Wastewater treatment device and wastewater treatment method

Abstract

To provide a wastewater treatment apparatus and a wastewater treatment method capable of improving a wastewater treatment capacity of MABR.SOLUTION: A wastewater treatment apparatus includes a treatment tank in which wastewater is treated, a hollow fiber membrane module including a hollow fiber membrane, and an air diffuser. The hollow fiber membrane module and the air diffuser are immersed in the wastewater in the treatment tank, and the air diffuser is placed at a position where at least a part thereof does not overlap the hollow fiber membrane module when viewed from above. Using thus configured wastewater treatment apparatus, wastewater treatment is performed using a microbial layer derived from microorganisms in the wastewater formed on a surface of the hollow fiber membrane.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wastewater treatment device and a wastewater treatment method. [Background technology]

[0002] Industrial wastewater and domestic wastewater are treated to remove organic matter and the like from the wastewater before being reused as industrial water or discharged into rivers, etc. Typical methods for treating industrial wastewater and the like include activated sludge treatment, in which the water to be treated is aerated and aerobic microorganisms are used to decompose the organic matter and the like. Such biological water treatment methods, typified by activated sludge treatment, utilize aerobic microorganisms and denitrifying bacteria to remove nitrate nitrogen.

[0003] Conventional activated sludge treatment methods involve the provision of a nitrification tank using aerobic microorganisms and a denitrification tank using anaerobic denitrifying bacteria, with oxygen supplied to the nitrification tank by aeration. However, this treatment method has the problem of requiring large-scale facilities because the nitrification tank and denitrification tank are installed separately. Furthermore, oxygen supply by aeration has limitations on oxygen utilization efficiency, even if the bubble size is reduced, the bubble surface area is increased to improve contact efficiency, or the residence time in the treated water is extended. This results in high running costs.

[0004] To address this issue, a wastewater treatment method using a bioreactor known as a membrane aeration biofilm reactor (MABR) has been proposed (Patent Document 1). This bioreactor forms a microbial layer (biofilm) derived from microorganisms in wastewater on the surface of a hollow fiber membrane, and oxygen is supplied from the inner surface of the hollow fiber membrane. In MABR wastewater treatment, an oxygen gradient is formed in the thickness direction of the microbial layer. Aerobic treatment (BOD oxidation, nitrification of ammonia) occurs on the inner side of the microbial layer, while anaerobic treatment of nitrate (BOD oxidation, denitrification) occurs on the outer side of the microbial layer. Because aerobic and anaerobic treatment can be performed in the same treatment tank, the equipment can be made more compact than conventional treatment methods. Furthermore, because oxygen is supplied from the inner surface of the hollow fiber membrane, oxygen utilization efficiency is higher than with aeration, resulting in reduced running costs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-079335 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to improve the treatment capacity of wastewater treatment using MABR as in Patent Document 1, it is important to be able to efficiently treat the wastewater in the treatment tank. An object of the present invention is to provide a wastewater treatment device and a wastewater treatment method that can improve the wastewater treatment capacity of MABR. [Means for solving the problem]

