Method for separating and recovering microorganisms and apparatus for separating and recovering microorganisms

Abstract

To provide a separation recovery method of a microorganism and a separation recovery device of a microorganism which enable suppression of clogging of hollow fiber membranes and furthermore enable microorganisms to be stably separated and recovered at higher concentration.SOLUTION: A separation recovery method of a microorganism according to the present invention comprises: a first step of separating and concentrating a microorganism in liquid S1 by using a hollow fiber membrane; a second step of peeling the microorganism by performing reverse passage of the hollow fiber membrane; a third step of supplying compressed air to the hollow fiber membrane and extruding and recovering microorganism concentration water; a fourth step of cleaning the hollow fiber membrane by reversely cleaning the hollow fiber membrane by a liquid amount smaller than that of the reverse passage in the second step after extruding the microorganism concentration water in the third step; and a fifth step of supplying the compressed air to the hollow fiber membrane thereby discharging the cleaning water. A separation recovery device 1 of a microorganism according to the present invention comprises: first means which performs the first step; second means which performs the second step; third means which performs the third step; fourth means which performs the fourth step; and fifth means which performs the fifth step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for separating and recovering microorganisms and an apparatus for separating and recovering microorganisms. [Background technology]

[0002] In recent years, microorganisms, particularly microalgae, have attracted attention as potential sources of biomass fuel, food, cosmetics, etc., and their cultivation in large-scale plants has become widespread. When using microorganisms industrially, it is usually necessary to separate, concentrate, and recover the microorganisms from the culture medium. In recent years, methods for recovering microorganisms have been put into practical use, such as filtering a culture medium using a separation medium such as a mesh filter or a membrane filter, to recover microorganisms at a high recovery rate (see, for example, Patent Document 1).

[0003] However, the method of treating the culture solution using a separation medium has problems such as clogging of the separation medium with microorganisms, their secretions, culture solution components, etc., resulting in high chemical cleaning costs and reduced device operating efficiency. To address this problem, a method has been proposed in which a spring filter with a precoat material pre-coated on the filtering surface is used, and the culture solution is filtered through this spring filter to concentrate the microorganisms, and the difference in specific gravity between the microorganisms and the precoat material is used to separate the precoat material from the concentrated solution and recover the microorganisms (see, for example, Patent Document 2). With this method, the precoat layer is successively renewed, so clogging is reset each time, allowing for stable long-term operation.

[0004] Furthermore, in an internal pressure filtration device in which raw water is passed through the inside of a tubular filtration membrane and permeate is discharged toward the outer surface of the membrane, a method has been proposed in which the filtration operation is interrupted and backwash water is passed from the outer surface of the membrane toward the inner surface, thereby detaching microorganisms that have accumulated on the inside and pushing the detached microorganisms out from the end of the tube (see, for example, Patent Document 3). This method makes it possible to wash away not only the microorganisms that have accumulated on the membrane but also substances that clog the membrane. Furthermore, as a method for reducing the amount of backwash water required in the above-mentioned internal pressure filtration device, a coagulation filtration method has been proposed in which a coagulant is added to raw water to generate flocs, and then solid-liquid separation is performed in a filtration device (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-150768 [Patent Document 2] Japanese Patent Application Publication No. 2018-42470 [Patent Document 3] Japanese Patent Application Publication No. 6-190251 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-170174 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method using a precoated spring filter requires a step of separating the precoat material after concentrating the microorganisms, which takes a long time, and there is also the problem that if the separation is incomplete, the precoat material may become mixed with the microorganisms. In the method of using backwash water to remove microorganisms that have accumulated on the inside, concentrated liquid remains inside the membrane at the end of the filtration process, so if a large amount of backwash water is used to improve cleaning efficiency, the concentrated liquid will be diluted. Conversely, if the amount of backwash water is reduced to prevent dilution, the problem arises that the inner surface of the membrane cannot be sufficiently cleaned. In the method of adding a flocculant and then filtering, the flocculant remains in the concentrated solution of microorganisms. Therefore, when using microorganisms as feed, fertilizer, or pharmaceutical raw materials, for example, it becomes necessary to separate the remaining flocculant, which leads to the problem of complicated processes. An object of the present invention is to provide a method for separating and recovering microorganisms and an apparatus for separating and recovering microorganisms, which can stably separate and recover microorganisms at a higher concentration while suppressing clogging of hollow fiber membranes. [Means for solving the problem]

[0007] The inventors have conducted extensive research into methods for separating and recovering microorganisms from a liquid containing microorganisms by filtration using a hollow fiber membrane. As a result, they have discovered that by performing reverse liquid flow before backwashing the hollow fiber membrane to peel off and recover microorganisms attached to the membrane surface, clogging of the hollow fiber membrane can be suppressed while allowing microorganisms to be separated, concentrated, and recovered stably at a higher concentration, which led to the completion of the present invention.

