WATER TREATMENT METHODS, HOLLOW FIBER MEMBRANES, HOLLOW FIBER MEMBRANE COMPONENTS, AND WATER TREATMENT EQUIPMENT

Abstract

The aim of the invention is to propose a method for treating water with a simple structure and capable of efficiently discharging condensate from the hollow fiber membrane of each hollow fiber membrane element. The wastewater treatment method using a hollow fiber membrane unit consists of multiple hollow fiber membrane elements and includes the following steps: supplying oxygen-containing gas to each hollow fiber membrane element within the multiple hollow fiber membrane elements immersed in the water to be treated; allowing oxygen-containing gas to permeate from the inside out of the multiple hollow fiber membranes constituting the multiple hollow fiber membrane elements and forming a microbial layer on the surface of each hollow fiber membrane; discharging the condensate generated in the hollow fiber membranes along with the excess oxygen-containing gas that does not permeate through the hollow fiber membranes; and individually controlling the amount of excess gas discharged from each hollow fiber membrane element within the multiple hollow fiber membrane elements.

Description

Water treatment method, hollow fiber membrane element, hollow fiber membrane unit, and water treatment device

[0001] The present invention relates to a water treatment method, a hollow fiber membrane element, a hollow fiber membrane unit, and a water treatment device. This application claims priority to Japanese Patent Application No. 2023-180050, filed on October 19, 2023, the contents of which are incorporated herein by reference.

[0002] Raw water for purification, such as river water or groundwater, or wastewater is treated to remove organic matter and the like. In particular, it is known that industrial wastewater and domestic wastewater are treated to remove organic matter and the like before being reused as industrial water or discharged into rivers, etc. As a water treatment method, a bioreactor known as a membrane aeration biofilm reactor (MABR) has been proposed, in which a microbial layer (biofilm) derived from microorganisms in the wastewater is formed on the surface of a gas-permeable hollow fiber membrane and oxygen is supplied to the microbial layer from the inner surface of the hollow fiber membrane.

[0003] In MABR, for example, a hollow fiber membrane unit including a plurality of hollow fiber membrane elements, each of which is formed by assembling a plurality of hollow fiber membranes into a sheet and connected to gas pipes above and below, is immersed in wastewater, which is the water to be treated. Even when the gas supplied to each hollow fiber membrane element is sufficiently dehumidified, water vapor that permeates the wastewater through the membrane and enters the hollow fiber membrane, or water vapor contained in the gas (oxygen, air, etc.) supplied to the hollow fiber membrane element, may condense, producing water (condensed water) inside the hollow fiber membrane. The presence of water inside the hollow fiber membrane reduces the oxygen permeability coefficient of the hollow fiber membrane and the effective membrane area, leading to a decrease in operating efficiency.

[0004] Patent Document 1 discloses a membrane module that includes an upper manifold connected to the upper headers of a plurality of hollow fiber membrane elements and a lower manifold connected to the lower headers of the elements, and that joins the water inside the hollow fiber membranes of the hollow fiber membrane elements in the lower manifold and discharges the water through a discharge pipe.

[0005] International Publication No. 2019 / 159667

[0006] However, conventional membrane modules such as those described in Patent Document 1 have a complex structure, including the provision of upper and lower manifolds connected to multiple hollow fiber membrane elements, which makes the manufacturing process cumbersome and disadvantageous in terms of cost. Furthermore, the amount of condensed water generated inside the hollow fiber membranes of each hollow fiber membrane element varies, but because the discharge of condensed water cannot be controlled individually for each hollow fiber membrane element, it is difficult to efficiently discharge condensed water from the hollow fiber membranes of all hollow fiber membrane elements, resulting in low operational efficiency of wastewater treatment.

[0007] An object of the present invention is to provide a water treatment method that has a simple structure and that can efficiently discharge condensed water from within the hollow fiber membranes of each hollow fiber membrane element, as well as a hollow fiber membrane element and hollow fiber membrane unit that can be suitably used in the water treatment method.

[0008] In view of the above problems, the inventors have discovered that by adopting a method for individually controlling the discharge of condensed water generated within each hollow fiber membrane element and a structure equipped with condensed water discharge mechanisms that communicate with the gas passage pipes at the top and bottom of the hollow fiber membrane element, it is possible to efficiently discharge condensed water within the hollow fiber membranes of each hollow fiber membrane element, and have completed the present invention.

