comprising: a control means for adjusting the opening degree of the gas flow rate adjustment means based on the water quality of the treated water. <6> The control means adjusts the opening of the gas flow rate adjustment means and the discharge pressure of the gas supply means based on the water quality of the treated water. <5> The water treatment apparatus described above. [Effects of the Invention]

[0008] According to the present invention, a water treatment method and a water treatment apparatus are provided that can remove the microbial layer on the surface of a gas permeable membrane even if a bridging phenomenon occurs in a hollow fiber membrane element. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing a water treatment apparatus according to one embodiment. [Figure 2] This is a front view showing a hollow fiber membrane element according to one embodiment. [Figure 3] Figure 2 is a perspective view of the hollow fiber membrane element. [Figure 4] This is a perspective view showing a hollow fiber membrane unit according to one embodiment. [Modes for carrying out the invention]

[0010] In this specification and the claims, when "~" is used to indicate a numerical range, that range includes the numbers written before and after "~" as the lower and upper limits. For example, "A~B" means A or greater and B or less.

[0011] ≪Water Treatment Equipment≫ Figure 1 is a schematic diagram showing an example of a water treatment apparatus 200 according to an embodiment. The dimensions and other specifications of the figures illustrated in the following description are examples only, and the present invention is not necessarily limited thereto. It can be implemented with appropriate modifications without changing the essence of the invention. The water treatment device 200 comprises a hollow fiber membrane unit 100 having a plurality of hollow fiber membrane elements 1, an aeration means 4, a gas supply means 31, a gas flow rate adjustment means 32, and a control means 35. Air is used as the gas supplied to the hollow fiber membrane elements 1. The water treatment apparatus 200 is suitably used for water treatment that purifies treated water containing ammonia nitrogen to obtain treated water. Examples of treated water containing ammonia nitrogen include industrial wastewater from ironworks, refineries, chemical plants, plating plants, fertilizer plants and the like, and natural water such as groundwater and river water.

[0012] [Hollow Fiber Membrane Element] Figure 2 is a front view of the hollow fiber membrane element 1, and Figure 3 is a perspective view of the hollow fiber membrane element 1. The hollow fiber membrane element 1 includes a hollow fiber membrane sheet 10 composed of a plurality of hollow fiber membranes 11, a first gas passage pipe 12, a second gas passage pipe 14, a first support column 16, and a second support column 18. The interiors of the first gas passage pipe 12, the hollow fiber membrane 11, the second gas passage pipe 14, and the second support column 18 communicate with each other, forming a gas flow passage through which gas flows into the hollow portion of the hollow fiber membrane 11.

[0013] In the hollow fiber membrane element 1, the first gas passage pipe 12 is arranged on the upper side, and the second gas passage pipe 14 is arranged on the lower side, such that the first gas passage pipe 12 and the second gas passage pipe 14 each extend in the horizontal direction. Both ends of the first support column 16 are connected to a first end 12a of the first gas passage pipe 12 and a first end 14a of the second gas passage pipe 14, and both ends of the second support column 18 are connected to a second end 12b of the first gas passage pipe 12 and a second end 14b of the second gas passage pipe 14. In this way, the first gas passage pipe 12 and the second gas passage pipe 14 are supported by the first support column 16 and the second support column 18 extending in the vertical direction, forming a rectangular frame shape.

[0014] The hollow fiber membrane sheet 10 is formed by aligning a plurality of hollow fiber membranes 11 in a sheet shape, and is positioned between the first support column 16 and the second support column 18, with the upper end of each hollow fiber membrane 11 connected to the first gas passage pipe 12 and the lower end of each hollow fiber membrane 11 connected to the second gas passage pipe 14. Each hollow fiber membrane 11 has its length in the vertical direction and is parallel to the first support column 16 and the second support column 18. The distance between the first gas passage pipe 12 and the second gas passage pipe 14 is kept constant by the support from the first support column 16 and the second support column 18, thereby forming a flat hollow fiber membrane element 1 in which the surface shape of the hollow fiber membrane sheet 10 is maintained. Furthermore, the hollow fiber membrane element 1 is not limited to a flat shape; for example, it can also be configured in a cylindrical or rectangular shape.

[0015] The upper end of each hollow fiber membrane 11 is attached to the first gas passage pipe 12 such that the inside (hollow portion) of the hollow fiber membrane 11 communicates with the flow path 13 inside the first gas passage pipe 12. The lower end of each hollow fiber membrane 11 is attached to the first gas passage pipe 12 such that the inside of the hollow fiber membrane 11 communicates with the flow path 15 inside the second gas passage pipe 14. The method of attaching the upper end of each hollow fiber membrane 11 to the first gas passage pipe 12 is not particularly limited, and known methods can be adopted. For example, one method is to fix each hollow fiber membrane 11 to the first gas passage pipe 12 with potting resin, with the upper end surface of each hollow fiber membrane 11 open inside the first gas passage pipe 12. The method of attaching the lower end of each hollow fiber membrane 11 to the second gas passage pipe 14 is similar. That is, for example, one method is to fix the lower end of each hollow fiber membrane 11 to the second gas passage pipe 14 with potting resin, with the lower end surface of each hollow fiber membrane 11 open inside the second gas passage pipe 14.