[0008] That is, the present invention has the following aspects. [1] A step of filtering a liquid S1 containing microorganisms using a hollow fiber membrane to separate and concentrate the microorganisms in the liquid S1; a step of passing the liquid through the hollow fiber membrane in a reverse direction to separate and concentrate the microorganisms from the liquid S1 and adhere to the hollow fiber membrane, while washing the surface of the hollow fiber membrane; supplying compressed air to the hollow fiber membrane and recovering the microorganisms detached from the hollow fiber membrane as microorganism-enriched water, a first step of separating and concentrating the microorganisms in the liquid S1 using the hollow fiber membrane; a second step of passing the liquid S1 through the hollow fiber membrane in a reverse direction to separate and concentrate the microorganisms from the liquid S1 and adhere to the hollow fiber membrane, and then peeling the microorganisms from the hollow fiber membrane; a third step of supplying compressed air to the hollow fiber membrane to push out and recover the microorganisms detached from the hollow fiber membrane as concentrated microorganism water; A fourth step of backwashing the hollow fiber membrane after the microbially concentrated water is extruded from the hollow fiber membrane in the third step to clean the surface of the hollow fiber membrane; a fifth step of supplying compressed air to the hollow fiber membrane and discharging the cleaning water generated in the fourth step from the hollow fiber membrane; and A method for separating and recovering microorganisms, wherein the amount of liquid S2 used for backflow through the hollow fiber membrane in the second step is less than the amount of liquid S3 used for backwashing the hollow fiber membrane in the fourth step. [2] The method for separating and recovering microorganisms according to [1] above, wherein the filtration is internal pressure filtration. [3] The method for separating and recovering microorganisms according to [1] or [2] above, wherein the filtration is dead-end filtration. [4] The method for separating and recovering microorganisms according to any one of [1] to [3] above, wherein the microorganisms are microalgae. [5] The method for separating and recovering microorganisms according to any one of [1] to [4], wherein the cleaning water is returned to a raw water tank that stores the liquid S1. [6] The method for separating and recovering microorganisms according to any one of [1] to [4] above, wherein the washing water is discarded.

[0009] [7] A first means for filtering a liquid S1 containing microorganisms using a hollow fiber membrane to separate and concentrate the microorganisms in the liquid S1; a second means for passing a liquid through the hollow fiber membrane in a reverse direction to separate and concentrate microorganisms from the liquid S1 and adhere to the hollow fiber membrane, and peeling the microorganisms from the hollow fiber membrane; a third means for supplying compressed air to the hollow fiber membrane to push out the microorganisms detached from the hollow fiber membrane as concentrated microorganism water and recovering the microorganisms; A fourth means for backwashing the hollow fiber membrane after the microorganism-enriched water is extruded from the hollow fiber membrane in the third means to clean the surface of the hollow fiber membrane; a fifth means for supplying compressed air to the hollow fiber membrane and discharging the cleaning water generated by the fourth means from the hollow fiber membrane; Equipped with The apparatus for separating and recovering microorganisms, wherein the amount of liquid S2 used for backflow of the hollow fiber membrane in the second means is less than the amount of liquid S3 used for backwashing the hollow fiber membrane in the fourth means. [8] The microorganism separation and recovery device according to [7], wherein the filtration is an internal pressure filtration. [9] The microorganism separation and recovery device according to [7] or [8], wherein the filtration is dead-end filtration.

[10] The apparatus for separating and recovering microorganisms according to any one of [7] to [9] above, wherein the microorganisms are microalgae.

[11] A raw water tank for storing the liquid S1; The microorganism separation and recovery device according to any one of [7] to

[10] above, further comprising a cleaning water return flow path for returning the cleaning water to the raw water tank.

[12] The microorganism separation and recovery device according to any one of [7] to

[10] above, further comprising a wash water waste flow path for disposing of the wash water. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for separating and recovering microorganisms and an apparatus for separating and recovering microorganisms, which can stably separate and recover microorganisms at a higher concentration while suppressing clogging of hollow fiber membranes. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing an example of a microorganism separation and recovery device according to the present invention. [Figure 2] FIG. 1 is an explanatory diagram schematically illustrating an example of each step in the method for separating and recovering microorganisms of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The method for separating and recovering microorganisms of the present invention is a method for filtering a liquid S1 containing microorganisms to separate and concentrate the microorganisms. The microorganism separation and recovery device of the present invention is a device that filters a liquid S1 containing microorganisms to separate and concentrate the microorganisms. Hereinafter, one embodiment of the method for separating and recovering microorganisms and the apparatus for separating and recovering microorganisms according to the present invention will be described in detail with reference to FIGS. 1 and 2 as appropriate. In addition, in each drawing used in the following description, characteristic portions may be enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of each component may differ from the actual ones. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them and can be implemented with appropriate changes within the scope of the present invention.