[0009] The present invention includes the following features: [1] A water treatment method using a hollow fiber membrane unit comprising a plurality of hollow fiber membrane elements, comprising: supplying an oxygen-containing gas to each of a plurality of hollow fiber membrane elements immersed in water to be treated; permeating the oxygen-containing gas from inside to outside of a plurality of hollow fiber membranes constituting the plurality of hollow fiber membrane elements to form a microbial layer on the surface of each of the hollow fiber membranes; discharging condensed water generated within each of the hollow fiber membranes together with residual gas of the oxygen-containing gas that did not permeate the hollow fiber membrane; and individually controlling the discharge amount of the residual gas discharged from each of the plurality of hollow fiber membrane elements. [2] The hollow fiber membrane element comprises a plurality of hollow fiber membranes which are gas permeable membranes, a first gas passage pipe, a second gas passage pipe, and a condensed water discharge mechanism, and is provided with a gas supply port and a gas discharge port for supplying an oxygen-containing gas, wherein each of the hollow fiber membranes is arranged so that its length direction is vertical, wherein the first gas passage pipe is a pipe through which the oxygen-containing gas supplied from the gas supply port flows, and is arranged so as to extend horizontally while being connected to the upper ends of the plurality of hollow fiber membranes, and wherein the second gas passage pipe is a pipe through which the remaining gas of the oxygen-containing gas which has not permeated the hollow fiber membranes flows, and is arranged so as to extend horizontally while being connected to the lower ends of the plurality of hollow fiber membranes, and wherein the condensed water discharge mechanism is a tubular member and is arranged parallel to the hollow fiber membranes with both ends connected to the first gas passage pipe and the second gas passage pipe, a gas outlet for discharging condensed water generated inside the hollow fiber membranes together with the residual gas through the circulation path, the gas outlet being provided at an upper portion of the hollow fiber membrane element; ...[4] The water treatment method according to any one of [1] to [3], wherein a microbial layer derived from microorganisms or bacteria in the water to be treated is formed on the surface of the plurality of hollow fiber membranes. [5] A hollow fiber membrane element comprising a plurality of hollow fiber membranes which are gas permeable membranes, a first gas passage pipe, a second gas passage pipe, and a condensed water discharge mechanism, and provided with a gas supply port and a gas discharge port for supplying an oxygen-containing gas, and immersed in water to be treated, wherein the plurality of hollow fiber membranes are arranged so that their length direction is vertical, the first gas passage pipe is a pipe through which the oxygen-containing gas supplied from the gas supply port flows, and is arranged so as to extend horizontally while connected to the upper ends of the plurality of hollow fiber membranes, the second gas passage pipe is a pipe through which the remaining gas of the oxygen-containing gas which has not permeated the hollow fiber membranes flows, and is arranged so as to extend horizontally while connected to the lower ends of the hollow fiber membranes, and the condensed water discharge mechanism is a tubular member and is arranged parallel to the hollow fiber membranes with both ends connected to the first gas passage pipe and the second gas passage pipe, a hollow fiber membrane element, wherein the interior of the first gas passage pipe, the interior of the plurality of hollow fiber membranes, the interior of the second gas passage pipe, and the interior of the condensed water discharge mechanism are connected in this order to form a circulation path, and the gas outlet for discharging condensed water generated inside the plurality of hollow fiber membranes together with the residual gas through the circulation path is provided in an upper part of the hollow fiber membrane element. [6] The hollow fiber membrane element according to claim 5, wherein the condensed water discharge mechanism is a hollow support. [7] The hollow fiber membrane element according to [5] or [6], wherein one end of a gas discharge pipe is connected to the gas outlet, and the other end of the gas discharge pipe is disposed above the liquid level. [8] The hollow fiber membrane element according to [6], wherein the ratio r / R of the inner diameter r (mm) of the support to the outer diameter R (mm) of the support is 0.50 to 0.70. [9] The hollow fiber membrane element according to any of [5] to [8], further comprising a gas supply amount control means for controlling the amount of the oxygen-containing gas supplied to the gas supply port.

[10] The hollow fiber membrane element according to any one of [5] to [9], further comprising a gas discharge control means for controlling the discharge of the residual gas from the gas discharge port.

[11] A hollow fiber membrane element according to any one of [5] to

[10] , wherein a microbial layer derived from microorganisms or bacteria is formed on the surface of the hollow fiber membrane.

[12] A hollow fiber membrane unit comprising a plurality of hollow fiber membrane elements according to any one of [5] to

[11] , wherein the gas supply paths to the gas supply ports of each of the hollow fiber membrane elements are independent, and the gas discharge paths from the gas discharge ports of each of the hollow fiber membrane elements are independent.

[13] A water treatment device comprising one or more hollow fiber membrane units according to

[12] .

[0010] According to the present invention, there are provided a water treatment method which has a simple structure and can efficiently discharge condensed water from within the hollow fiber membranes of each hollow fiber membrane element, as well as a hollow fiber membrane element, a hollow fiber membrane unit, and a water treatment device which can be suitably used in the water treatment method.

[0011] Fig. 1 is a perspective view showing a hollow fiber membrane element according to an example of an embodiment. Fig. 2 is a front view of the hollow fiber membrane element of Fig. 1. Fig. 3 is a perspective view showing a hollow fiber membrane unit according to an example of an embodiment. Fig. 4 is a schematic view showing how a water treatment method according to an example of an embodiment is performed. Fig. 5 is a graph showing the relationship between the flow rate of residual gas in a condensed water discharge mechanism and the lift height of condensed water in an experimental example.

[0012] In this specification and claims, when a numerical range is indicated using "to", the numerical range includes the numerical values ​​before and after "to" as the lower and upper limits. For example, "A to B" means A or more and B or less.

[0013] The water treatment method according to the embodiment is a water treatment method using a hollow fiber membrane unit comprising a plurality of hollow fiber membrane elements, and includes the following steps (i) to (iv): (i) supplying an oxygen-containing gas to each of a plurality of hollow fiber membrane elements immersed in water to be treated; (ii) causing the oxygen-containing gas to permeate from the inside to the outside of the hollow fiber membranes constituting the plurality of hollow fiber membrane elements, thereby forming a microbial layer on the surface of each of the hollow fiber membranes; (iii) discharging condensed water generated within each of the hollow fiber membranes together with residual gas of the oxygen-containing gas that did not permeate the hollow fiber membrane; and (iv) individually controlling the amount of residual gas discharged from each of the plurality of hollow fiber membrane elements.

[0014] The water to be treated by the water treatment method according to the embodiment typically includes, but is not limited to, wastewater such as industrial wastewater and domestic wastewater. For example, raw water such as river water and groundwater may also be used as the water to be treated.

[0015] [Hollow fiber membrane element] First, a hollow fiber membrane element that can be suitably used in the water treatment method according to the embodiment will be described with reference to the drawings. Note that the dimensions and the like shown in the drawings in the following description are merely examples, and the present invention is not necessarily limited thereto. Appropriate changes can be made within the scope of the present invention.

[0016] Fig. 1 is a perspective view showing a hollow fiber membrane element 1 according to one embodiment. Fig. 2 is a front view of the hollow fiber membrane element 1. The hollow fiber membrane element 1 includes a hollow fiber membrane sheet 10 made up of a plurality of hollow fiber membranes 11, a first gas passage pipe 12, a second gas passage pipe 14, a support mechanism 16, and a condensed water discharge mechanism 18.

[0017] In the hollow fiber membrane element 1, the first gas passage pipe 12 is on the upper side and the second gas passage pipe 14 is on the lower side, and the first gas passage pipe 12 and the second gas passage pipe 14 are arranged to extend horizontally. Both ends of a support mechanism 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 a condensed water discharge mechanism 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.

[0018] The support mechanism 16 is not particularly limited as long as it has the function of supporting the first gas passage pipe 12 and the second gas passage pipe 14. Examples of the support mechanism 16 include hollow pillars and solid pillars.

[0019] The condensed water discharge mechanism 18 is not particularly limited as long as the inside of the condensed water discharge mechanism 18 is in communication with the inside of the first gas passage pipe 12 and the inside of the second gas passage pipe 14, respectively, and has the function of discharging condensed water from the hollow fiber membranes of the hollow fiber membrane element. As the condensed water discharge mechanism 18, a tubular member can be used, for example, a hollow support or a hollow tube.

