JP2015182015A - Apparatus and method for treating water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for treating water with which water can be treated while saving more energy.SOLUTION: The apparatus for treating water includes: a storage tank 1 for storing water X to be treated; a membrane module 2 for treating the water X to be treated; a return pipe 4 which is connected to the storage tank 1 and the membrane module 2 and used for returning the water treated in the membrane module 2 to the storage tank 1; and a first gas supply unit 5 which is connected to the return pipe 4 and used for supplying gas to the return pipe 4. The end of the return pipe 4 on the storage tank side is set at a position higher than the position of connection of the return pipe 4 with the first gas supply unit 5 in a vertically upward direction.

Description

  The present invention relates to a water treatment apparatus and a water treatment method, and more particularly to a water treatment apparatus and a water treatment method capable of treating water to be treated with energy saving.

  Conventionally, water to be treated has been purified by a water treatment apparatus provided with a polymer water treatment membrane. Examples of the purification of water to be treated include turbidity of river water and groundwater, clarification of industrial water, treatment of drainage and sewage, pretreatment for desalination of seawater, and the like. The polymer water treatment membrane is often a hollow fiber-like porous membrane (hereinafter also referred to as “hollow fiber membrane”) made of a polymer material. This is because the hollow fiber membrane easily separates various components contained in the water to be treated.

  The form of the water treatment apparatus is classified into two types, “immersion type” and “outside tank type”, depending on the installation position of the membrane module. In the former, the membrane module is installed in the tank of the water to be treated, and in the latter, the membrane module is installed outside the tank of the water to be treated. For example, Patent Literature 1 (Japanese Patent Application Laid-Open No. 2004-358410) discloses a water treatment apparatus outside the tank. This water treatment apparatus uses “cross-flow filtration / backwash” in which the water to be treated is filtered or backwashed while being circulated through the membrane module.

JP 2004-358410 A

  In general, a supply pump is used to circulate the water to be treated. However, the supply pump requires a great deal of energy to transfer the water to be treated. Therefore, recently, an “air lift” that can transfer the water to be treated with more energy saving has been adopted. The air lift is provided with an air introduction part immediately before the membrane module. Air is supplied from the front side of the membrane module through the air introduction part, and the water to be treated is circulated by the force of the air.

  In recent years, the need for improvement in energy efficiency has increased, and therefore, the advent of a water treatment apparatus that can treat water to be treated with energy saving rather than the air lift is desired.

  This invention is made | formed in view of the said present condition, The objective is to provide the water treatment apparatus and the water treatment method which can process to-be-processed water by energy saving.

In order to solve the above-mentioned problems, the present inventors have studied the gas supply position in the water treatment apparatus, thereby completing the present invention described below. That is,
[1] A water treatment apparatus of the present invention stores a treated water treated by a membrane module, connected to the storage tank for storing the treated water, a membrane module for treating the treated water, and the storage tank and the membrane module. A return pipe that is supplied to the tank and a first gas supply device that is connected to the return pipe and supplies gas to the return pipe, and the end of the return pipe on the storage tank side includes the return pipe and the first gas supply device It is characterized by being in a position higher in the vertical direction than the connection position.
[2] The diameter of the return pipe from the membrane module to the first gas supply device is preferably equal to or less than the diameter of the return pipe from the first gas supply device to the storage tank.
[3] The membrane module is arranged outside the storage tank, and the storage tank and the membrane module may be connected via a supply pipe.
[4] The membrane module may be disposed in the storage tank.
[5] The first gas supply device preferably includes a gas supply pipe that supplies gas to the return pipe.
[6] The present invention is a water treatment method using the water treatment device according to any one of [1] to [5], wherein the level of the water to be treated in the storage tank is on the storage tank side of the return pipe. It is also a water treatment method for treating the water to be treated in a state higher than the end.
[7] It is preferable to treat the water to be treated in a state in which the level of the water to be treated in the storage tank is higher than the uppermost portion in the vertical direction of the membrane module.
[8] It is preferable that the difference between the level of the water to be treated in the storage tank and the end of the return pipe on the storage tank side is 250 mm or less.
[9] The in-pipe flow velocity of the water to be treated in the return pipe is preferably 0.3 m / s or more and 2.0 m / s or less.

  The water treatment apparatus and the water treatment method of the present invention exhibit an excellent effect that the water to be treated can be treated with more energy saving.