[0007] The present invention includes the following aspects. [1] A wastewater treatment device that utilizes a microbial layer derived from microorganisms in wastewater formed on the surface of a hollow fiber membrane, The system comprises a treatment tank in which wastewater is treated, a hollow fiber membrane module including hollow fiber membranes, and an aeration device, the hollow fiber membrane module and the aeration device are immersed in the wastewater in the treatment tank, The wastewater treatment device, wherein the air diffuser is disposed at a position where at least a part of the air diffuser does not overlap with the hollow fiber membrane module when viewed from above. [2] The wastewater treatment device according to [1], wherein the air diffuser is disposed at a position lower than the hollow fiber membrane module. [3] The wastewater treatment device according to [1] or [2], comprising a plurality of the hollow fiber membrane modules, and wherein the air diffuser is disposed between any two of the hollow fiber membrane modules when viewed from above. [4] A wastewater treatment method using the wastewater treatment device according to any one of [1] to [3], wherein at least one of the aeration devices is constantly operated to treat the wastewater. [5] The wastewater treatment method according to [4], which includes using a wastewater treatment device equipped with a plurality of the aeration devices and supplying gas at different flow rates to any two of the aeration devices to treat the wastewater. [6] The wastewater treatment method according to [4] or [5], wherein the flow rate B of the gas supplied to the air diffuser is greater than the flow rate A of the gas supplied to the hollow fiber membrane module. [7] The wastewater treatment method according to any one of [4] to [6], wherein the ratio (B / A) of the flow rate B of the gas supplied to the air diffuser to the flow rate A of the gas supplied to the hollow fiber membrane module is 1 to 20. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a wastewater treatment device and a wastewater treatment method that can improve the wastewater treatment capacity of MABR. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing an embodiment of a wastewater treatment device according to the present invention. [Figure 2] FIG. 2 is a schematic view showing another embodiment of the wastewater treatment device according to the present invention. [Figure 3] FIG. 2 is a schematic view showing another embodiment of the wastewater treatment device according to the present invention. [Figure 4] 4 is a schematic diagram showing a state in which gases are supplied at different flow rates to two air diffusers in the wastewater treatment device of FIG. 3. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this specification, when a numerical range is indicated using "to", the numerical values ​​before and after "to" are included as the lower and upper limits.

[0011] [Wastewater treatment equipment] The wastewater treatment device of the present invention is a wastewater treatment device that utilizes a microbial layer derived from microorganisms in wastewater formed on the surface of a hollow fiber membrane, i.e., a wastewater treatment device used for wastewater treatment by MABR. The wastewater treatment device of the present invention includes a treatment tank in which wastewater is treated, a hollow fiber membrane module including hollow fiber membranes, and an aeration device. One or more hollow fiber membrane modules may be arranged in one treatment tank. One or more aeration devices may be arranged in one treatment tank.

[0012] An example of the wastewater treatment device of the present invention will be described below. It should be noted that the dimensions of the figures illustrated in the following description are merely examples, and the present invention is not necessarily limited to them, and can be implemented with appropriate modifications within the scope that does not change the gist of the present invention.

[0013] 1 includes a treatment tank 110, a hollow fiber membrane module 10, and an air diffuser 130. The hollow fiber membrane module 10 and the air diffuser 130 are immersed in wastewater W in the treatment tank 110.

[0014] (treatment tank) The treatment tank 110 contains wastewater W, which is the water to be treated. As the treatment tank 110, any tank conventionally used in this field, such as a large metal container-shaped treatment tank, can be used without any restrictions. Although not shown in detail in FIG. 1, the treatment tank 110 can be connected to a wastewater inlet pipe for containing the wastewater W, which is the water to be treated, inside, and a discharge pipe for discharging the treated water out of the tank after treatment has been completed.

[0015] (Hollow fiber membrane module) The hollow fiber membrane module 10 is generally composed of a housing 12 (upper housing 12A and lower housing 12B) and a hollow fiber membrane sheet 11 in which a plurality of hollow fiber membranes 1 are bundled together in a sheet form. The hollow fiber membranes 1 are the hollow fiber membranes of the present invention described above. The hollow fiber membrane module 10 in this example is arranged in the treatment tank 110 so that the longitudinal direction of the hollow fiber membranes 1 is vertical and so that they are immersed in the wastewater W. This makes it difficult for condensed water (water contained in oxygen, air, etc. and water in the wastewater that has condensed as water inside the membrane) to accumulate inside the hollow fiber membranes 1, and the wastewater treatment capacity can be maintained better.