[0016] Examples of potting resins include epoxy resins, unsaturated polyester resins, polyurethane resins, silicone-based fillers, and various hot-melt resins. The potting resin forming the potted portion may be one type or two or more types.

[0017] The number of hollow fiber membranes 11 constituting the hollow fiber membrane sheet 10 is not particularly limited and can be, for example, 10,000 to 50,000. The hollow fiber membrane sheet-like material 10 may consist of a single sheet made up of multiple hollow fiber membranes 11, or it may consist of a laminate in which multiple sheets made up of multiple hollow fiber membranes 11 are stacked together.

[0018] The hollow fiber membrane 11 is a gas permeable membrane. For example, as the hollow fiber membrane 11, a hollow fiber gas permeable membrane used in water treatment by MABR, that is, a water treatment gas permeable membrane on which a microbial layer derived from microorganisms or bacteria in the wastewater is formed on the surface can be used. More specifically, a hollow fiber membrane that can permeate oxygen from the inner side to the surface by supplying oxygen to the hollow part can be used, and a hollow fiber membrane including a non-porous layer, which will be described later, is preferred.

[0019] The shape of the hollow fiber membrane 11 is not particularly limited, and for example, a roughly cylindrical shape can be given as an example. However, "roughly cylindrical" means a three-dimensional shape in which the shape of any cross-section perpendicular to the longitudinal direction is, for example, a perfect circle, egg, oblong, ellipse, or other oval shape.

[0020] The hollow fiber membrane 11 may be a single-layer membrane or a multi-layer membrane.

[0021] An example of a hollow fiber membrane consisting of a single layer is a hollow fiber membrane consisting of a non-porous layer. The material used to form the single layer film is not limited, but examples include polyolefin resins, polyurethane resins, fluororesins, and silicone resins. The above materials may be used individually or in combination of two or more types. Examples of polyolefin resins used include polyethylene, polypropylene, and polymethylpentene. From the viewpoint of cost and productivity, it is preferable that the polyolefin resin is formed to include polyethylene. From the viewpoint of oxygen transport rate, it is more preferable that the polyolefin resin is formed to include low-density polyethylene (LDPE). Furthermore, from the viewpoint of oxygen permeability and oxygen transport rate, it is preferable that the silicone resin is formed containing polydimethylsiloxane (PMDS).

[0022] The thickness of the single-layer film is preferably 5 μm to 100 μm, more preferably 10 μm to 70 μm, and even more preferably 15 μm to 50 μm. If the thickness of the single-layer film is less than 30 μm, it is preferable to provide a reinforcing structure to sufficiently increase the mechanical strength of the film.

[0023] An example of a hollow fiber membrane consisting of multiple layers is a three-layer hollow fiber membrane in which a non-porous layer is arranged between two porous layers. Each of the two porous layers is composed of a membrane having multiple pores and is arranged concentrically through the non-porous layer. A pore refers to a communicating pore that extends at least from the inner surface to the outer surface. At the interface between the two porous layers and the non-porous layer, the region consisting of the porous layer and the region consisting of the non-porous layer may slightly overlap each other.

[0024] The total thickness of the two porous layers is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. If the total thickness of the porous layers is above the lower limit, it is easier to ensure the mechanical strength of the hollow fiber membrane. The total thickness of the porous layers is preferably 100 μm or less, more preferably 90 μm or less, and even more preferably 80 μm or less. If the total thickness of the porous layers is below the upper limit, it is possible to suppress the reduction in the amount of membrane filling when modularizing the hollow fiber membrane. The lower and upper limits of the total thickness of the porous layers can be arbitrarily combined, for example, 10 to 100 μm is preferred. The thickness of the porous layer was determined by observing cross-sections perpendicular to the longitudinal direction at five arbitrary locations on the hollow fiber membrane using a scanning electron microscope (SEM), and then analyzing these images to obtain the average thickness of the porous layer.

[0025] The average pore diameter of the multiple pores formed in the porous layer is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.05 μm or more. If the average pore diameter is above the lower limit, it is unlikely to become a significant resistance affecting oxygen permeability. The average pore diameter of the multiple pores formed in the porous layer is preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. If the average pore diameter is below the upper limit, sufficient membrane strength is easily obtained. The lower and upper limits of the average pore diameter can be arbitrarily combined; for example, 0.01 to 5 μm is preferred. The average pore diameter was determined by observing the surface of the porous layer using a scanning electron microscope (SEM), randomly selecting 30 pores, measuring the longest diameter of each pore, and averaging the results.

[0026] The porous layer is preferably composed of one or more materials selected from polyolefin resin, polyurethane resin, and fluororesin, in order to further enhance oxygen permeability. The two porous layers may be made of the same material or different materials. In particular, it is preferable that both porous layers are made of a material containing polyolefin resin.