[0020] If the condensed water discharge mechanism 18 also has the function of supporting the first gas passage piping 12 and the second gas passage piping 14, the stability of the hollow fiber membrane element 1 will be improved. From this viewpoint, a hollow support is preferred as the condensed water discharge mechanism 18. Furthermore, when the condensed water discharge mechanism 18 also has the function of supporting the first gas passage piping 12 and the second gas passage piping 14, from the viewpoint of further simplifying the structure of the hollow fiber membrane element 1, an embodiment in which only a hollow support is provided as the condensed water discharge mechanism 18 without providing a support mechanism 16 is also preferred.

[0021] 1 shows an example in which both the support mechanism 16 and the condensed water discharge mechanism 18 are hollow pillars. In this example, the first gas passage pipe 12 and the second gas passage pipe 14 are supported by the support mechanism 16 and the condensed water discharge mechanism 18, which extend vertically, to form a rectangular frame shape.

[0022] The hollow fiber membrane sheet 10 is formed by arranging a plurality of hollow fiber membranes 11 in a sheet shape, and is arranged between the support mechanism 16 and the condensed water discharge mechanism 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. The length direction of each hollow fiber membrane 11 is vertical and parallel to the support mechanism 16 and the condensed water discharge mechanism 18. Support by the support mechanism 16 and the condensed water discharge mechanism 18 maintains a constant distance between the first gas passage pipe 12 and the second gas passage pipe 14, thereby forming a flat hollow fiber membrane element 1 in which the surface shape of the hollow fiber membrane sheet 10 is maintained. Note that the hollow fiber membrane element 1 is not limited to a flat type and can be formed into, for example, a cylindrical or rectangular tube shape.

[0023] The upper end of each hollow fiber membrane 11 is attached to the first gas passage pipe 12 so that the interior 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 so that the interior of the hollow fiber membrane 11 communicates with the flow path 15 inside the second gas passage pipe 14. The manner in which the upper ends of each hollow fiber membrane 11 are attached to the first gas passage pipe 12 is not particularly limited, and any known manner can be used, such as fixing each hollow fiber membrane 11 to the first gas passage pipe 12 with a potting resin, with the upper end face of each hollow fiber membrane 11 open inside the first gas passage pipe 12. The same applies to the manner in which the lower ends of each hollow fiber membrane 11 are attached to the second gas passage pipe 14. That is, for example, one embodiment is one in which the lower end surface of each hollow fiber membrane 11 is open inside the second gas passage pipe 14, and the lower end of each hollow fiber membrane 11 is fixed to the first gas passage pipe 12 with potting resin.

[0024] Examples of potting resins include epoxy resins, unsaturated polyester resins, polyurethane resins, silicone-based fillers, and various hot-melt resins. The potting resins forming the potting portion may be one type or two or more types.

[0025] The number of hollow fiber membranes 11 constituting the hollow fiber membrane sheet material 10 is not particularly limited and can be, for example, 10,000 to 50,000. The hollow fiber membrane sheet material 10 may be composed of a single sheet made up of a plurality of hollow fiber membranes 11, or may be composed of a laminate in which a plurality of sheets made up of a plurality of hollow fiber membranes 11 are stacked.

[0026] A hollow fiber gas-permeable membrane used in water treatment by MABR, i.e., a gas-permeable membrane for water treatment, on whose surface a microbial layer derived from microorganisms or bacteria in the water to be treated is formed, can be used as the hollow fiber membrane 11. More specifically, a hollow fiber membrane that can allow oxygen to permeate from the inner surface to the surface by supplying oxygen to the hollow portion can be used, and a hollow fiber membrane including a non-porous layer, which will be described later, is preferred.

[0027] The shape of the hollow fiber membrane 11 is not particularly limited, and can be, for example, a substantially cylindrical shape. However, the term "substantially cylindrical" means that the shape of any cross section perpendicular to the longitudinal direction is a three-dimensional shape such as a perfect circle, an egg, an oval, an ellipse, or the like.

[0028] The hollow fiber membrane 11 may be a single-layer membrane or a multi-layer membrane. An example of a hollow fiber membrane made of a single layer is a hollow fiber membrane made of a non-porous layer. An example of a hollow fiber membrane made of a multi-layer membrane is a three-layer hollow fiber membrane in which a non-porous layer is disposed between two porous layers. Each of the two porous layers is made of a membrane having a plurality of pores, and is concentrically disposed via the non-porous layer. The pores refer to holes that communicate at least from the inner surface to the surface. At the interface between the two porous and non-porous layers, the region made of the porous layer and the region made of the non-porous layer may slightly interpenetrate each other.

[0029] 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. When the total thickness of the porous layers is equal to or greater than the aforementioned lower limit, the mechanical strength of the hollow fiber membrane is easily ensured. 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. When the total thickness of the porous layers is equal to or less than the aforementioned upper limit, a reduction in the membrane packing amount when modularizing the hollow fiber membrane can be suppressed. 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, 15 to 90 μm is more preferred, and 20 to 80 μm is more preferred. The thickness of the porous layer was determined by observing a cross section perpendicular to the longitudinal direction at any five locations of the hollow fiber membrane using a scanning electron microscope (SEM) and analyzing the images to determine the average thickness of the porous layer measured.

[0030] 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 equal to or greater than the lower limit, it is unlikely to act as a resistance that affects oxygen permeation. 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 equal to or less than the upper limit, sufficient membrane strength is likely to be obtained. The lower and upper limits of the average pore diameter can be arbitrarily combined, and for example, 0.01 to 5 μm is preferred, 0.03 to 4 μm is more preferred, and 0.05 to 3 μm is even more preferred. The average pore diameter is a value obtained by observing the surface portion of the porous layer using a SEM, randomly selecting 30 pores, measuring the longest diameter of each pore, and averaging the results.

[0031] The material constituting the porous layer preferably contains one or more selected from polyolefin resin, polyurethane resin, and fluororesin in order to further increase oxygen permeability. The two porous layers may be made of the same material or different materials. In particular, it is preferable that both of the two porous layers are made of a material containing a polyolefin resin.