It is a conceptual diagram which shows the water treatment apparatus of Embodiment 1. It is the elements on larger scale which show an example of the structure which supplies gas to a return pipe from a 1st gas supply apparatus. It is the elements on larger scale which show an example of the structure which supplies gas to a return pipe from a 1st gas supply apparatus. It is the elements on larger scale which show an example of the structure which supplies gas to a return pipe from a 1st gas supply apparatus. It is a schematic sectional drawing of the membrane module used by this invention. It is a conceptual diagram which shows the water treatment apparatus of Embodiment 2. It is a conceptual diagram which shows the water treatment apparatus of Embodiment 3. It is a conceptual diagram which shows the water treatment apparatus of Embodiment 4. It is a conceptual diagram which shows the water treatment apparatus of Embodiment 5. It is a conceptual diagram which shows the water treatment apparatus of Embodiment 6. It is a conceptual diagram which shows the water treatment apparatus of Embodiment 7. It is a conceptual diagram which shows the water treatment apparatus of Embodiment 8. It is a conceptual diagram which shows the water treatment apparatus of Embodiment 9. It is a conceptual diagram which shows the modification of the water treatment apparatus of Embodiment 9.

<Embodiment 1>
(Water treatment equipment)
FIG. 1 is a schematic diagram illustrating an outline of the water treatment apparatus according to the first embodiment. As shown in FIG. 1, the water treatment apparatus of the present embodiment is connected to a storage tank 1 that stores the treated water X, a membrane module 2 that treats the treated water X, and the storage tank 1 and the membrane module 2. The return pipe 4 includes a return pipe 4 that returns the treated water treated by the membrane module 2 to the storage tank 1, and a first gas supply device 5 that is connected to the return pipe 4 and supplies gas to the return pipe 4. The storage tank side end portion is characterized by being in a position higher in the vertical direction than the connection position of the return pipe 4 and the first gas supply device 5. In the water treatment apparatus of the present invention, as shown in FIG. 1, the membrane module 2 is disposed outside the storage tank 1. The storage tank 1 and the membrane module 2 are connected via a supply pipe 3. The supply pipe 3 supplies the water to be treated X in the storage tank 1 to the membrane module 2.

  The water treatment apparatus of the present invention will be described with reference to FIG. First, the treated water X to be treated is stored in the storage tank 1. Then, the treated water X in the storage tank 1 is supplied to the membrane module 2 through the supply pipe 3. The treated water X is treated by passing the treated water X through the membrane module 2. The treated water treated by the membrane module 2 is returned to the storage tank 1 via the return pipe 4. A first gas supply device 5 is connected to the return pipe 4. Air is supplied from the first gas supply device 5 to the return pipe 4. This air serves as a power source and the permeate is returned to the storage tank 1. The water to be treated is treated by the membrane module 2 by these series of flows. Below, each part which comprises the water treatment apparatus of this embodiment is demonstrated, referring FIG.

(First gas supply device)
The first gas supply device 5 is a power source for circulating the water to be treated X in the water treatment device. The water treatment device of this embodiment is characterized in that the first gas supply device 5 is connected to the return pipe 4. By providing the first gas supply device 5 at this position, it is not necessary to provide a conventionally required liquid supply device or air supply device. Moreover, the energy efficiency of the water treatment can be improved by providing the first gas supply device 5 on the return pipe 4 side.

  The conventional air lift has a gas supply device connected to the supply pipe 3. When a gas supply device is connected to this position, the pressure loss in the membrane module 2 is excessive, so it was necessary to supply more gas than is necessary for air scrubbing. In addition, since air easily accumulates in the piping, the water to be treated cannot be circulated efficiently. Moreover, in the conventional water treatment apparatus, air is not evenly distributed in the membrane module, and the flow of water to be treated in the membrane module is biased.

  By connecting the first gas supply device 5 to the return pipe 4 as in the water treatment device of the present embodiment, air can be supplied without pressure loss in the membrane module. Further, air is less likely to accumulate in the supply pipe 3 and the return pipe 4. For this reason, air can be uniformly distributed and supplied in the membrane module. Due to these factors, the energy efficiency of water treatment can be increased.

  Examples of the gas supplied by the first gas supply device 5 include air, compressed air, ozone, nitrogen, carbon dioxide, and the like, but compressed air is preferable. Moreover, it is preferable that gas is supplied with the form of a bubble, More preferably, it is a microbubble about several dozen micrometer-several hundred micrometer. Microbubbles have the advantage of easily circulating the water to be treated. As a method for supplying air bubbles, for example, a diffuser tube in which air discharge holes of about 1 mm to several tens of mm are formed in stainless steel, ceramic, plastic, rubber or the like may be used. Examples of the first gas supply device 5 include a blower, a compressor, and a microbubble generating blower.

(Return pipe)
The return pipe 4 is connected to the storage tank 1 and the membrane module 2 and is provided to supply the water to be treated treated by the membrane module 2 to the storage tank 1. The supply pressure when supplying the water to be treated to the return pipe 4 is preferably 20 kPa or more and 100 kPa or less. The return pipe 4 may be provided with an air release line for extracting air from the return pipe.