[0027] Porous layers are formed, for example, by melt stretching. In melt stretching, the resin that will become the material for the porous layer is first heated to a fluid state above its melting point and extruded in a cylindrical shape. Next, the extruded fluid resin is cooled to a non-fluid state and its shape is fixed. After that, the porous structure is formed by stretching the resin with its fixed shape under optimal conditions.

[0028] The thickness of the nonporous layer is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. If the thickness of the nonporous layer is above the lower limit, defects are less likely to occur during manufacturing, and stable production is easier. The thickness of the nonporous layer is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. If the thickness of the nonporous layer is below the upper limit, the decrease in oxygen permeability is easier to suppress. The lower and upper limits of the thickness of the nonporous layer can be arbitrarily combined, for example, 0.3 to 10 μm is preferred. The thickness of the non-porous layer was determined by observing cross-sections perpendicular to the longitudinal direction at five arbitrary locations on the hollow fiber membrane using a scanning electron microscope (SEM), and then analyzing these images to obtain the average thickness of the non-porous layer.

[0029] The material constituting the non-porous layer is preferably polystyrene resin or polyolefin resin, more preferably polyolefin resin, even more preferably polyethylene resin, and particularly preferably low-density polyethylene. By making the non-porous layer a material containing one or more of the above resins, it becomes possible to increase the overall mechanical strength of the hollow fiber membrane while ensuring sufficient oxygen permeability. The non-porous layer may consist of one material or two or more materials.

[0030] The outer diameter of the hollow fiber membrane 11 is preferably 1 mm or less, and more preferably 0.8 mm or less. If the outer diameter of the hollow fiber membrane 11 is below the upper limit, it is possible to suppress the reduction in the amount of hollow fiber membrane packed when forming a membrane module. The outer diameter of the hollow fiber membrane 11 is preferably 0.05 mm or more, and more preferably 0.1 mm or more. If the outer diameter of the hollow fiber membrane 11 is above the lower limit, it is possible to secure a sufficient inner diameter of the hollow section, thereby reducing the effect of the oxygen flow rate through the hollow section decreasing due to pressure loss, etc. The lower and upper limits of the outer diameter of the hollow fiber membrane 11 can be arbitrarily combined, for example, 0.05 to 1 mm is preferred. The outer diameter of the hollow fiber membrane is defined as the diameter of the smallest circle inscribed within the outer edge of the cross-section when the hollow fiber membrane is cut by any plane perpendicular to its longitudinal direction. This is determined as the average value measured at any three to ten locations.

[0031] The method for manufacturing hollow fiber membranes is not particularly limited, and known methods can be used. For example, a hollow fiber membrane, which is a single-layer membrane consisting of a non-porous layer, can be obtained by melt-spinning a resin using a composite nozzle die, while appropriately adjusting the extrusion speed and winding speed, and then cooling and solidifying it in an unstretched state. The hollow fiber membrane obtained by spinning may be subjected to constant-length heat treatment (annealing). When polyethylene is used, the constant-length heat treatment is preferably performed at 105 to 130°C for 8 to 16 hours.

[0032] When manufacturing a hollow fiber membrane consisting of a multilayer film including a porous layer, after constant length heat treatment, the material forming the porous layer is stretched at a stretching temperature below the Vicat softening point. The stretching can be a single-stage stretch, a two-stage stretch in which cold stretching is followed by hot stretching, or a multi-stage stretch in which cold stretching is followed by hot stretching divided into two or more stages. The temperature for cold stretching is preferably within the range of 0°C to a temperature lower than the Vicat softening point - 20°C. The stretching ratio can be set as appropriate, for example, from 2 to 5 times.

[0033] The materials for the first gas passage pipe 12 and the second gas passage pipe 14 are preferably those that have excellent mechanical strength and durability, such as polycarbonate, polysulfone, polyolefin, PVC (polyvinyl chloride), acrylic resin, ABS resin, and modified PPE (polyphenylene ether). The materials for the first gas passage pipe 12 and the second gas passage pipe 14 may be one type or two or more types.

[0034] The first end 12a of the first gas passage pipe 12 is provided with a gas supply port 20 that connects to the internal flow path 13. The second support column 18 is tubular, and its interior is a flow path 19 that communicates with the flow path 15 of the second gas passage pipe 14. A gas outlet 22 is provided at the second end 12b of the first gas passage pipe 12 to which the second support column 18 is connected, and a flow path 21 is formed connecting the flow path 19 of the second support column 18 and the gas outlet 22. Inside the first gas passage pipe 12, the flow path 13 and the flow path 21 are separated, so that gas (air) does not flow directly from the flow path 13 to the flow path 21.