[0016] The upper housing 12A is a substantially hollow member disposed above the hollow fiber membrane sheet 11. The upper end of the hollow fiber membrane sheet 11 is inserted into the upper housing 12A, and this upper end is fixed to the upper housing 12A with the end faces of each hollow fiber membrane 1 open. The lower housing 12B is a substantially hollow member disposed below the hollow fiber membrane sheet 11. The lower end of the hollow fiber membrane sheet 11 is inserted into the lower housing 12B, and this lower end is fixed to the lower housing 12B with the end faces of each hollow fiber membrane 1 open. This maintains the hollow fiber membrane sheet 11 in a sheet form between the upper housing 12A and the lower housing 12B.

[0017] In the hollow fiber membrane module 10, a pair of support columns are preferably provided to connect both ends of the upper housing 12A and the lower housing 12B. By providing a pair of support columns and maintaining a constant distance between the upper housing 12A and the lower housing 12B, the surface shape of the hollow fiber membrane sheet 11 can be maintained, and a flat hollow fiber membrane module 10 can be constructed. The hollow fiber membrane module 10 is not limited to a flat type, and can also be configured, for example, in a cylindrical or rectangular tubular shape.

[0018] A gas supply line 120 is connected to the upper housing 12A, and oxygen, air, etc. are supplied from a blower (not shown) into the interior of the upper housing 12A. The oxygen, air, etc. sent into the hollow portion of each hollow fiber membrane 1 through the upper housing 12A permeates from the inner surface side to the surface side of each hollow fiber membrane 1.

[0019] The hollow fiber membrane 1 is a hollow fiber membrane used for wastewater treatment by MABR, and is configured so that oxygen can be supplied to the hollow portion and permeate from the inner surface to the surface. During wastewater treatment, a microbial layer derived from microorganisms in the wastewater W is formed on the surface of the hollow fiber membrane 1.

[0020] The shape of the hollow fiber membrane 1 is not particularly limited, and can be, for example, a substantially cylindrical shape. However, "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, egg, oval, ellipse, or the like.

[0021] The hollow fiber membrane 1 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 multilayer 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 composed of a membrane having a plurality of pores, and is disposed concentrically 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 interpenetrate slightly.

[0022] 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 equal to or greater than the 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. If the total thickness of the porous layers is equal to or less than the upper limit, a decrease in the membrane packing amount when modularizing the hollow fiber membranes can be suppressed. The lower and upper limits of the total thickness of the porous layers can be arbitrarily combined, and for example, 10 to 100 μm is preferred. The thickness of the porous layer was determined by observing a cross section perpendicular to the longitudinal direction at any five points of the hollow fiber membrane using a scanning electron microscope (SEM), analyzing the image, and calculating the average thickness of the porous layer.

[0023] The average pore diameter of the 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 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. The average pore diameter was determined by observing the surface of the porous layer using an SEM, randomly selecting 30 pores, measuring the longest diameter of each pore, and averaging the results.

[0024] 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.

[0025] 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.

[0026] 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 lower limit, defects are less likely to occur during production, and stable production is easier. 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 upper limit, a decrease in oxygen permeability is more easily suppressed. The lower and upper limits of the thickness of the non-porous layer can be arbitrarily combined, and for example, 0.01 to 5 μm is preferred. The thickness of the non-porous layer was determined by observing cross sections perpendicular to the longitudinal direction of the hollow fiber membrane at any five points using a scanning electron microscope (SEM), analyzing the images, and calculating the average thickness of the non-porous layer.

[0027] 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 using a material containing one or more of the above resins for the non-porous layer, 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.

[0028] The outer diameter of the hollow fiber membrane 1 is preferably 1 mm or less, more preferably 0.8 mm or less. If the outer diameter of the hollow fiber membrane 1 is equal to or less than the above 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 1 is preferably 0.05 mm or more, more preferably 0.1 mm or more. If the outer diameter of the hollow fiber membrane 1 is equal to or greater than the above 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 1 can be arbitrarily combined, and for example, 0.2 to 1 mm is preferred. The outer diameter of the hollow fiber membrane means 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 3 to 10 points.

[0029] 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.

[0030] 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 the range of 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.