[0032] The porous layer is formed, for example, by a melt-stretching method. In the melt-stretching method, the resin that will be the material for the porous layer is first heated to a fluid state above its melting point and then extruded into a cylindrical shape. Next, the extruded fluid resin is cooled to a non-fluid state and the shape is fixed. The fixed-shape resin is then stretched under optimal conditions to form the porous structure.

[0033] The thickness of the non-porous 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 non-porous layer is equal to or greater than the above-mentioned lower limit, defects are less likely to occur during production, facilitating stable production. The thickness of the non-porous 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 non-porous layer is equal to or less than the above-mentioned upper limit, it is easier to suppress a decrease in oxygen permeability. The lower and upper limits of the thickness of the non-porous layer can be arbitrarily combined, and for example, 0.3 to 10 μm is preferable, 0.5 to 8 μm is more preferable, and 1 to 6 μm is more preferable. The thickness of the non-porous layer is determined by observing cross sections perpendicular to the longitudinal direction at any five points of the hollow fiber membrane with a scanning electron microscope (SEM), analyzing the images, and calculating the average thickness of the non-porous layer measured.

[0034] The material constituting the non-porous layer is preferably a polystyrene resin or a polyolefin resin, more preferably a polyolefin resin, even more preferably a polyethylene resin, and particularly preferably low-density polyethylene. By making the non-porous layer from a material containing one or more of the above resins, it is possible to increase the mechanical strength of the entire hollow fiber membrane while ensuring sufficient oxygen permeability. The material constituting the non-porous layer may be one type or two or more types.

[0035] The outer diameter of the hollow fiber membrane 11 is preferably 1 mm or less, more preferably 0.8 mm or less. If the outer diameter of the hollow fiber membrane 11 is equal to or less than the above-mentioned upper limit, it is possible to prevent the filling amount of the hollow fiber membrane from becoming small when the membrane is assembled into a membrane module. The outer diameter of the hollow fiber membrane 11 is preferably 0.05 mm or more, more preferably 0.1 mm or more. If the outer diameter of the hollow fiber membrane 11 is equal to or greater than the above-mentioned lower limit, it is possible to ensure a sufficient inner diameter of the hollow portion, thereby reducing the effect of a decrease in the flow rate of oxygen flowing through the hollow portion 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 preferable, and 0.1 to 0.8 μm is more preferable. The outer diameter of the hollow fiber membrane refers to the diameter of the smallest circle inscribed on the outer edge of the cut surface when the hollow fiber membrane is cut along any plane perpendicular to the longitudinal direction of the hollow fiber membrane, and is calculated as the average value measured at any three to ten locations.

[0036] The method for producing a hollow fiber membrane 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 the unstretched membrane. The hollow fiber membrane obtained by spinning may be subjected to a fixed-length heat treatment (annealing treatment). When polyethylene is used, the fixed-length heat treatment is preferably performed at 105 to 130°C for 8 to 16 hours.

[0037] When producing a hollow fiber membrane consisting of a multilayer membrane including a porous layer, after the fixed-length heat treatment, the membrane is stretched at a stretching temperature below the Vicat softening point of the material forming the porous layer. The stretching may be a one-stage stretching, a two-stage stretching in which cold stretching is followed by hot stretching, or a multi-stage stretching in which cold stretching is followed by hot stretching in two or more stages. The cold stretching temperature is preferably within a range from 0°C to a temperature lower than the Vicat softening point -20 (°C). The stretching ratio can be set appropriately, for example, to 2 to 5 times.

[0038] The first gas passage pipe 12 and the second gas passage pipe 14 are preferably made of a material having excellent mechanical strength and durability, such as polycarbonate, polysulfone, polyolefin, PVC (polyvinyl chloride), acrylic resin, ABS resin, modified PPE (polyphenylene ether), etc. The first gas passage pipe 12 and the second gas passage pipe 14 may be made of one type of material or two or more types of material.

[0039] A first end 12a of the first gas passage piping 12 is provided with a gas supply port 20 connected to the internal flow path 13. The condensed water discharge mechanism 18 is a tubular member, and its interior forms a flow path 19 that communicates with the flow path 15 of the second gas passage piping 14. A gas discharge port 22 is provided at a second end 12b of the first gas passage piping 12 to which the condensed water discharge mechanism 18 is connected, and a flow path 21 is formed that connects the flow path 19 of the condensed water discharge mechanism 18 to the gas discharge port 22. Inside the first gas passage piping 12, the flow path 13 and the flow path 21 are separated, so that the oxygen-containing gas does not flow directly from the flow path 13 to the flow path 21.

[0040] In this way, in the hollow fiber membrane element 1, the interior of the first gas passage piping 12, the interiors of the plurality of hollow fiber membranes 11, the interior of the second gas passage piping 14, and the interior of the condensed water discharge mechanism 18 are all connected in this order to form a flow path 23, and a gas discharge port 22 is provided at the top. The flow path 23 is a path that connects the flow path 13 of the first gas passage piping 12, the interior of each hollow fiber membrane 11, the flow path 15 of the second gas passage piping 14, and the flow path 19 in the condensed water discharge mechanism 18 in this order. Gas supplied from the gas supply port 20 is supplied from the flow path 13 of the first gas passage piping 12 to the inside of each hollow fiber membrane 11. A portion of the oxygen-containing gas supplied to each hollow fiber membrane 11 permeates out of the hollow fiber membrane 11. The remaining gas that does not permeate the hollow fiber membrane 11 enters the flow path 15 of the second gas passage piping 14, passes through the flow path 19 in the condensed water discharge mechanism 18, and passes through the flow path 21 of the first gas passage piping 12 before being discharged from the upper gas discharge port 22. In this way, the condensed water discharge mechanism 18 has the functions of supporting the hollow fiber membrane element, discharging gas, and draining condensed water, so there is no need to install separate gas discharge mechanisms and condensed water discharge mechanisms. This makes it possible to create a compact and simple water treatment device composed of hollow fiber membrane units.

[0041] In water treatment using the hollow fiber membrane element 1, water vapor that has permeated the hollow fiber membranes 11 from the water to be treated and infiltrated therein, or water vapor contained in the oxygen-containing gas, may condense, resulting in condensed water inside the hollow fiber membranes 11. However, in the hollow fiber membrane element 1, by increasing the supply rate of oxygen-containing gas, the force of the residual gas pushing out the condensed water increases, and the condensed water can be discharged to the outside of the hollow fiber membrane element 1 together with the residual gas.