[0013] [Microorganism separation and recovery device] FIG. 1 shows an example of the apparatus for separating and recovering microorganisms according to the present invention. The microorganism separation and recovery device 1 shown in Figure 1 includes a raw water tank 10 for storing a liquid S1 containing microorganisms, a membrane module 20 equipped with a hollow fiber membrane for filtering the liquid S1, a permeated water tank 30 for storing the permeated water that has passed through the hollow fiber membrane, a concentrated water tank 40 for storing the microorganism-concentrated water (hereinafter also simply referred to as "concentrated water") obtained in the membrane module 20, a supply means 50 for supplying compressed air to the hollow fiber membrane, and a wastewater tank 60 for storing the cleaning water generated by backwashing the hollow fiber membrane.

[0014] The raw water tank 10 is a tank that stores liquid S1 containing microorganisms. Note that, although this will be described in detail later, depending on the concentration of microorganisms in the cleaning water generated by backwashing the hollow fiber membranes, at least a portion of the cleaning water may be received in the raw water tank 10. In other words, the raw water tank 10 is a tank that stores liquid S1 and also receives cleaning water as needed. Furthermore, the raw water tank 10 may be a tank for culturing microorganisms. When culturing microorganisms in the raw water tank 10 is performed in a closed system, it is preferable to use a closed-system culture tank as the raw water tank 10, and when culturing microorganisms in a closed system, it is preferable to use an open-system culture tank as the raw water tank 10. Here, the term "closed system" means that the environment of the culture tank is isolated from the environment outside the culture tank. It is preferable to culture the microorganisms in a closed system because the culture of the microorganisms is less likely to be affected by the environment outside the culture tank and because the culture tank can be prevented from being contaminated with foreign matter such as garbage.

[0015] An example of a closed culture tank is a photobioreactor tank. Examples of photobioreactor tanks include flat-plate tanks, tube-type tanks, solar light-collecting tanks, and internal irradiation tanks. An example of an open-type culture tank is a raceway tank. Instead of an open-type culture tank, microorganisms may be cultured in a pond or the like.

[0016] Liquid S1 is raw water containing microorganisms and is the target for separation and concentration. Examples of microorganisms contained in the liquid S1 include microalgae, yeast, bacteria, filamentous fungi and their spores. Among these, microalgae are suitable for use as biomass fuels, foods, cosmetics, and other materials, and the method and device for separating and recovering microorganisms of the present invention are suitable for filtering the liquid S1 containing microalgae to separate and concentrate the microalgae in the liquid S1.

[0017] Microalgae are single-celled organisms with synthetic functions, with a body length (longest diameter of the cell) of 100 μm or less. Microalgae to be cultured in the present invention are not particularly limited, and examples thereof include cyanobacteria, prokaryotic green algae, red algae, glaucophytes, cryptophytes, dinoflagellates, goldenrod algae, diatoms, brown algae, xanthophytes, haptophytes, raphidophytes (green flagellates), chlorarachniophytes, euglena, prasinophytes, green algae, charophytes, etc. Among these, Euglena, Pseudochoricystis, a type of green algae, and Spirulina, a type of cyanobacteria, are preferred because they contain many nutrients and can be suitably used in foods, cosmetics, etc.

[0018] The raw water tank 10 is connected to a raw water flow path 11 and a wash water return flow path 26, which will be described later. The raw water flow path 11 is a pipe that extracts a portion of the liquid S1, which is raw water, from the raw water tank 10 and supplies the extracted liquid S1 to the membrane module 20. One end of the raw water flow path 11 is connected to the raw water tank 10, and the other end is connected at a first branch point B1 to a first common flow path 22 and a concentrated water flow path 24, which will be described later, so that the liquid S1 is supplied to the membrane module 20 via the first common flow path 22.

[0019] A raw water valve 11a and a raw water pump 11b are installed in the middle of the raw water flow path 11. The raw water valve 11a is a means for adjusting the amount of the liquid S1 supplied to the membrane module 20. The raw water valve 11a can switch between supplying and stopping the liquid S1 to the membrane module 20. The raw water pump 11b is a means for extracting the liquid S1 stored in the raw water tank 10 from the raw water tank 10 and supplying it to the membrane module 20 under pressure.

[0020] The membrane module 20 includes hollow fiber membranes (not shown). The membrane module 20 is a means for filtering the liquid S1 introduced into the hollow fiber membrane, and separating and concentrating the microorganisms in the liquid S1. The filtration method of the membrane module 20 may be either dead-end filtration or cross-flow filtration, but dead-end filtration is preferred. That is, the filtration of the liquid S1 is preferably dead-end filtration. The dead-end filtration method is a method in which the entire amount of supply water is passed through a filter membrane, causing cake (in this embodiment, microorganisms or the like that are filtration residue) to adhere to the filter membrane. On the other hand, the cross-flow filtration method is a method in which the supply water is passed parallel to the filtration surface, thereby preventing suspended matter and colloids (in this embodiment, microorganisms or the like) in the supply water from accumulating on the filter membrane. The membrane module 20 in this example filters the liquid S1 using a dead-end filtration method.