[0035] In the hollow fiber membrane element 1, the flow paths 13, 15, 19, 21 and the hollow fiber membrane 11 form a series of gas flow passages. A gas supply means 31 is connected to the gas supply port 20, which is the inlet of the gas flow passage, via a gas supply pipe 24. A compressor capable of adjusting the pressure of the supplied gas is preferred as the gas supply means 31. The gas supply pipe 24 is provided with a gas supply amount control means 30 for controlling the amount of gas supplied to the gas supply port 20. The gas supply amount control means 30 can be any device capable of controlling the gas supply amount, such as a solenoid valve or a valve. A gas discharge pipe 26 is connected to the gas outlet 22, which is the outlet of the gas flow passage. The gas discharge pipe 26 is equipped with a gas flow rate adjustment means 32 that adjusts the flow rate of gas discharged from the gas outlet 22. The gas flow rate adjustment means 32 can be any device that can control the amount of gas discharged, such as a solenoid valve or a valve. A pressure gauge 34 is provided in the gas discharge pipe 26 between the gas outlet 22 and the gas flow rate adjustment means 32.

[0036] The gas supplied to the gas passage from the gas supply port 20 is supplied to the hollow portion of each hollow fiber membrane 11 from the flow path 13 of the first gas passage pipe 12. A portion of the gas supplied to each hollow fiber membrane 11 permeates to the outside of the membrane. The remaining gas that did not permeate the hollow fiber membrane 11 enters the flow path 15 of the second gas passage pipe 14, passes through the flow path 19 inside the second support column 18, and is discharged from the upper gas outlet 22. The open / closed state of the gas supply amount control means 30 or the gas flow rate adjustment means 32 may be adjusted manually or by a control panel via a solenoid valve. When a control panel and solenoid valve are used, the adjustment can be made automatically while monitoring the site conditions from a distance.

[0037] In this example configuration, the second support column 18 serves both the function of supporting the hollow fiber membrane element and the function of gas discharge. This is preferable because it makes it easier to make the water treatment device more compact. The ratio r / R of the inner diameter r (mm) to the outer diameter R (mm) of the second support column 18 is preferably 0.50 to 0.70, and more preferably 0.51 to 0.60. If the ratio r / R is within the above range, the strength of the second support column 18 will be sufficiently high.

[0038] The length of the second support column 18 should be designed according to the water supply amount, etc. For example, 1 to 3 m is preferable, and 1.2 to 2.5 m is more preferable. If the length of the second support column 18 is greater than or equal to the lower limit, the hollow fiber membrane element will be sufficiently large, and a sufficient membrane area will be secured. This avoids the situation where more hollow fiber membrane elements must be installed in each membrane module in order to meet the required membrane area. Therefore, the processability and cost of the membrane module will be unfavorable.

[0039] The form of the second support column 18 is not particularly limited, and examples include a square tube shape, a cylindrical shape, etc. The material of the second support column 18 is not particularly limited, and examples include stainless steel (SUS).

[0040] The first support column 16 may be tubular or solid columnar. The material of the first support column 16 is not particularly limited, and examples include stainless steel (SUS).

[0041] The method for manufacturing the hollow fiber membrane element 1 is not particularly limited, and examples include a method comprising the following steps (a) to (e). Step (a): The first and second ends of multiple hollow fiber membranes 11 bundled into a sheet are inserted into potting cases, potting resin is injected and hardened to fix the hollow fiber membrane sheet to the potting case. Step (b): The tip of the potting case on which the hollow fiber membrane 11 is fixed is cut to obtain a hollow fiber membrane sheet 10. Step (c): Connect the first support column 16 and the second support column 18 to the first end 12a and the second end 12b of the first gas passage pipe 12. Step (d): Connect the first support column 16 and the second support column 18 to the first end 14a and the second end 14b of the second gas passage pipe 14. Step (e): Insert the upper end of the hollow fiber membrane sheet 10 into the first gas passage pipe 12 and fix it in place with a potting section, and insert the lower end of the hollow fiber membrane sheet 10 into the second gas passage pipe 14 and fix it in place with a potting section.

[0042] [Hollow fiber membrane unit] Figure 4 is a perspective view showing a hollow fiber membrane unit 100 according to an example of an embodiment. The hollow fiber membrane unit 100 comprises a plurality of hollow fiber membrane elements 1. The number of hollow fiber membrane elements 1 in the hollow fiber membrane unit 100 can be set as appropriate, for example, to 2 to 30.

[0043] In the hollow fiber membrane unit 100, the gas supply pipes 24 connected to the gas supply port 20 of each hollow fiber membrane element 1 are independent of each other, and the gas discharge pipes 26 connected to the gas discharge port 22 of each hollow fiber membrane element 1 are independent of each other. In one hollow fiber membrane unit 100, multiple gas supply pipes 24 are connected collectively to a single gas supply means 31. The hollow fiber membrane unit 100 has a simple structure in which multiple hollow fiber membrane elements 1 are not interconnected, making the manufacturing process less complicated. Furthermore, design changes are easy, such as changing the number of hollow fiber membrane elements 1 or changing the height position of each hollow fiber membrane element 1.