[0042] The ratio r / R of the inner diameter r (mm) to the outer diameter R (mm) of the condensed water drain mechanism 18 is preferably 0.50 to 0.70, and more preferably 0.51 to 0.60. If the ratio r / R is within this range, the strength of the condensed water drain mechanism 18 will be sufficiently high.

[0043] The length of the condensed water discharge mechanism 18 may be designed depending on the amount of water supplied, etc. For example, 1.0 to 3.0 m is preferable, and 1.2 to 2.5 m is more preferable. If the length of the condensed water discharge mechanism 18 is equal to or greater than the lower limit, the hollow fiber membrane element becomes sufficiently large, ensuring a sufficient membrane area. This avoids the need to install more hollow fiber membrane elements in each membrane module in order to satisfy the required membrane area. This provides advantages in terms of the workability and cost of the membrane module. If the length of the condensed water discharge mechanism 18 is equal to or less than the upper limit, condensed water can be easily discharged via the condensed water discharge mechanism 18.

[0044] The shape of the condensed water drain mechanism 18 is not particularly limited, and examples thereof include a square tube shape, a cylindrical shape, etc. The material of the condensed water drain mechanism 18 is not particularly limited, and examples thereof include stainless steel (SUS).

[0045] The support mechanism 16 may be tubular or may be a solid columnar shape. The material of the support mechanism 16 is not particularly limited, and examples thereof include stainless steel (SUS).

[0046] A gas supply pipe 24 is connected to the gas supply port 20 provided in the first gas passage pipe 12. The gas supply pipe 24 is provided with a gas supply amount control means 30 that controls the amount of oxygen-containing gas supplied to the gas supply port 20. The gas supply amount control means 30 may be any means that can control the amount of oxygen-containing gas supplied, and examples of the gas supply amount control means 30 include a solenoid valve and a valve.

[0047] A gas exhaust pipe 26 is connected to the gas exhaust port 22 provided in the first gas passage pipe 12. In water treatment using the hollow fiber membrane element 1, the hollow fiber membrane element 1 is immersed in the water to be treated, but it is preferable that the other end of the gas exhaust pipe 26 opposite to the one end connected to the gas exhaust port 22 is positioned above the liquid level so that the remaining gas and condensed water are discharged above the liquid level. This makes it possible to prevent activated sludge in the wastewater from entering and clogging the gas exhaust pipe 26 when the water to be treated is wastewater.

[0048] The gas exhaust pipe 26 is provided with a gas exhaust amount control means 32 that controls the amount of residual gas exhausted from the gas exhaust port 22. The gas exhaust amount control means 32 may be any means that can control the amount of residual gas exhausted, and examples thereof include a solenoid valve and a valve.

[0049] A pressure gauge 34 may be provided in the gas exhaust pipe 26. As the amount of condensed water generated inside the hollow fiber membrane 11 increases, the pressure in the path from the condensed water discharge mechanism 18 to the gas exhaust pipe 26 decreases. Therefore, by providing the pressure gauge 34 in the gas exhaust pipe 26 and monitoring the pressure during water treatment, the amount of condensed water present inside the hollow fiber membrane 11 can be ascertained to some extent.

[0050] Specifically, when the pressure value measured by the pressure gauge 34 falls below a preset pressure value, the aperture of the gas supply amount control means 30 or the gas discharge amount control means 32 is increased to increase the supply amount of oxygen-containing gas, thereby increasing the flow rate of the residual gas discharged from the hollow fiber membrane 11 via the second gas passage piping 14 and the condensed water discharge mechanism 18, making it easier to discharge condensed water together with the residual gas. On the other hand, when the pressure value measured by the pressure gauge 34 exceeds a preset pressure value, the aperture of the gas supply amount control means 30 or the gas discharge amount control means 32 is decreased to reduce the supply amount of oxygen-containing gas, thereby reducing the flow rate of the residual gas discharged from the hollow fiber membrane 11 via the second gas passage piping 14 and the condensed water discharge mechanism 18, thereby discharging the condensed water and residual gas and reducing energy consumption.

[0051] The open / close state of the gas supply amount control means 30 or the gas discharge amount control means 32 may be adjusted manually or via a control panel through a solenoid valve. When a control panel and solenoid valve are used, automatic adjustments can be made while monitoring the on-site situation from a distance. As described above, by adjusting the open / close state of the gas supply amount control means 30 or the gas discharge amount control means 32, it is possible to control the discharge state of condensed water while also reducing energy consumption.

[0052] The method for manufacturing the hollow fiber membrane element 1 is not particularly limited, and examples thereof include a method including the following steps (a) to (e). Step (a): Inserting the first and second ends of a plurality of hollow fiber membranes 11 bundled into a sheet into potting cases, respectively, and injecting and curing potting resin to fix the hollow fiber membrane sheet to the potting case. Step (b): Cutting the tip of the potting case with the hollow fiber membranes 11 fixed therein to obtain the hollow fiber membrane sheet 10. Step (c): Connecting the support mechanism 16 and the condensed water discharge mechanism 18 to the first end 12a and the second end 12b of the first gas passage pipe 12. Step (d): Connecting the support mechanism 16 and the condensed water discharge mechanism 18 to the first end 14a and the second end 14b of the second gas passage pipe 14. Step (e): The upper end of the hollow fiber membrane sheet 10 is inserted into the first gas passage pipe 12 and fixed with a potting portion, and the lower end of the hollow fiber membrane sheet 10 is inserted into the second gas passage pipe 14 and fixed with a potting portion.

[0053] [Hollow fiber membrane unit] Figure 3 is a perspective view showing a hollow fiber membrane unit 100 according to one example of the embodiment. The hollow fiber membrane unit 100 includes a plurality of hollow fiber membrane elements 1. The number of hollow fiber membrane elements 1 included in the hollow fiber membrane unit 100 can be set appropriately, and can be, for example, 2 to 30.