[0021] The types of hollow fiber membranes include microfiltration membranes and ultrafiltration membranes. The average pore size of the micropores formed in the microfiltration membrane is preferably 0.1 to 1 μm. The average pore size of the micropores formed in the ultrafiltration membrane is preferably 0.001 to 0.1 μm. When the average pore size of the micropores is equal to or greater than the above lower limit, the pressure required for solid-liquid separation can be kept sufficiently low. When the average pore size of the micropores is equal to or less than the above upper limit, microorganisms are less likely to leak into the separated liquid.

[0022] Examples of materials for the hollow fiber membrane include cellulose, polyolefin, polysulfone, polyethersulfone (PES), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc. Among these, PVDF, PTFE, and PES are preferred as materials for the hollow fiber membrane because of their resistance to chemicals and pH changes. The outer diameter of the hollow fiber membrane is preferably 0.01 to 3 mm, more preferably 0.05 to 1 mm. If the outer diameter of the hollow fiber membrane is equal to or greater than the above-mentioned lower limit, the inner diameter of the hollow portion of the hollow fiber membrane can be sufficiently ensured, thereby preventing clogging of the hollow fiber membrane by solid matter contained in the feed water supplied to the hollow fiber membrane. If the outer diameter of the hollow fiber membrane is equal to or less than the above-mentioned upper limit, a reduction in the membrane packing amount when fabricating a membrane module can be prevented. 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 two or more and ten or fewer points.

[0023] The membrane module 20 in this example performs filtration by pressure. The pressurization method is not particularly limited, and may be an internal pressure type or an external pressure type, but the internal pressure type is preferred. That is, the filtration of the liquid S1 is preferably performed by internal pressure filtration. Here, the internal pressure type is a filtration method (in-out type) in which feed water flows inside the hollow fiber membrane and permeated water is obtained on the outside, while the external pressure type is a filtration method (out-in type) in which feed water flows outside the hollow fiber membrane and permeated water is obtained on the inside.

[0024] The membrane module 20 is connected to a permeate flow path 21, a first common flow path 22, and a second common flow path 23. The membrane module 20 is also connected to a raw water flow path 11 and a concentrated water flow path 24 via the first common flow path 22, and to a wash water waste flow path 25 and a wash water return flow path 26 via the second common flow path 23. The permeate flow path 21 is a pipe that discharges the permeate that has permeated the hollow fiber membrane of the membrane module 20, i.e., the separated liquid in which microorganisms have been removed from the liquid S1, from the membrane module 20 and supplies it to the permeate tank 30. One end of the permeate flow path 21 is connected to the membrane module 20, and the other end is connected to the permeate tank 30. A permeate valve 21a is installed midway along the permeate flow path 21. The supply and stop of the permeate to the permeate tank 30 can be controlled by opening and closing the permeate valve 21a.

[0025] The first common flow path 22 in this example is a flow path that supplies the liquid S1 that has been extracted from the raw water tank 10 and passed through the raw water flow path 11 to the membrane module 20, and also a flow path that discharges concentrated water that does not pass through the filtration membrane of the membrane module 20 and is enriched in microorganisms from the membrane module 20 and supplies it to the concentrated water flow path 24. One end of the first common flow path 22 is connected to the membrane module 20, and the other end is connected to the raw water flow path 11 and the concentrated water flow path 24 at a first branch point B1.

[0026] The second common flow path 23 in this example is a flow path that discharges cleaning water generated when the hollow fiber membranes of the membrane module 20 are backwashed from the membrane module 20 and supplies it to the cleaning water waste flow path 25, and also serves as a flow path that supplies the cleaning water to the cleaning water return flow path 26. One end of the second common flow path 23 is connected to the membrane module 20, and the other end is connected to the cleaning water waste flow path 25 and the cleaning water return flow path 26 at a second branch point B2. The cleaning water that is discharged from the membrane module 20 and passes through the second common flow path 23 is discarded via the cleaning water waste flow path 25 or returned to the raw water tank 10 via the cleaning water return flow path 26.

[0027] The concentrated water flow path 24 is a pipe that supplies concentrated water in which microorganisms are concentrated and that does not pass through the filtration membrane of the membrane module 20 to the concentrated water tank 40. One end of the concentrated water flow path 24 is connected to the first common flow path 22 and the raw water flow path 11 at a first branch point B1, and the other end is connected to the concentrated water tank 40. A concentrated water valve 24a is installed midway along the concentrated water flow path 24. The supply and stop of concentrated water to the concentrated water tank 40 can be controlled by opening and closing the concentrated water valve 24a.