[0031] (aeration device) The air diffuser 130 is a device that sprays gas into the wastewater W. A blower 131 is connected to the air diffuser 130, and the gas supplied from the blower 131 is diffused from the air diffuser 130. The air diffuser 130 is disposed at a position where at least a portion of it does not overlap with the hollow fiber membrane module 10 when viewed from above. The air diffuser 130 of the example shown in Fig. 1 is disposed in the wastewater W so that the entire air diffuser 130 does not overlap with the hollow fiber membrane module 10 when viewed from above.

[0032] When viewed from above, at least a portion of the aeration device 130 does not overlap with the hollow fiber membrane module 10 in the wastewater W, and therefore, an upward flow of the wastewater W is generated highly efficiently above the aeration device 130 by the gas diffused from the aeration device 130. The flow of the rising wastewater W then flows toward the hollow fiber membrane module 10 near the water surface, generating a downward flow, resulting in the circulation of the wastewater W in the treatment tank 110. This makes it possible to prevent the wastewater W introduced into the treatment tank 110 from the wastewater inlet pipe from short-passing and being discharged from the tank from the discharge pipe in an insufficiently treated state. In order to facilitate circulation of the wastewater W in the treatment tank 110, it is preferable to arrange the aeration device 130 in the wastewater W so that the entire aeration device 130 does not overlap with the hollow fiber membrane module 10 when viewed from above, as in this example.

[0033] 1, the air diffuser 130 is disposed at a position lower than the hollow fiber membrane module 10. This makes it easier to circulate the wastewater W in the treatment tank 110 by the upward flow of the wastewater W generated above the air diffuser 130. Note that the air diffuser 130 may be disposed at a position higher than the lower end of the hollow fiber membrane module 10, as long as the wastewater W in the treatment tank 110 can be sufficiently circulated.

[0034] The air diffuser 130 is not particularly limited, and for example, a known air diffuser such as a single-pipe type air diffuser or a siphon type air diffuser can be used. Examples of siphon type air diffusers include those described in International Publication No. 2018 / 155250, Japanese Patent Application Laid-Open No. 2018-202372, Japanese Patent Application Laid-Open No. 2019-76857, and Japanese Patent Application Laid-Open No. 2016-47532.

[0035] [Wastewater treatment method] The wastewater treatment method of the present invention is a method for treating wastewater by using the wastewater treatment device of the present invention and operating at least one air diffuser at all times. However, "operating at least one aeration device at all times" means that one or more aeration devices are always in operation from the start to the end of wastewater treatment, and is not limited to operating a specific aeration device from the start to the end of wastewater treatment. For example, when using a wastewater treatment device equipped with multiple aeration devices, as long as one or more aeration devices are always in operation from the start to the end of wastewater treatment, this may also include a situation in which all of the aeration devices are stopped during treatment.

[0036] Hereinafter, a wastewater treatment method using the above-described wastewater treatment device 100 will be described as an example of the wastewater treatment method of the present invention.

[0037] In the wastewater treatment method of this embodiment, first, wastewater W, which is the water to be treated, is introduced into the treatment tank 110. At this time, the treatment tank 110 is filled with the wastewater W so that the hollow fiber membrane module 10 and the air diffuser 130 arranged in the treatment tank 110 are immersed in the wastewater W. Next, oxygen or air is supplied to the hollow fiber membrane module 10 from a blower (not shown) via a gas supply line 120, thereby causing the oxygen or air to permeate from the hollow portions to the surfaces of the hollow fiber membranes 1. In this embodiment, in such an early stage of wastewater treatment, microorganisms, bacteria, etc. present in the wastewater W adhere to the surface of each hollow fiber membrane 1, forming a microbial layer derived from the microorganisms or bacteria.