  The inner diameter of the return pipe can be arbitrarily set, but is preferably 10 mm or more and 250 mm or less, more preferably 30 mm or more and 400 mm or less, and further preferably 40 mm or more and 200 mm or less. By using such an inner diameter, pressure loss can be reduced and transfer efficiency can be increased.

  The diameter of the return pipe from the membrane module to the first gas supply device is preferably equal to or less than the diameter of the return pipe from the first gas supply device to the storage tank, and the return from the membrane module 2 to the first gas supply device 5 When the diameter of the pipe 4 is R and the diameter of the return pipe 4 from the first gas supply device 5 to the storage tank 1 is r, r / R is preferably 1.0 ≦ r / R ≦ 2.0. 1.2 ≦ r / R ≦ 1.6 is more preferable. Thus, by increasing the diameter r of the return pipe 4 from the first gas supply device 5 to the storage tank 1, the water supply pressure of the water to be treated by air can be increased, and the water to be treated is efficiently circulated. be able to. “Diameter” here means the diameter of a circle when the return pipe is cut along a cross section perpendicular to the direction of the water to be treated.

  The return pipe 4 preferably has one or more regions (hereinafter also referred to as “vertical stretching regions”) extending substantially vertically upward, and more preferably the first gas supply device 5 is connected to a region below the vertical stretching region. . This is because air buoyancy works vertically upward in water, and this buoyancy maximizes the function of supplying water to be treated. The above “substantially vertically upward” means that it may be inclined ± 10 ° or less from the vertically upward direction.

  As shown in the enlarged view of FIG. 1, the return pipe 4 passes through the membrane module 2 to the bottom of the return pipe 4 due to its own weight, and is supplied to the storage tank 1 by the air supplied from the bottom. It is preferable to set the shape of the return pipe 4 so as to be returned. For this reason, it is more preferable that the return pipe 4 has two or more vertically extending regions. In that case, it is necessary to connect the 1st gas supply apparatus 5 to the downward area | region of the perpendicular | vertical extending | stretching area | region nearest to the storage tank 1. FIG. If there are two or more vertically extending regions between the storage tank 1 and the first gas supply device 5, an air pool is generated in the return pipe 4, which is not preferable.

  The vertically extending region has a function of circulating the water to be treated by air buoyancy and a function of circulating the water to be treated by its own weight. With these functions, water to be treated can be treated efficiently. For example, the water treatment apparatus of FIG. 1 has two vertically extending regions. The right vertical extension region in the enlarged view of FIG. 1 feeds the treated water by its own weight, and the left vertical stretch region in the enlarged view of FIG. 1 draws the treated water by air buoyancy. Deliver liquid.

  The length of the vertical extension region of the return pipe is preferably 0.1 m or more and 10 m or less, more preferably 0.5 m or more and 5 m or less, and further preferably 1 m or more and 4 m or less. In addition, regarding the relationship between the length of the vertical extension region of the return pipe and the water depth of the storage tank 1, the length of the vertical extension area of the return pipe is preferably 50% or more of the effective water depth in the storage tank 1, 70% More preferably, it is 90% or more. Here, the “effective water depth” means the water depth of the storage tank designed to operate the water treatment apparatus on a regular basis. By setting it as such length, it becomes easy to obtain the buoyancy of air for to-be-processed water, and to-be-processed water can be circulated efficiently.

  The return pipe 4 between the connection portion with the first gas supply device 5 and the storage tank 1 preferably includes a portion extending in a substantially horizontal direction, and the portion extending in the substantially horizontal direction is connected to the storage tank 1. It is preferable. In this way, by connecting the first gas supply device 5 to the storage tank 1 with the return pipe, it is difficult to store air in the return pipe.

  The timing which the 1st gas supply apparatus 5 supplies gas is not specifically limited, You may carry out in any process of water treatment, backwashing, or flushing. Although the time for supplying the gas varies depending on the size of the bubble, it is continuously 1 second or longer, 1 minute or longer, preferably several seconds to several minutes, and it is more preferable to constantly supply the gas. The bubbles introduced into the membrane module are preferably supplied in a volume of 0.25 or more and 2.5 or less with respect to the raw water volume (raw water ratio) introduced into the membrane module. Usually, the volume ratio between the amount of gas and the water to be circulated depends on the water level difference, the pipe resistance before and after the module, the flow resistance in the module, the uniformity of the air flow in the module, and the like.

(Gas supply method)
1A to 1C are partially enlarged views showing an example of a configuration for supplying gas from the first gas supply device 5 to the return pipe 4. As shown in FIGS. 1A to 1C, the first gas supply device 5 is preferably connected to a point where the return pipe 4 changes its path from the horizontal direction to the vertical direction. The first gas supply device 5 preferably includes a gas supply pipe 8. The gas supply pipe 8 is a pipe having a diameter smaller than the diameter of the return pipe 4, and one end is connected to the first gas supply device 5 and the other end is arranged inside the return pipe 4.