[0028] The wash water waste flow path 25 is a pipe for discarding the wash water generated when backwashing the hollow fiber membranes of the membrane module 20. In this example, one end of the wash water waste flow path 25 is connected to the second common flow path 23 and the wash water return flow path 26 at the second branch point B2, and the other end is connected to the drainage tank 60, where the wash water is temporarily stored before being discarded. A first cleaning water valve 25a is installed midway along the cleaning water waste flow path 25. The supply and stop of cleaning water to the drain tank 60 can be controlled by opening and closing the first cleaning water valve 25a.

[0029] The cleaning water return flow path 26 is a pipe that returns cleaning water generated when backwashing the hollow fiber membranes of the membrane module 20 to the raw water tank 10. In this example, one end of the cleaning water return flow path 26 is connected to the second common flow path 23 and the cleaning water waste flow path 25 at the second branch point B2, and the other end is connected to the raw water tank 10. A second cleaning water valve 26a is installed midway along the cleaning water return flow path 26. Return and stop of cleaning water to the raw water tank 10 can be controlled by opening and closing the second cleaning water valve 26a.

[0030] The permeated water tank 30 is a tank that stores the permeated water discharged from the membrane module 20. The permeated water tank 30 is not particularly limited as long as it can store permeated water. The permeated water tank 30 is connected to a permeated water flow path 21 and a reverse flow path 31 . The reverse flow path 31 is a pipe that supplies at least a portion of the permeate to the membrane module 20 as a liquid for reverse flow through the hollow fiber membranes of the membrane module 20. One end of the reverse flow path 31 is connected to the permeate tank 30, and the other end merges with the permeate flow path 21 upstream of the permeate valve 21a of the permeate flow path 21 (on the membrane module 20 side), so that the liquid (permeate) for reverse flow through the hollow fiber membranes can be supplied to the permeate flow path 21.

[0031] A reverse liquid flow valve 31a and a reverse liquid flow pump 31b are installed in the middle of the reverse liquid flow path 31. The reverse liquid flow valve 31a is a means for adjusting the amount of permeate supplied to the membrane module 20. The reverse liquid flow valve 31a can switch between supplying and stopping the permeate to the membrane module 20. The reverse liquid pump 31b is a means for extracting the permeated water stored in the permeated water tank 30 from the permeated water tank 30 and supplying it under pressure to the membrane module 20 as a liquid for reverse liquid flow through the hollow fiber membranes.

[0032] The concentrated water tank 40 is a tank that stores the concentrated water discharged from the membrane module 20. The concentrated water tank 40 is not particularly limited as long as it can store concentrated water.

[0033] The supply means 50 is a means for supplying compressed air to the hollow fiber membranes of the membrane module 20 . The supply means 50 in this example includes a compressor 51 and a compressed air flow path 52 . The compressed air flow path 52 is a pipe for supplying compressed air discharged from the compressor 51 to the membrane module 20. One end of the compressed air flow path 52 is connected to the compressor 51. The compressed air flow path 52 branches into two at a third branch point B3, one of which merges with the second common flow path 23 and the other of which merges with the first common flow path 22. In this specification, one of the branches is also referred to as a first compressed air flow path 521, and the other is also referred to as a second compressed air flow path 522. That is, in the illustrated example, the first compressed air flow path 521 merges with the second common flow path 23, and the second compressed air flow path 522 merges with the first common flow path 22.

[0034] A first compressed air valve 521a is installed in the first compressed air flow path 521. A second compressed air valve 522a is installed in the middle of the second compressed air flow path 522. The first compressed air valve 521a and the second compressed air valve 522a are means for adjusting the amount of compressed air supplied to the hollow fiber membranes of the membrane module 20. The first compressed air valve 521a and the second compressed air valve 522a can switch between supplying and stopping compressed air to the hollow fiber membranes of the membrane module 20.

[0035] The wastewater tank 60 is a tank that stores the cleaning water discharged from the membrane module 20. The drain tank 60 is not particularly limited as long as it can store cleaning water.