[0038] Activated sludge already used in another wastewater treatment plant or the like can be used as a seed to grow microorganisms or bacteria, and the hollow fiber membrane module can be immersed in the resulting solution at a predetermined concentration to form a microbial layer derived from the microorganisms or bacteria on the surface of the hollow fiber membrane 1. Activated sludge has various component compositions and ratios depending on the type of wastewater, but activated sludge that has been grown using the BOD (organic matter) components and nutrients (nitrogen, phosphorus, etc.) contained in the wastewater as food can be used.

[0039] By continuing to supply oxygen or air to the hollow fiber membrane module 10, oxygen that permeates from the hollow portion of each hollow fiber membrane 1 to the surface side dissolves and diffuses within the microbial layer, forming an oxygen gradient (concentration) in the membrane thickness direction of the microbial layer. The inner layer of the microbial layer then becomes an oxygen-rich aerobic state, while the outer layer becomes an oxygen-reduced anaerobic state. As a result, an aerobic treatment region is formed on the inner layer side of the microbial layer, and an anaerobic treatment region is formed on the outer layer side. In the aerobic treatment area, ammonia contained in the wastewater is oxidized to nitrate through aerobic treatment (BOD oxidation). In the anaerobic treatment area, the nitrate produced in the aerobic treatment area is converted to nitrogen through anaerobic treatment (BOD oxidation) and denitrified. In this way, both aerobic treatment and anaerobic treatment are carried out in a single process within the treatment tank 110.

[0040] Although atmospheric air may be supplied to each hollow fiber membrane 1 of the hollow fiber membrane module 10, it is preferable to supply pure oxygen. Supplying highly pure oxygen tends to ensure that the oxygen concentration dissolved and diffused in the microbial layer is sufficient, improving wastewater treatment capacity. Using atmospheric air is preferable in terms of reducing running costs. The hollow fiber membrane module 10 may also be supplied with a gas in which the component composition ratio of atmospheric air has been changed by separation or concentration, for example, to suit the characteristics of the wastewater to be treated. The pressure of the gas (oxygen or air) supplied to each hollow fiber membrane 1 is not particularly limited, but is preferably 200 kPa or less in order to easily prevent damage to components due to oversupply. In order to obtain a wastewater treatment effect sufficient for practical use, the pressure of the gas supplied to each hollow fiber membrane 1 may be, for example, 5 kPa or more.

[0041] 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.

[0042] 1, during wastewater treatment, air is diffused from the air diffuser 130, generating an upward flow in the wastewater W above the air diffuser 130 and circulating the wastewater W in the treatment tank 110. This makes it less likely for the wastewater W introduced into the treatment tank 110 to short-pass, improving the wastewater treatment capacity of the MABR.

[0043] The gas diffused from the air diffuser 130 is not particularly limited as long as it can circulate the wastewater W, and examples thereof include air, nitrogen, and air with an increased nitrogen concentration (high-nitrogen concentration gas). Of these, nitrogen or a high-nitrogen concentration gas is preferred because it makes it easier for the anaerobic treatment region on the exterior side of the microbial layer formed on the surface of the hollow fiber membrane to become anaerobic.

[0044] It is preferable that the flow rate B of the gas supplied to the air diffuser 130 be greater than the flow rate A of the gas supplied to the hollow fiber membrane module 10, since this makes it easier to perform highly efficient wastewater treatment by utilizing the microbial layer on the surface of the hollow fiber membrane while sufficiently circulating the wastewater W.

[0045] The ratio (B / A) of the flow rate B of the gas supplied to the air diffuser 130 to the flow rate A of the gas supplied to the hollow fiber membrane module 10 is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more. When B / A is equal to or greater than the lower limit, the wastewater W is sufficiently circulated and easily stirred, making it easier to prevent short-passing of the wastewater W. B / A is preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less. When B / A is equal to or less than the upper limit, the efficiency of oxygen supply to the microbial layer on the hollow fiber membrane surface is increased, thereby improving the efficiency of aerobic treatment and anaerobic treatment. The lower and upper limits of B / A can be arbitrarily combined, and for example, a range of 1 to 20 is preferable.