[0044] [Methods for dispersing air] The aeration means 4 is a device that injects gas into the water to be treated W from a number of holes, generating a group of rising bubbles. A blower 41 is connected to the aeration means 4 via an aeration gas flow rate adjustment means 40. The aeration gas flow rate adjustment means 40 adjusts the flow rate of gas supplied from the blower 41 to the aeration means 4. Examples of the aeration gas flow rate adjustment means 40 include solenoid valves and valves. The aeration means 4 is located below the hollow fiber membrane unit 100 and has the function of circulating the water to be treated in the treatment tank and of removing the microbial layer formed on the surface of the hollow fiber membrane 11 by utilizing the rise of the bubble group. As the aeration means 4, known aeration devices such as single-pipe aeration devices or siphon aeration devices can be used. The gas supplied to the aeration means 4 is air containing nitrogen. From the viewpoint of making the anaerobic treatment area on the outer side of the microbial layer formed on the surface of the hollow fiber membrane 11 more anaerobic, a gas with a high nitrogen content may be used.

[0045] [Control means] The control means 35 adjusts either or both of the flow rate of gas discharged from the gas outlet 22, which is the outlet of the gas flow passage (exhaust gas flow rate), and the pressure of gas supplied to the gas supply port 20, which is the inlet of the gas flow passage (supply gas pressure). For example, the exhaust gas flow rate is controlled by adjusting the opening of the gas flow rate adjustment means 32 so that the pressure measured by the pressure gauge 34 reaches a predetermined value. For example, the supply gas pressure is controlled by adjusting the discharge pressure of the gas supply means 31 so that the pressure measured by the pressure gauge 34 reaches a predetermined value.

[0046] ≪Water Treatment Methods≫ In the water treatment method according to this embodiment, treated water is obtained by purifying the water to be treated W containing ammonia nitrogen. Below, as an example of the water treatment method according to this embodiment, a water treatment method using the water treatment apparatus 200 will be described. The water treatment method in this example includes a normal operation step in which a hollow fiber membrane element 1 is immersed in the water to be treated and air is circulated through the gas flow passage of the hollow fiber membrane element 1 to form a microbial layer on the surface of the hollow fiber membrane 11, and a microbial layer peeling step in which air is supplied to the gas flow passage from the other end while one of the inlet and outlet of the gas flow passage is sealed, thereby peeling the microbial layer from the surface of the hollow fiber membrane 11.

[0047] (Normal operation process) As shown in Figure 1, a hollow fiber membrane unit 100 and an aeration means 4 are installed in the treatment tank 110, and the water to be treated W is introduced into the treatment tank 110. At this time, the treatment tank 110 is filled with the water to be treated W so that the hollow fiber membrane unit 100 and the aeration means 4 placed in the treatment tank 110 are immersed in the water to be treated W. In this state, air is supplied from the gas supply means 31 to the gas flow passage of each hollow fiber membrane element 1 through the gas supply pipe 24.

[0048] Oxygen in the air supplied to each hollow fiber membrane element 1 permeates more easily from the inner surface to the surface of each hollow fiber membrane 11 compared to nitrogen. In the initial stages of water treatment, microorganisms and bacteria present in the water to be treated W adhere to the surface of each hollow fiber membrane 11, forming a microbial layer derived from microorganisms or bacteria. Microorganisms or bacteria may be grown in activated sludge already used in another water treatment plant, etc., and the hollow fiber membrane element 1 may be immersed in this mixture at a predetermined concentration to pre-form a microbial layer derived from microorganisms or bacteria on the surface of the hollow fiber membrane 11. Activated sludge has various component compositions and proportions depending on the type of water to be treated, but it can be used that has been grown by feeding on BOD (organic matter) components and nutrients (nitrogen, phosphorus, etc.) contained in the water to be treated.

[0049] By continuously supplying air to the hollow fiber membrane element 1, the oxygen that permeates through each hollow fiber membrane 11 dissolves and diffuses within the microbial layer, forming an oxygen gradient (concentration) in the direction of the microbial layer's film thickness. As a result, the inner layer of the microbial layer becomes an oxygen-rich aerobic state, while the outer layer becomes an anaerobic state with reduced oxygen. Consequently, the microbial layer develops an aerobic treatment region on the inner side and an anaerobic treatment region on the outer side. In the aerobic treatment area, ammonia contained in the water to be treated is oxidized by aerobic treatment (BOD oxidation) and converted to nitrate. In the anaerobic treatment area, the nitrate produced in the aerobic treatment area is treated as nitrogen by anaerobic treatment (BOD oxidation) and denitrified. In this way, both aerobic and anaerobic treatment are carried out in a single process within the treatment tank 110.

[0050] In a normal operation process, the air supplied from the gas supply port 20 to the gas flow passage of the hollow fiber membrane element 1 has its oxygen consumed by the hollow fiber membrane 11, and the remaining gas, which has a lower oxygen concentration than the air, is discharged from the gas outlet 22. As a result, the pressure of the air passing through the gas flow passage is lower at the outlet than at the inlet. The pressure measured by the pressure gauge 34 installed in the gas discharge pipe 26 is taken as the outlet pressure of the gas flow passage during normal operation. The outlet pressure of the gas flow passage can be adjusted by changing the amount of gas supplied to the gas flow passage by changing either or both of the opening of the gas supply amount control means 30 and the opening of the gas flow rate adjustment means 32. In normal operation, the outlet pressure of the gas flow passage is preferably maintained within the range of 10 to 40 kPa, and more preferably within the range of 20 to 30 kPa, for example, in gauge pressure. If the outlet pressure is above the lower limit of the above range, sufficient oxygen necessary for the microbial layer can be supplied. If it is below the upper limit, the load on the gas supply means 31 is reduced, and the risk of failure is reduced.