  The diameter of the gas supply pipe 8 is preferably 5% to 30% with respect to the diameter of the return pipe 4, and more preferably 10% to 20%. By having such a diameter, the water to be treated can be circulated smoothly without hindering the flow of the water to be treated. If the diameter of the gas supply pipe 8 is too large, the flow of the water to be treated will be hindered. This is not desirable, and if the diameter of the gas supply pipe 8 is too small, the proportion of bubbles occupied in the cross section of the gas supply pipe 8 will be small. As a result, the levitating efficiency of the water to be treated decreases.

  With reference to FIG. 1A, the preferable arrangement | positioning of the end of the gas supply pipe | tube 8 and the return pipe | tube 4 is further demonstrated. The other end of the gas supply pipe 8 is disposed so as to be positioned above the upper end of the horizontal path on the upstream side of the return pipe 4 and the extension line parallel to the upper end (dotted line in FIG. 1A) in the vertically upward direction. Is preferred. By arranging in this way, the gas supplied from the first gas supply device 5 to the return pipe 4 has an exceptional effect that it is difficult to flow backward to the upstream side.

  FIG. 1B is the same as the configuration of FIG. 1A except that a recess is provided below the gas supply pipe with respect to the configuration of FIG. 1A. Such a recess can appropriately secure the distance of the vertical extending region even when the upstream horizontal path is difficult to connect to the lower end of the vertical extending region.

  FIG. 1C is the same as the configuration of FIG. 1A except that the gas supply direction is different from the configuration of FIG. 1A. That is, in the configuration of FIG. 1A, gas is supplied from the vertically downward direction, but in the configuration of FIG. 1C, gas is introduced from the horizontal direction. This configuration is, for example, when the space for providing the first gas supply device cannot be secured at a point where the direction of the return pipe changes (that is, a point where the direction of the return pipe changes from the horizontal direction to the vertical direction). It is possible to arrange the supply device.

(Supply pipe)
The supply pipe 3 is connected to the storage tank 1 and the membrane module 2 and is provided to supply the treated water X to the membrane module 2. The supply pressure when supplying the water to be supplied to the supply pipe 3 is preferably 20 kPa or more and 100 kPa or less, for example.

(Reservoir)
The storage tank 1 is a tank for storing treated water. The storage tank 1 is connected to a supply pipe 3 for supplying water to be treated to the membrane module 2 and a return pipe 4 for returning permeated water from the membrane module 2. The storage tank 1 may be a single unit of about 2 m × 10 m or a connected storage tank, or may be a single tank of about 5 m × 50 m or a connected storage tank.

(Treated water)
The treated water includes wastewater containing activated sludge from sewage treatment plants, urban sewage such as household wastewater, industrial wastewater, agricultural wastewater, biologically treated water, seawater, well water, river water, lake water, etc. It may be a liquid food such as milk. Suspended solids (SS) is preferably less than 20000.

(Membrane module)
As shown in FIG. 2, the membrane module 2 includes a plurality of hollow fiber membranes 9 and a cylindrical case 10 that houses the hollow fiber membranes 9. The outer diameter, length, number, etc. of the hollow fiber membrane 9 can be appropriately adjusted according to the characteristics of the membrane module to be obtained. A predetermined number of the hollow fiber membranes 9 may be bundled to form a hollow fiber membrane bundle. The hollow fiber membrane bundle is preferably straight. The hollow fiber membrane bundle is preferably cut into a predetermined length according to the cylindrical case 10 and inserted into the case. When the membrane module 2 is loaded with a pressure difference between the inner and outer membranes, water in the water to be treated permeates through the hollow fiber membrane, and suspended matter in the water to be treated is collected in the hollow fiber membrane. The permeated water that has passed through the hollow fiber membrane is sent to the storage tank 1. In this way, unnecessary substances in the water to be treated are removed.

(Hollow fiber membrane)
In this embodiment, the hollow fiber membrane is formed of a single main constituent material having a self-supporting structure. Here, “single main constituent material” means that the main material is a single material. That is, the material forming the hollow fiber membrane (for example, the resin constituting the membrane) is 50% by mass or more (preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more), More preferably 85% by mass or more, or the properties of the one kind of resin dominate the properties of the constituent materials. Specifically, it means a material in which one kind of resin has 50 to 99% by mass.

  The above “having a self-supporting structure” means that when the hollow fiber membrane is used, the shape thereof has a strength that can maintain a desired shape such as a cylindrical shape. The hollow fiber membrane used in the present embodiment does not require a support of a strong material (ceramic, non-woven fabric, etc.) and preferably has a sufficient strength with a single constituent material.