[0036] [Microorganism isolation and recovery method] An example of the method for separating and recovering microorganisms of the present invention will be described below. The method for separating and recovering microorganisms described below is an example of a method for separating and recovering microorganisms using an apparatus 1 for separating and recovering microorganisms shown in FIG. The method for separating and recovering microorganisms of this embodiment includes the steps of: (A) filtering a liquid S1 containing microorganisms using a hollow fiber membrane to separate and concentrate the microorganisms in the liquid S; (B) passing the liquid through the hollow fiber membrane in the reverse direction to remove the microorganisms that have been separated and concentrated from the liquid S1 and adhered to the hollow fiber membrane from the hollow fiber membrane, while washing the surface of the hollow fiber membrane; and (C) supplying compressed air to the hollow fiber membrane and recovering the microorganisms that have been removed from the hollow fiber membrane as microbially concentrated water. Specifically, this method includes the first, second, third, fourth, and fifth steps shown below. First step: A step (A1) of separating and concentrating microorganisms in a liquid S1 using a hollow fiber membrane. Second step: A step (B1) of passing the liquid through the hollow fiber membrane in the reverse direction to separate and concentrate the microorganisms from the liquid S1 and adhere to the hollow fiber membrane, thereby peeling them off from the hollow fiber membrane. The third step is a step (C1) in which compressed air is supplied to the hollow fiber membrane, and the microorganisms detached from the hollow fiber membrane are pushed out of the hollow fiber membrane as microorganism-enriched water and collected. Fourth step: A step (B2) of backwashing the hollow fiber membrane after the microorganism-enriched water has been pushed out of the hollow fiber membrane in the third step (C1) to clean the surface of the hollow fiber membrane. Fifth step: A step of supplying compressed air to the hollow fiber membrane and discharging the washing water produced in the fourth step from the hollow fiber membrane. Specifically, it is as follows:

[0037] <First step> The raw water valve 11a provided in the raw water flow path 11 and the permeate valve 21a provided in the permeate flow path 21 are opened, and the raw water pump 11b is driven to extract a portion of the liquid S1 from the raw water tank 10 and supply the liquid S1 under pressure to the membrane module 20 via the raw water flow path 11 and the first common flow path 22. At this time, the valves other than the raw water valve 11a and the permeate valve 21a, namely the concentrated water valve 24a, the first cleaning water valve 25a, the second cleaning water valve 26a, the reverse flow valve 31a, the first compressed air valve 521a, and the second compressed air valve 522a, are closed. The liquid S1 is filtered through the hollow fiber membranes of the membrane module 20. In this embodiment, the filtration is dead-end filtration, but cross-flow filtration may also be used. The filtration may be either internal pressure filtration or external pressure filtration, with internal pressure filtration being preferred.

[0038] The permeated water that has permeated through the hollow fiber membranes of the membrane module 20 is discharged from the membrane module 20, and is supplied to the permeated water tank 30 via the permeated water flow path 21 and stored therein. Microorganisms contained in liquid S1 do not pass through the hollow fiber membrane but accumulate on the surface of the hollow fiber membrane. As shown in Figure 2, when liquid S1 is filtered under internal pressure, microorganisms accumulate on the inner surface of the hollow fiber membrane, and when liquid S1 is filtered under external pressure, microorganisms accumulate on the outer surface of the hollow fiber membrane. By filtering the liquid S1 through the hollow fiber membrane in this manner, the microorganisms in the liquid S1 can be separated from the liquid S1 and concentrated.

[0039] <Second process> Next, the raw water pump 11b is stopped, the raw water valve 11a and the permeate valve 21a are closed, the reverse liquid passage valve 31a provided in the reverse liquid passage flow path 31 is opened, the reverse liquid passage pump 31b is driven, a portion of the permeate is extracted from the permeate tank 30, and the liquid is supplied under pressure to the membrane module 20 via the reverse liquid passage flow path 31 and the permeate passage 21 as liquid S2 for reverse liquid passage through the hollow fiber membranes, thereby causing the liquid to pass back through the hollow fiber membranes. At this time, if the filtration of liquid S1 in the first step is performed by the internal pressure method, the reverse liquid passage through the hollow fiber membranes is preferably performed by the external pressure method, and if the filtration of liquid S1 is performed by the external pressure method, the reverse liquid passage through the hollow fiber membranes is preferably performed by the internal pressure method. By passing the liquid through the hollow fiber membrane in this way, the microorganisms that have adhered to the hollow fiber membrane can be separated and concentrated from the liquid S1 and peeled off from the hollow fiber membrane, as shown in Figure 2. The microorganisms that have peeled off from the hollow fiber membrane are retained within the hollow fiber membrane together with the liquid S2.

[0040] <Third process> Next, the reverse flow pump 31b is stopped, the reverse flow valve 31a is closed, the first compressed air valve 521a provided in the middle of the first compressed air flow path 521 of the supply means 50 and the concentrated water valve 24a provided in the middle of the concentrated water flow path 24 are opened, the compressor 51 is driven, and compressed air is supplied to the hollow fiber membranes of the membrane module 20 via the compressed air flow path 52, the first compressed air flow path 521, and the second common flow path 23. By supplying compressed air to the hollow fiber membrane in this manner, as shown in Figure 2, the microorganisms and liquid S2 that were retained within the hollow fiber membrane and have been detached from the hollow fiber membrane are pushed out of the hollow fiber membrane as microorganism-concentrated water, and are stored and recovered in the concentrated water tank 40 via the first common flow path 22 and the concentrated water flow path 24.