[0051] During normal operation, the microbial layer on the surface of the hollow fiber membrane 11 grows over time. When the microbial layer adheres excessively to the surface of the hollow fiber membrane 11, a bridging phenomenon occurs where adjacent membranes connect to each other. This reduces the effective membrane area and thus the effective surface area of ​​the biofilm. Furthermore, due to reduced contact between raw water and biofilm, aerobic treatment on the inner and anaerobic sides of the microbial layer does not occur at all for the wastewater to be treated. As a result, the wastewater does not come into contact with the biofilm and is discharged directly from the treatment tank via a so-called shortcut (a short path for raw water occurs). This reduces the aerobic and anaerobic treatment reactions, and the water quality of the treated water purified during normal operation deteriorates. Furthermore, when bridging occurs, even if aeration washing is performed, the bubbles cannot reach the membrane spaces, and the excess biofilm accumulation layer (i.e., bridging) cannot be reduced. Therefore, in order to suppress the deterioration of the treated water quality, the following microbial layer removal process is performed.

[0052] (Microbial layer removal process) In the microbial layer peeling process, while continuing to supply air to the gas flow passage, the gas flow rate adjustment means 32 is closed to reduce the flow rate of gas discharged from the gas outlet 22 to zero (start of the microbial layer peeling process). When air is supplied from the inlet of the gas passage with the outlet sealed in this manner, the gas (air or residual gas) inside the hollow fiber membrane 11 is pushed out from the membrane wall of the hollow fiber membrane 11. As a result, a gas layer is formed between the microbial layer attached to the surface of the hollow fiber membrane 11 and the surface of the hollow fiber membrane 11, causing the microbial layer to detach from the surface of the hollow fiber membrane 11.

[0053] With the gas flow rate adjustment means 32 closed, the pressure measured by the pressure gauge 34 installed in the gas discharge pipe 26 is taken as the internal pressure of the gas flow passage in the microbial layer peeling process. In other words, when the microbial layer peeling process is performed, the internal pressure and the outlet pressure are the same. Furthermore, the pressure measured by the pressure gauge 34 immediately before sealing the outlet of the gas flow passage (outlet pressure) is defined as the outlet pressure at the end of the normal operation process. In other words, during the normal operation process, the internal pressure and the outlet pressure are not the same. At the start of the microbial layer peeling process, it is preferable to close the gas flow rate adjustment means 32 and increase the pressure (discharge pressure) of the gas supplied from the gas supply means 31 to further increase the internal pressure of the gas passage. A higher internal pressure in the gas passage makes it easier to peel off the microbial layer from the surface of the hollow fiber membrane 11.

[0054] The internal pressure of the gas flow passage in the microbial layer detachment process is preferably equal to or greater than the outlet pressure in the normal operation process, and more preferably 1.5 times or more the outlet pressure. If the outlet pressure is not constant in the normal operation process, the internal pressure in the microbial layer detachment process is preferably 1 time or more, and more preferably 1.5 times or more, the outlet pressure at the end of the normal operation process. The internal pressure of the gas flow passage in the microbial layer removal process is preferably set according to the conditions of the water treatment site. For example, it is preferable to maintain it within the range of 15 to 60 kPa in gauge pressure, and more preferably within the range of 30 to 50 kPa. If the outlet pressure is above the lower limit of the above range, the effect of the microbial layer removal process is sufficiently obtained, and if it is below the upper limit, the load on the gas supply means 31 is reduced, and the risk of failure is reduced.

[0055] After the microbial layer peeling process is carried out until a predetermined processing time is reached, the gas flow rate adjustment means 32 is opened and gas discharge from the gas outlet 22 is started (stopping the microbial layer peeling process). After that, the normal operation process is carried out again. In the microbial layer peeling step, a portion of the microbial layer attached to the surface of the hollow fiber membrane 11 may be peeled off, or all of it may be peeled off. The processing time from the start to the stop of the microbial layer peeling step is preferably 10 to 60 minutes, more preferably 20 to 50 minutes, and even more preferably 30 to 40 minutes. If the processing time is above the lower limit of the above range, the effect of the microbial layer peeling step is sufficiently obtained, and if it is below the upper limit, the load on the gas supply means 31 is reduced, and the risk of failure is reduced.

[0056] (Aeration process) During the purification treatment of the water to be treated W, it is preferable to include a step (aeration step) in which a group of bubbles are sent from the aeration means 4 to perform aeration as needed. It is preferable to perform aeration at least during the microbial layer removal process. Aeration may be performed both during the normal operation process and during the microbial layer removal process. The aeration during the microbial layer removal process may be stronger (gas flow rate higher) than the aeration during the normal operation process. Air is preferred as the gas supplied to the aeration means 4.