  Moreover, it is preferable that the hollow fiber membrane used by this embodiment has a separation function more than microfiltration on both front and back surfaces. By forming a hollow fiber membrane with a single main constituent material as in this embodiment, a separation function is provided on both the front and back surfaces, preventing contamination during backwashing and avoiding contamination inside the hollow fiber membrane. It is also possible. Further, even when one surface of the hollow fiber membrane is clogged or damaged, the separation function can be secured by the other surface.

  Regarding the diameter of the hollow fiber membrane 9, normally, when the inner diameter of the hollow fiber membrane 9 is thin, resistance when air passes is large, and the water to be treated tends to be difficult to circulate. In order to increase the amount of circulation, since the hollow fiber membrane preferably has a large diameter, the outer diameter of the hollow fiber membrane 9 is preferably a large diameter of 3.6 mm to 10 mm.

  The strength of the hollow fiber membrane is determined by various factors such as the material, the inner diameter, the wall thickness, the roundness, the inner structure, etc. Among them, it is effective to use the SDR value (outer diameter / wall thickness ratio). It is. In order to achieve the pressure resistance performance of the internal and external pressures of 0.3 MPa, it is preferable to design the SDR value to be about 34 or less. On the other hand, when the SDR value is reduced, the filtration area of the membrane module is lowered, so that the SDR is preferably 5.8 or more.

  The SDR value is preferably about 5.9 or more, about 6.0 or more, about 6.5 or more, or about 7 or more, preferably about 32 or less, about 30 or less, about 25 or less, or about 20 or less. More preferably, it is about 16 or less and about 11 or less. In particular, when the outer diameter is about 5 to 7 mm, the SDR value is preferably about 4 to 16, and more preferably set to about 6.5 to 11.

  In addition, although an internal diameter is determined by the outer diameter and wall thickness, 1.6 mm-9.4 mm are mentioned, and are 4.0 mm or more, 4.5 mm or more, and 5.0 mm or more. Moreover, Preferably it is 20 mm or less, Furthermore, 10 mm or less or 8 mm or less is mentioned. In particular, an inner diameter of 4 mm to 8 mm is suitable. In this case, a wall thickness of 0.1 mm to 2 mm is suitable.

  Although various materials, such as a metal and a plastic, can be used for the cylindrical case 10, a plastic is preferable from a viewpoint that molding is easy and it is easy to ensure mechanical strength. Examples of the plastic include those containing acrylic resin, polystyrene resin, ABS resin, AS resin, polycarbonate resin, vinyl chloride resin, and the like.

  Both end surfaces 10 a and 10 b of the plurality of hollow fiber membranes 9 are sealed in a cylindrical case 10 via a sealing material 11. The sealing material 11 is formed by, for example, potting by centrifugal molding. The material of the sealing material 11 is preferably a material having a low initial viscosity, a viscosity that increases with time and cures, and finally cures to a predetermined hardness. Examples of such materials include epoxy resins and urethane resins. Can be mentioned.

  The membrane module 2 is disposed on the downstream side (permeate tank side) of the storage tank 1 and the gas supply device 5. The membrane module 2 may be used alone or in combination of two or more. When two or more membrane modules are used, each membrane module may be connected in series, may be connected in parallel, or a combination of series and parallel may be used. From the viewpoint of increasing energy efficiency, the membrane modules are preferably connected in series. When using the water treatment apparatus of this embodiment for the concentration of to-be-processed water, it is preferable to connect the membrane module 2 combining serial and parallel.

  A primary side (permeate extraction side) pipe port 12 is disposed on the cylindrical case side surfaces 10 a and 10 b between the sealing materials 11. A permeate side conduit (not shown) for connecting the inside of the case and the outer space of the hollow fiber membrane 9 is connected to the primary side port 12. Two or more primary side pipe ports 12 may be arranged. Moreover, the secondary side (to-be-processed water supply side) pipe port 13 is arrange | positioned in case side surface 10a, 10b of an end surface (one end surface or both end surfaces) rather than the sealing material 11. FIG. A treated water supply conduit (not shown) for communicating with the inner (hollow) space of the plurality of hollow fiber membranes 9 described above is connected to the secondary side pipe port 13. As the membrane module, for example, those described in JP-A-62-2140607, JP-A-6-319961, JP-A-2009-183822, etc. may be used.

  When a certain period of time elapses from the start of water treatment, suspended matter or the like accumulates on the membrane module 2, and the separation performance of the membrane module 2 may be reduced. At this time, backwashing may be performed. Backwashing is performed by using the first gas supply device 5 as a power source and returning a part of the water to be treated in the storage tank 1 to the membrane module 2 as backwashing water. As a result, suspended matter or the like attached to the membrane module 2 can be peeled off, and the processing performance of the membrane module can be regenerated.