[0054] In the hollow fiber membrane unit 100, the gas supply pipes 24 (gas supply paths) connected to the gas supply ports 20 of each hollow fiber membrane element 1 are independent of each other, and the gas exhaust pipes 26 (gas exhaust paths) connected to the gas exhaust ports 22 of each hollow fiber membrane element 1 are independent of each other. The hollow fiber membrane unit 100 has a simple structure in which multiple hollow fiber membrane elements 1 are not interconnected, eliminating the need for additional large pipes for collecting condensed water and reducing the complexity of the manufacturing process. Furthermore, design changes, such as changing the number of hollow fiber membrane elements 1 or the heightwise position of each hollow fiber membrane element 1, are easy. Furthermore, because the hollow fiber membrane element 1 utilizes the interior of the condensed water discharge mechanism 18 as a path for discharging residual gas and condensed water, the amount of piping for discharging residual gas and condensed water can be reduced, further simplifying the structure.

[0055] Furthermore, in the hollow fiber membrane unit 100, the gas supply path and gas discharge path for each hollow fiber membrane element 1 are independent, making it easy to grasp the amount of condensed water in the hollow fiber membranes 11 of each hollow fiber membrane element 1, and it is possible to independently control the flow rate of the residual gas according to the condition of each hollow fiber membrane element 1. Therefore, it is possible to individually set conditions for discharging the condensed water in the hollow fiber membranes 11 according to the level of condensed water in each hollow fiber membrane element 1, and it is possible to prevent a decrease in operating efficiency due to a decrease in the oxygen permeability coefficient of the hollow fiber membranes 11 and a decrease in the effective membrane area.

[0056] In this way, in the hollow fiber membrane unit 100, condensed water can be efficiently discharged from each hollow fiber membrane element 1, and the force used to discharge the residual gas can be used to discharge the condensed water together, thereby saving energy.

[0057] [Water Treatment Device] The water treatment device according to the embodiment is a device including one or more hollow fiber membrane units according to the embodiment. The water treatment device according to the embodiment can adopt any known aspect other than including the hollow fiber membrane unit according to the embodiment described above.

[0058] [Water Treatment Method] A wastewater treatment method using a hollow fiber membrane unit 100 will be described below as an example of a water treatment method according to the embodiment. The water treatment method using the hollow fiber membrane unit 100 includes the following steps. Gas supply step: An oxygen-containing gas is supplied to each of a plurality of hollow fiber membrane elements 1 immersed in water to be treated. Reaction step: The oxygen-containing gas is permeated from inside to outside of the plurality of hollow fiber membranes 11 constituting the plurality of hollow fiber membrane elements 1, forming a microbial layer on the surface of each hollow fiber membrane 11. Discharge step: Condensed water generated inside the hollow fiber membranes 11 is discharged together with residual gas that did not permeate the hollow fiber membranes 11 of the oxygen-containing gas. Control step: The discharge amount of residual gas discharged from each of the plurality of hollow fiber membrane elements 1 is individually controlled. A more detailed description will be given below, taking as an example a case where wastewater is treated as the water to be treated.

[0059] 4, hollow fiber membrane units 100 are installed in a treatment tank 110, and wastewater W, which serves as the water to be treated, is introduced into the treatment tank 110. At this time, the treatment tank 110 is filled with wastewater W so that the hollow fiber membrane units 100 placed in the treatment tank 110 are immersed in the wastewater W. In this state, an oxygen-containing gas is supplied to each hollow fiber membrane element 1 from a blower (not shown) through gas supply piping 24.

[0060] (Reaction Step) The oxygen-containing gas supplied to each hollow fiber membrane element 1 permeates from the inner surface of each hollow fiber membrane 11 to the membrane surface. In the initial stage of wastewater treatment, microorganisms, bacteria, etc. present in the wastewater W adhere to the surface of each hollow fiber membrane 11, forming a microbial layer derived from the microorganisms or bacteria. Activated sludge already used in another wastewater treatment plant, etc., may be used as a seed to grow microorganisms or bacteria, and the hollow fiber membrane element 1 may be immersed in the resulting solution to a predetermined concentration, thereby forming a microbial layer derived from the microorganisms or bacteria on the surface of the hollow fiber membrane 11 in advance. Activated sludge has various component compositions and ratios depending on the type of wastewater, but activated sludge that has grown using nutrients such as BOD (organic matter), nitrogen, and phosphorus contained in the wastewater as food can be used.

[0061] By continuously supplying oxygen or air to the hollow fiber membrane element 1, oxygen that has permeated each hollow fiber membrane 11 dissolves and diffuses within the microbial layer, forming an oxygen gradient (concentration) across the membrane thickness of the microbial layer. The inner layer of the microbial layer is then in an oxygen-rich aerobic state, while the outer layer is in an oxygen-reduced anaerobic state. This results in an aerobic treatment zone being formed on the inner layer side of the microbial layer, and an anaerobic treatment zone being formed on the outer layer side. In the aerobic treatment zone, ammonia contained in the wastewater is oxidized to nitrate through aerobic treatment (BOD oxidation). In the anaerobic treatment zone, nitrate produced in the aerobic treatment zone is converted to nitrogen through anaerobic treatment (BOD oxidation), resulting in denitrification. In this way, both aerobic treatment and anaerobic treatment are carried out in a single process within the treatment tank 110.

[0062] Although atmospheric air may be supplied to each hollow fiber membrane 11 of the hollow fiber membrane element 1, it is preferable to supply pure oxygen. Supplying highly pure oxygen tends to ensure a sufficient concentration of oxygen dissolved and diffused in the microbial layer, improving wastewater treatment capacity. Using atmospheric air is preferable in terms of reducing running costs. For example, a gas in which the component composition ratio of atmospheric air has been changed by separation or concentration may be supplied to the hollow fiber membrane element 1 in accordance with the characteristics of the wastewater to be treated.

[0063] The thickness of the microbial layer is not particularly limited, and can be adjusted to a thickness that allows optimal aerobic and anaerobic treatment, for example, by performing an operation such as air bubbling cleaning when the microbial layer reaches a predetermined thickness or a predetermined treatment time.

[0064] (Storage Step) The water treatment method according to the embodiment may include a storage step of storing condensed water generated inside the hollow fiber membranes 11 in the hollow fiber membrane element 1 as a step prior to the discharge step.