[0057] In particular, performing an aeration process during the microbial layer peeling process is preferable because it makes it easier to remove the microbial layer peeled off from the surface of the hollow fiber membrane 11. In the aeration process, the bubble clusters may be continuously supplied from the aeration means 4, or intermittently supplied. When discharging a group of bubbles from the aeration means 4, the flow rate of the gas supplied to the aeration means 4 may be constant or may change over time.

[0058] (Control process) It is preferable to include a control step that measures the water quality of the treated water in the treatment tank 110 after the start of the normal operation process and initiates the microbial layer removal process based on the water quality. Examples of measurement parameters that serve as indicators of treated water quality include ammonia nitrogen concentration, BOD (biochemical oxygen demand), COD (chemical oxygen demand), and nitrate concentration. It is preferable to measure one or more of these parameters. Known methods can be used to measure each parameter. For example, ammonia nitrogen concentration can be measured using a known ammonia sensor.

[0059] In the control process, for example, measurement data obtained by periodically measuring the water quality of the treated water is sent to the control means 35, and the microbial layer peeling process is started based on the measurement data. Preferably, when the water quality of the treated water falls below a preset level, the gas flow rate adjustment means 32 is closed to start the microbial layer removal process, and the discharge pressure of the gas supply means 31 is adjusted so that the internal pressure measured by the pressure gauge 34 reaches a predetermined value. The microbial layer peeling process can also be stopped and the normal operation process can be restarted using the control means 35. For example, after a predetermined processing time has elapsed since the start of the microbial layer peeling process, the gas flow rate adjustment means 32 is opened to stop the microbial layer peeling process, and the discharge pressure of the gas supply means 31 and the opening of the gas flow rate adjustment means 32 are adjusted so that the outlet pressure measured by the pressure gauge 34 reaches a predetermined value, and the normal operation process is started.

[0060] In the water treatment method of this embodiment, first, a normal operation process is performed, and if the water quality of the treated water deteriorates, a microbial layer removal process is performed, and then the normal operation process is repeated. Once treated water of the desired quality is obtained, the microbial layer removal process is performed last. After that, sludge containing the removed microbial layer is recovered by using a solid-liquid separation method such as a separation membrane (not shown), and treated water with the treated water W purified is obtained.

[0061] When the water treatment device 200 has multiple hollow fiber membrane units 100, it is preferable to configure control means so that the start and stop of the microbial layer removal process and the start of the normal operation process can be controlled for each unit. In this case, there may be a period between the start and end of the water treatment when some of the multiple hollow fiber membrane units 100 perform the normal operation process and the remaining hollow fiber membrane units 100 perform the microbial layer removal process.

[0062] As described above, in the present invention, the microbial layer can be detached by forming an air layer between the surface of the hollow fiber membrane and the microbial layer attached thereto. Therefore, bridging can be prevented from occurring in the hollow fiber membrane element, and even if bridging occurs, the microbial layer can be detached and the water treatment capacity can be restored.

[0063] The present invention is not limited to the embodiments described above. For example, in the microbial layer removal process of the embodiment, the outlet of the gas flow passage was sealed and air was supplied from the inlet, but a configuration in which the inlet of the gas flow passage is sealed and air is supplied from the outlet is also possible. The configuration of the hollow fiber membrane element 1 only needs to include a gas flow passage for circulating gas in the hollow portion of the hollow fiber membrane, and can be modified as appropriate.

[0064] The water treatment method of the present invention is not limited to a method using a hollow fiber membrane unit 100 equipped with a hollow fiber membrane element 1. For example, each hollow fiber membrane element 1 may be configured to control the start and stop of the microbial layer removal process and the start of the normal operation process.

[0065] Furthermore, it is possible to replace the components in the above embodiments with well-known components as appropriate, without departing from the spirit of the present invention, and the above-described modifications may be combined as appropriate. [Examples]

[0066] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0067] <Example 1> The water treatment device 200 illustrated in Figure 1 was used to purify the water to be treated W. The hollow fiber membrane element 1 has the configuration shown in Figures 2 and 3, and the membrane area S is 30 m². 2 They used what is. Step 1: The hollow fiber membrane element 1 was immersed in the water to be treated W, and the gauge pressure (outlet pressure) of the pressure gauge 34 was maintained at 20 kPa while the normal operation process was carried out to prepare the hollow fiber membrane element 1 on which a microbial layer had formed. The hollow fiber membrane element 1 was withdrawn from the water to be treated, its mass M1 in a wet state was measured, and it was returned to the water to be treated. Step 2: Next, the gas flow rate adjustment means 32 was closed, the discharge pressure of the gas supply means 31 was increased, and the gauge pressure (internal pressure) of the pressure gauge 34 was maintained at 40 kPa, and the microbial layer peeling process was carried out for 30 minutes. After that, while maintaining the gas supply from the gas supply means 31, aeration was performed for 10 minutes, and then the hollow fiber membrane element 1 was lifted from the treated water and its mass M2 in the wet state was measured. Evaluation: The amount of microbial layer removed per membrane area M' (unit: g / m²) is calculated using the following formula (1). 2 The value of the microbial layer removal amount M' was calculated. A larger value indicates a better microbial layer removal effect. M'=(M1-M2) / S...Equation (1) In this case, during mass measurement in a "wet state," water droplets may adhere to the surface of the hollow fiber membrane element 1 on which the microbial layer is formed, but the mass is measured in a state where the water droplets do not fall off.