  In the constant pressure filtration, the backwashing is preferably performed when the decrease in water permeability is 20% or more, and in the quantitative filtration, it is preferably performed when the increase in transmembrane pressure difference is 20% or more. The backwashing is preferably performed with a variation in transmembrane pressure difference within 10%. Thereby, the frequency | count of backwashing by a high voltage | pressure can be reduced, and a hollow fiber membrane can be lengthened.

(Water treatment method)
The water treatment method using the water treatment apparatus of the present embodiment is preferably a cross flow method. In the cross flow method, the membrane surface of the hollow fiber membrane and the flow direction of the water to be treated are substantially parallel, and the suspended matter attached to the membrane surface of the hollow fiber membrane can be peeled and circulated. Thereby, clogging of the hollow fiber membrane is suppressed, and the treatment speed of the water to be treated is stabilized.

  From the viewpoint of efficiently circulating the water to be treated, the water to be treated is treated in a state where the liquid level of the water to be treated X in the storage tank 1 is higher than the connection position between the return pipe 4 and the storage tank 1. Is preferred. By setting it as such a positional relationship, to-be-processed water can be circulated with the water pressure of to-be-processed water. In addition, you may process a to-be-processed water in the state where the liquid level of the to-be-processed water X in the storage tank 1 is lower than the connection position of the return pipe 4 and the storage tank 1. FIG.

  From the viewpoint of efficiently circulating the water to be treated, the difference between the level of the water to be treated X in the storage tank 1 and the end of the return pipe 4 on the storage tank side is preferably 250 mm or less, and 200 mm More preferably, it is 150 mm or less. Furthermore, the efficiency is best when the end of the return pipe 4 on the storage tank side is below the water surface and the difference is 250 mm or less. Moreover, it is preferable that the in-pipe flow velocity of to-be-processed water is 0.3 m / s or more and 2 m / s or less, More preferably, it is 0.5 m / s or more and 1.5 m / s or less, More preferably, it is 0.8. It is 7 m / s or more and 1 m / s or less. In addition, the value computed based on the volume of the to-be-processed water circulated per unit time shall be employ | adopted for the pipe | tube flow velocity.

  Moreover, it is preferable to process to-be-processed water in the state in which the liquid level of the to-be-processed water in a storage tank is higher than the uppermost part of the membrane module vertically upward. By setting it as such a positional relationship, to-be-processed water can be permeate | transmitted to the uppermost part of a membrane module with the water pressure of to-be-processed water.

  In order to make it easy to return the permeated water from the membrane module to the storage tank 1, it is preferable that the connection portion between the return pipe 4 and the first gas supply device 5 is lower than the liquid level of the water to be treated in the storage tank. Moreover, in order to make it easy to return permeated water to the storage tank 1 by air, the connecting portion between the return pipe 4 and the first gas supply device 5 is the lowermost portion of the membrane module 2 that faces downward in the vertical direction as shown in FIG. It is preferable that it is in a higher position.

  Here, the transmembrane pressure applied to the membrane module 2 is preferably a permeation pressure of 0 to 300 kPa, more preferably 200 kPa or less. By using such a transmembrane pressure difference, the water permeation performance required in practice is maintained, and the water permeation rate is stable for a long period of time.

  The water to be treated may be treated with an internal pressure type or with an external pressure type. The internal pressure type is a system in which treated water is supplied to the inside of the hollow fiber membrane and the permeated water is taken out from the outside of the hollow fiber membrane. The external pressure type is a system in which water to be treated is supplied to the outside of the hollow fiber membrane and permeate is taken out from the inside of the hollow fiber membrane. From the viewpoint that the film surface flow rate can be set higher, it is preferable to perform the treatment with an internal pressure method.

  When switching between water treatment and backwashing, flushing or draining may be performed, or water treatment may be temporarily stopped.

  Flushing is a process of removing suspended matters attached to the storage tank, each pipe, and the membrane module. Although suspended matter or the like larger than the inner diameter of the hollow fiber membrane may block the circulation path of the water to be treated, this blockage can be prevented by flushing in the direction opposite to the supply direction of the water to be treated. Flushing is preferably performed at a membrane surface flow rate of 0.1 m / s or higher without pressurizing the water to be treated. The water that has passed through the membrane module 2 by flushing is returned to the storage tank 1 as flushing water.

  Draining is a step of discharging suspended matter remaining in the hollow fiber membrane of the membrane module out of the system. Drain is collected by opening the membrane module with the water treatment device stopped and dropping the concentrate, or backwashing with the membrane module opened, and collecting backwash wastewater. To do. The collected concentrated water or backwash waste water may be stored in a drain water tank provided separately.