[0046] The flow rate A of the gas supplied to the hollow fiber membrane module 10 is preferably 20 L / min or more, more preferably 25 L / min or more, and even more preferably 30 L / min or more. If the flow rate A is equal to or greater than the lower limit, the efficiency of oxygen supply to the microbial layer on the surface of the hollow fiber membrane is increased, thereby improving the efficiency of aerobic treatment and anaerobic treatment. The flow rate A is preferably 500 L / min or less, more preferably 300 L / min or less, and even more preferably 200 L / min or less. If the flow rate A is equal to or less than the upper limit, excessive oxygen supply to the microbial layer on the surface of the hollow fiber membrane is unlikely, improving the efficiency of anaerobic treatment on the outer side of the microbial layer. The lower and upper limits of the flow rate A can be arbitrarily combined, and, for example, 20 to 500 L / min is preferred.

[0047] The flow rate B of the gas supplied to the air diffuser 130 is preferably 20 L / min or more, more preferably 50 L / min or more, and even more preferably 100 L / min or more. If the flow rate B is equal to or greater than the lower limit, the wastewater W is sufficiently circulated and easily stirred, making it easier to prevent short-passing of the wastewater W. The flow rate B is preferably equal to or less than 1000 L / min, more preferably equal to or less than 800 L / min, and even more preferably equal to or less than 500 L / min. If the flow rate B is equal to or less than the upper limit, the stirring efficiency of the wastewater W is improved. The lower and upper limits of the flow rate B can be arbitrarily combined, and for example, 20 to 1000 L / min are preferable.

[0048] After the biological treatment, the microbial layer is peeled off from the hollow fiber membranes 1, for example, by a bubbling process using an air diffuser (not shown) or the like disposed below the hollow fiber membrane module 10. Then, by using a solid-liquid separation method using a separation membrane or the like (not shown), sludge containing the peeled off microbial layer is recovered, completing the wastewater treatment.

[0049] As explained above, the present invention uses an aeration device arranged so that at least a portion of it does not overlap with the hollow fiber membrane module when viewed from above, and circulates and agitates the wastewater while treating it, thereby suppressing short-pass wastewater. This reduces the likelihood of insufficiently treated wastewater being discharged from the treatment tank, increasing wastewater treatment capacity. Furthermore, using aeration using gas from a blower to agitate the wastewater during treatment can also reduce energy costs. Furthermore, in the present invention, a microbial layer is formed on the surface of the hollow fiber membrane, and oxygen is supplied to the microbial layer by passing it from the inner side to the outer side of the hollow fiber membrane, thereby enabling both aerobic and anaerobic treatment in the microbial layer to be carried out in a single process. This results in higher oxygen utilization efficiency than oxygen supply by aeration, and also allows the device to be made more compact.

[0050] The present invention is not limited to the above-described embodiment. For example, the present invention may be a wastewater treatment device 100A and a wastewater treatment method using the wastewater treatment device 100A illustrated in Fig. 2. The same parts in Fig. 2 as those in Fig. 1 are designated by the same reference numerals, and description thereof will be omitted. The wastewater treatment device 100A is similar to the wastewater treatment device 100 except that it includes two hollow fiber membrane modules 10A and 10B.

[0051] In the wastewater treatment device 100A, an air diffuser 130 is disposed between two hollow fiber membrane modules 10A and 10B. When the wastewater treatment device is equipped with multiple hollow fiber membrane modules, it is preferable to dispose an air diffuser between any two hollow fiber membrane modules. This makes it easier to thoroughly agitate the wastewater in the treatment tank through the air diffused by the air diffuser, thereby improving the wastewater treatment capacity. When the wastewater treatment device is equipped with a plurality of hollow fiber membrane modules, it is preferable that an air diffuser is disposed between each pair of adjacent hollow fiber membrane modules.