[0068] <Example 2> Step 1 is the same as in Example 1. Except for maintaining the gauge pressure (internal pressure) of the pressure gauge 34 at 20 kPa in Step 2, the microbial layer peeling process was performed in the same manner as in Example 1, and the mass M2 was measured and evaluated.

[0069] <Comparative Example 1> Step 1 is the same as in Example 1. In Step 2, the gas flow rate adjustment means 32 was not sealed, and the gauge pressure (outlet pressure) of the pressure gauge 34 was maintained at 20 kPa for 30 minutes. After that, while maintaining the gas supply from the gas supply means 31, aeration was performed for 10 minutes, and then the hollow fiber membrane element 1 was removed from the treated water, and the mass M2 was measured and evaluated in the same manner as in Example 1.

[0070] [Table 1]

[0071] As shown in the results in Table 1, in Examples 1 and 2, where air was supplied to the gas passage (the hollow portion of the hollow fiber membrane) while the gas passage was sealed to eliminate gas emissions from the passage, a greater amount of the microbial layer attached to the surface of the hollow fiber membrane was removed compared to Comparative Example 1, where the gas passage was not sealed. Furthermore, compared to Example 2, where the internal pressure of the gas flow passage (gauge pressure of pressure gauge 34) in the microbial layer peeling process was 1 times that of the outlet pressure (gauge pressure of pressure gauge 34) in the normal operation process, Example 1, where the internal pressure was 2 times that of the outlet pressure (gauge pressure of pressure gauge 34), showed a significantly larger amount of microbial layer removal. [Explanation of symbols]

[0072] 1. Hollow fiber membrane element 4. Aeration means 10 Hollow fiber membrane sheet 11. Hollow fiber membrane (gas flow channel) 12. First gas passage piping 13. Flow path (gas flow path) 14. Second gas passage piping 15 Flow path (gas flow path) 16 1st pillar 18 Second pillar 19 Flow path (gas flow path) 20 Gas supply ports 21 Flow path (gas flow path) 22 Gas outlet 24 Gas supply piping 26 Gas discharge piping 30 Gas supply amount control means 32 Gas flow rate adjustment means 34 Pressure gauge 31 Gas supply means 35 Control means 40. Aeration gas flow rate adjustment means 41 Blower 100 Hollow fiber membrane units 110 Processing tanks 200 Water Treatment Equipment

Claims

1. A water treatment method for obtaining treated water by purifying water containing ammonia nitrogen, A normal operation process involves immersing a hollow fiber membrane element, which comprises multiple hollow fiber membranes that are gas permeable membranes and has gas flow passages for circulating gas in the hollow portions of the hollow fiber membranes, in the water to be treated, and circulating air through the gas flow passages to form a microbial layer on the surface of the hollow fiber membranes, The process includes, after the normal operation step, a microbial layer peeling step in which the microbial layer is peeled off from the surface of the hollow fiber membrane. A water treatment method comprising the microbial layer removal step, wherein one of the inlet and outlet of the gas flow passage is sealed, and air is supplied to the gas flow passage from the other.

2. The water treatment method according to claim 1, wherein the internal pressure of the gas flow passage in the microbial layer peeling step is 1.5 times or more the outlet pressure of the gas flow passage in the normal operation step.

3. The water treatment method according to claim 1 or 2, further comprising a control step of initiating the microbial layer peeling step based on the water quality of the treated water.

4. Multiple hollow fiber membrane units, each comprising multiple hollow fiber membrane elements, are immersed in the water to be treated. The water treatment method according to claim 1 or 2, wherein a portion of the plurality of hollow fiber membrane units performs the normal operation step and the remainder performs the microbial layer peeling step during a period of time.

5. A water treatment apparatus that purifies water to be treated containing ammonia nitrogen to obtain treated water, A hollow fiber membrane element comprising multiple hollow fiber membranes which are gas permeable membranes, and having a gas flow passage for circulating gas in the hollow portion of the hollow fiber membranes, A means for dispersing air is provided below the hollow fiber membrane element, A gas supply means for supplying gas to the aforementioned gas flow passage, A gas flow rate adjustment means for adjusting the flow rate of gas discharged from the gas flow passage, A water treatment apparatus comprising: a control means for adjusting the opening degree of the gas flow rate adjustment means based on the water quality of the treated water.

6. The water treatment apparatus according to claim 5, wherein the control means adjusts the opening of the gas flow rate adjustment means and the discharge pressure of the gas supply means based on the water quality of the treated water.

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