  Although the water treatment apparatus of this embodiment is not shown in FIG. 1, a biological treatment tank, a flocculant treatment tank, a flocculant injection means, a chemical liquid tank, a chemical liquid injection means, a concentrated water tank, an on-off valve, an ultrasonic generator, etc. May be provided.

(Ultrasonic generator)
An ultrasonic generator (not shown) may be provided in order to peel off suspended matter or the like attached to the hollow fiber membrane of the membrane module 2. The ultrasonic generator is preferably arranged so that only the membrane module 2 is irradiated with ultrasonic waves. The ultrasonic wave may have a frequency of about a few dozen kHz to several GHz. Ultrasonic irradiation may be performed during or during water treatment, backwashing, flushing, or the like. Ultrasonic waves may be irradiated continuously or intermittently.

  When using the water treatment apparatus of this embodiment as a seawater desalination apparatus, it is preferable to perform turbidity treatment such as sand filtration. By executing the turbidity removal treatment, coarse impurities can be removed. Moreover, since dissolved oxygen in to-be-processed water can be raised by supplying air from a 1st gas supply apparatus, the aeration power at the time of using a water treatment apparatus as a biological treatment tank can also be suppressed.

<Embodiment 2>
FIG. 3 is a schematic diagram illustrating an outline of the water treatment apparatus according to the second embodiment. As shown in FIG. 3, the present embodiment is the same water treatment apparatus as that of the first embodiment except that the second gas supply device 6 is connected to the supply pipe 3 with respect to the first embodiment. As shown in the present embodiment, the membrane module can be air scrubbed by providing the second gas supply device 6 in the supply pipe 3. The second gas supply device 6 can be the same as the first gas supply device 5.

<Embodiment 3>
FIG. 4 is a schematic diagram illustrating an outline of the water treatment apparatus according to the third embodiment. As shown in FIG. 4, the present embodiment is carried out except that when the permeate is returned from the return pipe 4 to the storage tank 1, the permeate is returned from a position higher than the liquid level of the water to be treated. It is the same water treatment apparatus as in the first embodiment. By setting the connection position between the return pipe 4 and the storage tank 1 as in this embodiment, the vertical extension region of the return pipe 4 can be lengthened. For this reason, the water to be treated can be easily circulated by air buoyancy.

<Embodiment 4>
FIG. 5 is a schematic diagram illustrating an outline of the water treatment apparatus according to the fourth embodiment. As shown in FIG. 5, the present embodiment is the same water treatment apparatus as that of the first embodiment except that the connection positions of the supply pipe and the return pipe to the membrane module are different.

  Since the conventional water treatment apparatus provided the gas supply device on the supply pipe side, the gas supply device could not be used as a power source of the water to be treated when backwashing. In this embodiment, since the 1st gas supply apparatus 5 is provided in the return pipe 4 side, to-be-processed water can be circulated using a gas supply apparatus as a motive power source also at the time of backwashing.

<Embodiment 5>
FIG. 6 is a schematic diagram illustrating an outline of the water treatment apparatus according to the fifth embodiment. As shown in FIG. 6, this embodiment is the same water treatment apparatus as that of Embodiment 1 except that the return pipe has only one vertical extension region. As in the present embodiment, the water to be treated can be efficiently treated even if there is only one vertical extension region.

<Embodiment 6>
FIG. 7 is a schematic diagram illustrating an outline of the water treatment apparatus according to the sixth embodiment. As shown in FIG. 7, the present embodiment is the same water treatment as that of the first embodiment except that the upper part in the vertical direction of the membrane module 2 is higher than the level of the water to be treated in the storage tank. Device. Thus, even if it arrange | positions a membrane module in a position higher than a storage tank, since the water treatment similar to Embodiment 1 is possible, there exists an advantage that the positional relationship of each structural member can be arrange | positioned freely.

<Embodiment 7>
FIG. 8 is a schematic diagram illustrating an outline of the water treatment apparatus of the seventh embodiment. As shown in FIG. 8, the present embodiment is the same water treatment apparatus as that of the first embodiment except that the membrane module is arranged in a lateral direction with respect to the first embodiment. In the present embodiment, since the first gas supply device is provided on the downstream side of the membrane module, the water to be treated can be circulated even if the orientation of the arrangement of the membrane module is horizontal.

<Embodiment 8>
FIG. 9 is a schematic diagram illustrating an outline of the water treatment apparatus according to the eighth embodiment. As shown in FIG. 9, the present embodiment is the same water treatment apparatus as in the fifth embodiment except that the treated water supply apparatus 7 is connected to the supply pipe 3 with respect to the fifth embodiment.

  By providing the treated water supply device 7 in the supply pipe 3 as in this embodiment, the power source for circulating the treated water can be appropriately switched from the first gas supply device 5 to the treated water supply device 7. .