[0065] During wastewater treatment, in each hollow fiber membrane element 1, water vapor that has permeated the hollow fiber membranes 11 from the wastewater and infiltrated therein, as well as water vapor contained in the oxygen-containing gas, condenses, producing condensed water inside the hollow fiber membranes 11. As the amount of condensed water produced inside the hollow fiber membranes 11 increases, the oxygen permeability coefficient of the hollow fiber membranes 11 decreases, and the effective membrane area decreases, resulting in a decrease in operating efficiency. However, when the amount of condensed water is not significant, the condensed water can be retained within the hollow fiber membrane element 1. The second gas passage pipe at the bottom of the hollow fiber membrane element 1 has the function of storing condensed water, but the discharge step does not necessarily follow the storage step.

[0066] (Discharge process) When the pressure gauge 34 detects that the pressure of the residual gas in the condensed water discharge mechanism 18 and the gas discharge piping 26 has dropped to a predetermined value, the gas supply amount control means 30 increases the supply amount of oxygen-containing gas, thereby increasing the flow rate of the residual gas discharged from the hollow fiber membrane 11 via the second gas passage piping 14 and the condensed water discharge mechanism 18, and discharging the condensed water together with the residual gas from the hollow fiber membrane element 1.

[0067] (Control step) By controlling the discharge amount of residual gas discharged from a plurality of hollow fiber membrane elements 1, it is possible to control the implementation of a storage step in which condensed water is retained within the hollow fiber membrane element 1 and the implementation of a discharge step in which condensed water is discharged together with residual gas. Furthermore, in the control step, the discharge amount of residual gas discharged from a plurality of hollow fiber membrane elements 1 is individually controlled. This allows the storage step and the discharge step to be carried out separately in each hollow fiber membrane element 1, depending on the amount of condensed water produced by each hollow fiber membrane element 1.

[0068] The flow velocity of the residual gas in the condensed water discharge mechanism 18 during the discharge step is preferably 0.3 to 8 m / s, more preferably 1 to 6 m / s, and even more preferably 1.5 to 2.5 m / s. If the flow velocity of the residual gas is within the above range, the condensed water can rise to a height of 1.5 m or more in the condensed water discharge mechanism, allowing the condensed water to be efficiently discharged together with the residual gas to the outside of the hollow fiber membrane element 1. If the flow velocity of the residual gas is above the lower limit, the condensed water is likely to rise to a high height in the condensed water discharge mechanism, making this method more applicable to large elements than small elements. On the other hand, if the flow velocity of the residual gas is below the upper limit, it is easy to suppress the generation of excessive energy required to increase the condensed water in the condensed water discharge mechanism.

[0069] The flow rate of the residual gas in the condensed water discharge mechanism 18 can be adjusted by adjusting the supply rate (L / min) of the oxygen-containing gas to the hollow fiber membrane element 1 and the inner diameter r (mm) of the condensed water discharge mechanism 18. The flow rate (m / s) of the residual gas is obtained by the following formula: v=V Ｇ / S where the symbols in the formula have the following meanings: v: flow rate of residual gas (m / s) V Ｇ : Amount of air supplied to the hollow fiber membrane element (L / min) S: Cross-sectional area of ​​the hollow part of the condensed water drainage mechanism (mm ２ )

[0070] After the wastewater treatment, the microbial layer is peeled off from the hollow fiber membrane 11, for example, by a bubbling process. Then, a solid-liquid separation method using a separation membrane (not shown) or the like is used to recover sludge containing the peeled off microbial layer, thereby completing the wastewater treatment.

[0071] As described above, in the present invention, the hollow fiber membrane unit has a simple structure, and the conditions for discharging condensed water can be controlled individually for each hollow fiber membrane element, allowing for efficient discharge of condensed water from the hollow fiber membranes of each hollow fiber membrane element.

[0072] The present invention is not limited to the above-described embodiment. For example, although the gas supply port 20 is provided at the top of the hollow fiber membrane element 1, the present invention is not limited to this configuration. For example, a gas supply port that is not connected to the flow path 15 may be provided at the first end 14a of the second gas passage piping 14 in the hollow fiber membrane element 1, and the support mechanism 16 may be a tubular member, such as a hollow support, so that the oxygen-containing gas supplied from the gas supply port is supplied to the hollow fiber membranes 11 via the support mechanism 16 and the first gas passage piping 12.

[0073] The water treatment method of the present invention is not limited to a method using a hollow fiber membrane unit 100 including a hollow fiber membrane element 1. For example, as long as the amount of residual gas discharged from a plurality of hollow fiber membrane elements can be individually controlled, the water treatment method may be a water treatment method using a hollow fiber membrane unit including a plurality of known hollow fiber membrane elements that discharge residual gas without passing through a condensed water discharge mechanism.

[0074] Furthermore, within the scope of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modifications may be combined as appropriate.

[0075] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following descriptions.

[0076] [Experimental Example 1] Five hollow fiber membrane elements were fabricated with the same configuration as the hollow fiber membrane element 1 illustrated in Figure 1, each 3 m high, and each condensed water discharge mechanism was a cylindrical support, with the inner diameter varied. The cross-sectional area for each inner diameter was obtained. The cross-sectional area of ​​the hollow part of each of the five condensed water discharge mechanisms was 12.6 mm. ２ , 19.6 mm ２ , 33.2 mm ２ , 50.2 mm ２ , 132.7 mm ２The amount of air supplied to the hollow fiber membrane element was set to 3 L / min, and the height to which the condensed water rose in each condensed water discharge mechanism was measured. The flow rate (m / s) of the residual gas passing through each condensed water discharge mechanism was calculated from the amount of air supplied (L / min) to the hollow fiber membrane element using the following formula, and the relationship between the flow rate (m / s) of the residual gas in the condensed water discharge mechanism and the lifted height (mm) of the condensed water was investigated. The results are shown in Figure 5. v = V Ｇ / S where the symbols in the formula have the following meanings: v: flow rate of residual gas (m / s) V Ｇ : Amount of air supplied to the hollow fiber membrane element (L / min) S: Cross-sectional area of ​​the hollow part of the condensed water drainage mechanism (mm ２ )

[0077] The results of Figure 5 indicate that if the flow rate of the residual gas in the condensed water discharge mechanism is 0.3 m / s or higher, the condensed water can be lifted 1.5 m or more through the condensed water discharge mechanism, allowing efficient discharge from a 1.5 m-high hollow fiber membrane element. It was also found that if the flow rate of the residual gas in the condensed water discharge mechanism is 1 m / s or higher, the condensed water can be lifted 2.4 m or more through the condensed water discharge mechanism, allowing efficient discharge from a 2.4 m-high hollow fiber membrane element. It was also found that if the flow rate of the residual gas in the condensed water discharge mechanism is 2.5 m / s or higher, the condensed water can be lifted 3.0 m or more through the condensed water discharge mechanism, allowing efficient discharge from a 3.0 m-high hollow fiber membrane element. Furthermore, compared to the air supply rate of 10 L / min to the hollow fiber membrane element in Patent Document 1 (Example 1), the present invention reduces energy consumption by 70%. As described above, compared to conventional technology, a lower air supply rate can be used to achieve both reduced energy consumption during water treatment device operation and condensed water discharge.