[0041] <Fourth step> Next, the compressor 51 is stopped, the first compressed air valve 521a and the concentrated water valve 24a are closed, the reverse liquid flow valve 31a provided in the reverse liquid flow path 31 is opened, the reverse liquid flow pump 31b is driven, a portion of the permeate is extracted from the permeate tank 30, and the liquid is pressurized and supplied to the membrane module 20 via the reverse liquid flow path 31 and the permeate flow path 21 as liquid S3 for backwashing the hollow fiber membranes, thereby backwashing the hollow fiber membranes. At this time, the amounts of liquid S2 and liquid S4 supplied to the membrane module 20 are adjusted so that the amount of liquid S2 used for backflowing the hollow fiber membranes in the second step is less than the amount of liquid S3 used for backwashing the hollow fiber membranes in the fourth step. Furthermore, when the filtration of liquid S1 is performed using an internal pressure system in the first step, the backwashing of the hollow fiber membranes is preferably performed using an external pressure system, and when the filtration of liquid S1 is performed using an external pressure system, the backwashing of the hollow fiber membranes is preferably performed using an internal pressure system. By backwashing the hollow fiber membrane in this manner, microorganisms remaining on the hollow fiber membrane can be peeled off from the hollow fiber membrane and the surface of the hollow fiber membrane can be cleaned, as shown in Figure 2. The microorganisms peeled off from the hollow fiber membrane are retained within the hollow fiber membrane together with liquid S3.

[0042] The fourth step is a step performed after the microorganism-enriched water is extruded from the hollow fiber membrane in the third step. After all of the microorganism-enriched water retained in the hollow fiber membrane has been extruded from the hollow fiber membrane, the fourth step may be performed before the microorganism-enriched water is collected in the concentrated water tank 40, or may be performed simultaneously with the collection of the microorganism-enriched water, or may be performed after the microorganism-enriched water is collected. However, it is preferable to perform the fourth step after the microorganism-enriched water is collected. When backwashing the hollow fiber membrane, a chemical agent may be used in combination. For example, a chemical agent may be added to the liquid S3 midway through the reverse liquid flow path 31.

[0043] <Fifth step> Next, the reverse flow pump 31b is stopped, the reverse flow valve 31a is closed, the second compressed air valve 522a provided in the second compressed air flow path 522 of the supply means 50 and the first cleaning water valve 25a provided in the middle of the cleaning water waste flow path 25 are opened, the compressor 51 is driven, and compressed air is supplied to the hollow fiber membranes of the membrane module 20 via the compressed air flow path 52, the second compressed air flow path 522, and the first common flow path 22. By supplying compressed air to the hollow fiber membranes in this manner, the microorganisms and liquid S3 that were retained within the hollow fiber membranes and that have been detached from the hollow fiber membranes are discharged from the hollow fiber membranes as cleaning water, as shown in Fig. 2. The discharged cleaning water is temporarily stored in the drainage tank 60 via the second common flow path 23 and the cleaning water waste flow path 25, and then discarded.

[0044] If a large number of microorganisms remain in the hollow fiber membranes after the third step, that is, if the concentration of microorganisms in the washing water is high, the washing water may be returned to the raw water tank 10 as follows. That is, after the fourth step, the reverse flow pump 31b is stopped, the reverse flow valve 31a is closed, the second compressed air valve 522a provided in the second compressed air flow path 522 of the supply means 50 and the second cleaning water valve 26a provided in the middle of the cleaning water return flow path 26 are opened, the compressor 51 is driven, and compressed air is supplied to the hollow fiber membranes of the membrane module 20 via the compressed air flow path 52, the second compressed air flow path 522, and the first common flow path 22. By supplying compressed air to the hollow fiber membranes in this manner, the microorganisms and liquid S3 that were retained within the hollow fiber membranes and that have been detached from the hollow fiber membranes are discharged from the hollow fiber membranes as cleaning water, as shown in Figure 2. The discharged cleaning water is returned to the raw water tank 10 via the second common flow path 23 and the cleaning water return flow path 26.

[0045] In the fifth step, whether to discard the wash water or return it to the raw water tank 10 may be determined based on the concentration of microorganisms in the wash water, or on whether or not chemicals are used during backwashing of the hollow fiber membranes. For example, if the concentration of microorganisms in the wash water is low or if chemicals are used during backwashing of the hollow fiber membranes, it is preferable to discard the wash water. If the concentration of microorganisms in the wash water is high and no chemicals are used during backwashing of the hollow fiber membranes, it is preferable to return the wash water to the raw water tank 10.

[0046] [Action and effect] As described above, by performing steps (A), (B), and (C), it is possible to wash and remove not only the microorganisms accumulated on the membrane but also substances that clog the membrane. However, since a concentrated solution remains inside the membrane at the end of the filtration operation, if a large amount of backwash water is used to improve the cleaning efficiency, the concentrated solution will be diluted. Conversely, if the amount of backwash water is reduced to suppress dilution, there is a problem that the inner surface of the membrane cannot be sufficiently cleaned.