(Treatment water supply device)
Since the water treatment apparatus of this embodiment circulates to-be-treated water using the 1st gas supply apparatus 5, the to-be-treated water supply apparatus 7 is not necessarily essential, but by providing the to-be-treated water supply apparatus, It becomes easy to adjust the transmembrane pressure and the membrane surface flow velocity with respect to the membrane module 2. Moreover, by providing both the 1st gas supply apparatus 5 and the to-be-processed water supply apparatus 7, it can switch with the timing and conditions of supply of to-be-processed water, and can perform a desired water treatment. Although the to-be-processed water supply apparatus may be provided in the supply pipe 3 as shown in FIG.

  The treated water supply device is not particularly limited as long as the treated water can be circulated. For example, a centrifugal pump, a diffuser pump, a spiral mixed flow pump, a mixed flow pump, a piston pump, a plunger pump, a diaphragm pump, a gear A pump, screw pump, vane pump, cascade pump, jet pump, or the like can be used.

<Ninth Embodiment>
FIG. 10 is a schematic diagram illustrating an outline of the water treatment apparatus of the ninth embodiment. As shown in FIG. 10, the present embodiment is different from the other embodiments in that the membrane module is disposed inside the storage tank 1. By providing the membrane module in the storage tank 1, a supply pipe for connecting the storage tank 1 and the membrane module 2 becomes unnecessary. For this reason, the structure of a water treatment apparatus becomes simple.

  As shown in FIG. 10, the end of the return pipe 4 on the storage tank side may be disposed inside the storage tank 1 without connecting the return pipe 4 and the storage tank 1. Thus, what is necessary is just a structure which the to-be-processed water from the return pipe 4 returns to a storage tank, and it is not necessarily restricted only to the form which connects a return pipe and a storage tank. Moreover, by using an air lift in an open state as in this embodiment, the water to be treated can be circulated efficiently.

  In FIG. 10, the end of the return pipe 4 on the storage tank side is disposed so as to be in contact with the liquid surface of the water to be treated, but as shown in FIG. 11, the end of the return pipe 4 on the storage tank side However, it is preferable to be located vertically downward from the liquid level of the water to be treated. Thus, by arrange | positioning the edge part of the return pipe | tube 4, the gas taken in from the gas supply apparatus can be supplied to the to-be-processed water in a storage tank. When this gas is oxygen, this gas becomes oxygen necessary for the biological treatment generated in the storage tank, so that the biological treatment can proceed simultaneously with the water treatment.

  The present invention is widely used as a water treatment apparatus used for water purification such as clarification of river water and groundwater, clarification of industrial water, drainage and sewage treatment, pretreatment for seawater desalination, etc. It is possible to carry out economical and efficient water treatment.

DESCRIPTION OF SYMBOLS 1 Storage tank 2 Membrane module 3 Supply pipe 4 Return pipe 5 1st gas supply apparatus 6 2nd gas supply apparatus 7 To-be-processed water supply apparatus 8 Gas supply pipe 9 Hollow fiber membrane 10 Case 10a Case side surface 10b Both end surface 11 Seal material 12 Primary side port 13 Secondary side port 14 Bubble X Water to be treated

Claims (9)

A storage tank for storing the water to be treated;
A membrane module for treating the treated water;
A return pipe connected to the storage tank and the membrane module and supplying the treated water treated by the membrane module to the storage tank;
A first gas supply device connected to the return pipe and supplying gas to the return pipe,
An end of the return pipe on the storage tank side is at a position higher in the vertical direction than a connection position between the return pipe and the first gas supply device.   The water treatment device according to claim 1, wherein a diameter of the return pipe from the membrane module to the first gas supply device is equal to or less than a diameter of the return pipe from the first gas supply device to the storage tank.   The water treatment apparatus according to claim 1 or 2, wherein the membrane module is disposed outside the storage tank, and the storage tank and the membrane module are connected via a supply pipe.   The water treatment apparatus according to claim 1, wherein the membrane module is disposed in the storage tank.   The said 1st gas supply apparatus is a water treatment apparatus as described in any one of Claims 1-4 provided with the gas supply pipe which supplies gas to the said return pipe. A water treatment method using the water treatment device according to any one of claims 1 to 5,
A water treatment method for treating water to be treated in a state in which a level of water to be treated in the storage tank is higher than an end of the return pipe on the storage tank side.   The water treatment method according to claim 6, wherein the water to be treated is treated in a state where a liquid surface of the water to be treated in the storage tank is higher than an uppermost portion in a vertical direction of the membrane module.   The water treatment method according to claim 6 or 7, wherein a difference between a level of water to be treated in the storage tank and an end of the return pipe on the storage tank side is 250 mm or less.   The water treatment method according to any one of claims 6 to 8, wherein an in-pipe flow velocity of the water to be treated in the return pipe is 0.3 m / s or more and 2.0 m / s or less.