[0052] In the wastewater treatment device 100A, the total flow rate of the gases supplied to the hollow fiber membrane module 10A and the hollow fiber membrane module 10B is defined as flow rate A, and the ratio (B / A) is preferably controlled within the above range.

[0053] The present invention may also be applied to a wastewater treatment device 100B and a wastewater treatment method using the wastewater treatment device 100B illustrated in Fig. 3. The same parts in Fig. 3 as those in Fig. 1 are designated by the same reference numerals, and description thereof will be omitted. The wastewater treatment device 100B is similar to the wastewater treatment device 100 except that it is provided with two air diffusers 130A and 130B.

[0054] In the wastewater treatment device 100B, an air diffuser 130A and an air diffuser 130B are disposed on both sides of the hollow fiber membrane module 10. This further increases the efficiency of agitating the wastewater by the air diffusers, thereby improving the wastewater treatment capacity. The flow rate B1 of the gas supplied to the air diffuser 130A and the flow rate B2 of the gas supplied to the air diffuser 130B may be the same or different.

[0055] In the wastewater treatment device 100B, when the flow rates B1 and B2 are the same, the ascending flows join together near the horizontal center of the hollow fiber membrane module 10, generating a downward flow, as shown in Fig. 3. On the other hand, when the flow rate B2 is greater than the flow rate B1, the ascending flows join together near the horizontal air diffuser 130A in the hollow fiber membrane module 10, generating a downward flow, as shown in Fig. 4. The opposite occurs when the flow rate B1 is greater than the flow rate B2. In this way, when treatment is performed under conditions where the flow rates B1 and B2 are different, the flow path of the wastewater W is disturbed, further increasing the stirring efficiency of the wastewater W. For this reason, when a wastewater treatment apparatus equipped with a plurality of aeration devices is used, the wastewater treatment method of the present invention preferably includes treating the wastewater by supplying gas at different flow rates to any two aeration devices.

[0056] In the wastewater treatment device 100B, the sum of the flow rates B1 and B2 is defined as the flow rate B, and the ratio (B / A) is preferably controlled within the above-mentioned range.

[0057] 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. [Explanation of symbols]

[0058] 1...hollow fiber membrane, 10, 10A, 10B...hollow fiber membrane module, 11...hollow fiber membrane sheet, 12...housing, 12A...upper housing, 12B...lower housing, 100...wastewater treatment device, 110...treatment tank, 120...gas supply line, 130, 130A, 130B...aeration device, W...wastewater.

Claims

1. A wastewater treatment method using a wastewater treatment device that utilizes a microbial layer derived from microorganisms in wastewater formed on the surface of a hollow fiber membrane, comprising: The wastewater treatment device includes a treatment tank in which wastewater is treated, a hollow fiber membrane module including hollow fiber membranes, and a plurality of air diffusers; the hollow fiber membrane module and the plurality of aeration devices are immersed in the wastewater in the treatment tank; the plurality of air diffusers are arranged at positions where at least a portion of them does not overlap the hollow fiber membrane module when viewed from above, A wastewater treatment method comprising: treating wastewater by constantly operating at least one of the aeration devices; and treating wastewater by supplying gases at different flow rates to any two of the aeration devices.

2. A wastewater treatment method as described in claim 1, wherein at least one of the aeration devices is positioned at a lower position than the hollow fiber membrane module.

3. A wastewater treatment method as described in claim 1 or 2, wherein the wastewater treatment device is provided with a plurality of the hollow fiber membrane modules, and at least one aeration device is arranged between any two of the hollow fiber membrane modules when viewed from above.

4. A wastewater treatment method described in any one of claims 1 to 3, wherein the flow rate B of gas supplied to at least one of the aeration devices is greater than the flow rate A of gas supplied to the hollow fiber membrane module.

5. The wastewater treatment method according to any one of claims 1 to 4, wherein a ratio (B / A) of a flow rate B of the gas supplied to at least one of the air diffusers to a flow rate A of the gas supplied to the hollow fiber membrane module is 1 to 20.

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