[0078] REFERENCE SIGNS LIST 1 hollow fiber membrane element 10 hollow fiber membrane sheet 11 hollow fiber membrane 12 first gas passage pipe 13 flow path 14 second gas passage pipe 15 flow path 16 support mechanism 18 condensed water discharge mechanism 20 gas supply port 22 gas discharge port 23 flow path 24 gas supply pipe 26 gas discharge pipe 30 gas supply amount control means 32 gas discharge amount control means 34 pressure gauge

Claims

1. A water treatment method using a hollow fiber membrane unit having a plurality of hollow fiber membrane elements, comprising: supplying an oxygen-containing gas to each of a plurality of hollow fiber membrane elements immersed in water to be treated; allowing the oxygen-containing gas to permeate from inside to outside of a plurality of hollow fiber membranes constituting the plurality of hollow fiber membrane elements, thereby forming a microbial layer on the surface of each of the hollow fiber membranes; discharging condensed water generated within each of the hollow fiber membranes together with residual gas of the oxygen-containing gas that did not permeate the hollow fiber membrane; and individually controlling the discharge amount of the residual gas discharged from each of the plurality of hollow fiber membrane elements.

2. The hollow fiber membrane element comprises a plurality of hollow fiber membranes which are gas permeable membranes, a first gas passage pipe, a second gas passage pipe, and a condensed water discharge mechanism, and is provided with a gas supply port and a gas discharge port for supplying an oxygen-containing gas, each of the hollow fiber membranes is arranged so that its length direction is vertical, the first gas passage pipe is a pipe for passing the oxygen-containing gas supplied from the gas supply port, and is arranged so as to extend in the horizontal direction while being connected to the upper ends of the plurality of hollow fiber membranes, the second gas passage pipe is a pipe for passing the remaining gas of the oxygen-containing gas which has not permeated the hollow fiber membranes, and is arranged so as to extend in the horizontal direction while being connected to the lower ends of the plurality of hollow fiber membranes, and the condensed water discharge mechanism is a tubular member, and is arranged parallel to the hollow fiber membranes with both ends connected to the first gas passage pipe and the second gas passage pipe, 2. The water treatment method according to claim 1, wherein an interior of the first gas passage pipe, an interior of the plurality of hollow fiber membranes, an interior of the second gas passage pipe, and an interior of the condensed water discharge mechanism are connected in this order to form a circulation path, and the gas discharge port for discharging condensed water generated inside the plurality of hollow fiber membranes together with the residual gas through the circulation path is provided in an upper portion of the hollow fiber membrane element.

3. The water treatment method according to claim 2, wherein the supply amount (L / min) of the oxygen-containing gas to the hollow fiber membrane element and the inner diameter r (mm) of the condensed water drainage mechanism are adjusted so that the flow rate of the residual gas in the condensed water drainage mechanism is 0.3 to 8 m / s.

4. A water treatment method according to claim 1 or 2, in which a microbial layer derived from microorganisms or bacteria in the water to be treated is formed on the surface of the plurality of hollow fiber membranes.

5. A hollow fiber membrane element comprising a plurality of hollow fiber membranes which are gas permeable membranes, a first gas passage pipe, a second gas passage pipe, and a condensed water discharge mechanism, which is provided with a gas supply port and a gas discharge port for supplying an oxygen-containing gas, and which is immersed in water to be treated, wherein the plurality of hollow fiber membranes are arranged so that their length direction is vertical, the first gas passage pipe is a pipe for passing the oxygen-containing gas supplied from the gas supply port, and is arranged so as to extend in the horizontal direction while connected to the upper ends of the plurality of hollow fiber membranes, the second gas passage pipe is a pipe for passing the remaining gas of the oxygen-containing gas which has not permeated the hollow fiber membranes, and is arranged so as to extend in the horizontal direction while connected to the lower ends of the hollow fiber membranes, and the condensed water discharge mechanism is a tubular member, and is arranged parallel to the hollow fiber membranes with both ends connected to the first gas passage pipe and the second gas passage pipe, a circulation path is formed by the interior of the first gas passage pipe, the interior of the plurality of hollow fiber membranes, the interior of the second gas passage pipe, and the interior of the condensed water discharge mechanism being connected in this order, and the gas discharge port for discharging condensed water generated inside the plurality of hollow fiber membranes together with the residual gas through the circulation path is provided in an upper portion of the hollow fiber membrane element.

6. The hollow fiber membrane element according to claim 5, wherein the condensed water drainage mechanism is a hollow support.

7. The hollow fiber membrane element according to claim 5, wherein one end of a gas exhaust pipe is connected to the gas exhaust port, and the other end of the gas exhaust pipe is disposed above the liquid surface.

8. The hollow fiber membrane element according to claim 6, wherein the ratio r / R of the inner diameter r (mm) of the support to the outer diameter R (mm) of the support is 0.50 to 0.

70.

9. The hollow fiber membrane element according to claim 5, further comprising a gas supply amount control means for controlling the amount of said oxygen-containing gas supplied to said gas supply port.

10. The hollow fiber membrane element according to claim 5, further comprising a gas discharge control means for controlling the amount of the residual gas discharged from the gas discharge port.

11. The hollow fiber membrane element according to claim 5, wherein a microbial layer derived from microorganisms or fungi is formed on the surface of the hollow fiber membrane.

12. A hollow fiber membrane unit comprising a plurality of hollow fiber membrane elements according to any one of claims 5 to 11, wherein the gas supply paths to the gas supply ports of each of the hollow fiber membrane elements are independent from each other, and the gas exhaust paths from the gas exhaust ports of each of the hollow fiber membrane elements are independent from each other.

13. A water treatment device comprising one or more hollow fiber membrane units according to claim 12.