[0047] However, in the microorganism separation and recovery method and microorganism separation and recovery apparatus of this embodiment, step (B) is divided into a second step (B1) and a fourth step (B2). Specifically, in the second step (B1), a liquid S2 in an amount sufficient to detach the microorganisms is passed back through the hollow fiber membrane, so only a small amount of liquid S2 is required, minimizing dilution of the concentrated microorganism solution retained within the hollow fiber membrane. Furthermore, in the fourth step (B2), backwashing is performed with a quantity of liquid S3 sufficient to wash the membrane surface. However, the wash water after backwashing is discarded or returned to the raw water tank storing the unfiltered liquid S1, so the concentrated microorganism solution is less likely to be diluted. In addition, the present invention does not require any additional separation steps, and the increase in initial investment and running costs is extremely small. Therefore, according to the method for separating and recovering microorganisms and the apparatus for separating and recovering microorganisms of this embodiment, clogging of the hollow fiber membrane can be suppressed, and microorganisms can be stably separated and recovered at a higher concentration.

[0048] In this embodiment, the above-described membrane module 20 corresponds to a first means for filtering the liquid S1 containing microorganisms using a hollow fiber membrane to separate and concentrate the microorganisms in the liquid S1. The first means is a means for carrying out the first step. The permeate tank 30, the reverse flow path 31, the reverse flow valve 31a, the reverse flow pump 31b, and a part of the permeate flow path correspond to a second means for passing the liquid through the hollow fiber membrane in the reverse direction to separate and concentrate the microorganisms from the liquid S1 and adhere to the hollow fiber membrane, and then peeling them off from the hollow fiber membrane. The second means is a means for carrying out the second step. Furthermore, among the supply means 50, the compressor 51, the compressed air flow path 52, the first compressed air flow path 521, the first compressed air valve 521a, a part of the second common flow path 23, the first common flow path 22, the concentrated water flow path 24, the concentrated water valve 24a, and the concentrated water tank 40 correspond to a third means for supplying compressed air to the hollow fiber membranes and forcing and recovering the microorganisms detached from the hollow fiber membranes as concentrated microorganism water. The third means is a means for carrying out the third step. The permeate tank 30, the reverse flow path 31, the reverse flow valve 31a, the reverse flow pump 31b, and a part of the permeate flow path correspond to a fourth means for backwashing the hollow fiber membrane to clean the surface of the hollow fiber membrane after the microorganism-enriched water is pushed out of the hollow fiber membrane in the third means. The fourth means is a means for carrying out the fourth step. Furthermore, among the supply means 50, the compressor 51, the compressed air flow path 52, the second compressed air flow path 522, the second compressed air valve 522a, a part of the first common flow path 22, and the second common flow path 23 correspond to a fifth means that supplies compressed air to the hollow fiber membranes and discharges the wash water generated in the fourth means from the hollow fiber membranes. The fifth means is a means for carrying out the fifth step.

[0049] The method for separating and recovering microorganisms and the apparatus for separating and recovering microorganisms of the present invention are not limited to those described above. For example, compressed air may be used instead of permeated water when backflowing and backwashing the hollow fiber membrane. That is, in the second step, compressed air may be supplied to the hollow fiber membrane to separate and concentrate the microorganisms from the liquid S1 and adhere to the hollow fiber membrane, thereby peeling them off from the hollow fiber membrane. Furthermore, in the fourth step, compressed air may be supplied to the hollow fiber membrane to wash the surface of the hollow fiber membrane. In addition, a drop in the air temperature may cause a drop in the temperature inside the membrane module, which may increase the viscosity of the liquid S1 and reduce the separation performance. In such cases, the membrane module may be provided with a heating means that can heat the membrane module from the inside or outside. Furthermore, in the microorganism separation and recovery device 1 shown in Figure 1, the longitudinal direction of the hollow part of the hollow fiber membrane is vertical, and concentrated water is pushed out from the hollow fiber membrane vertically downward, and wash water is discharged from the hollow fiber membrane vertically upward, but concentrated water may also be pushed out from the hollow fiber membrane vertically upward, and wash water may also be discharged vertically downward. [Explanation of symbols]

[0050] 1. Microbial separation and recovery device 10 Raw Water Tank 11 Raw water flow path 11a Raw water valve 11b Raw water pump 20 Membrane module 21 Permeated water channel 21a Permeate valve 22 First common flow path 23 Second common flow path 24 Concentrated water flow path 24a Concentrated water valve 25 Wash water waste flow path 25a First flush water valve 26 Cleaning water return flow path 26a Second flush water valve 30 Permeation tank 31 Reverse liquid flow path 31a Reverse flow valve 31b Reverse flow pump 40 Concentrated Water Tank 50 Means of supply 51 Compressor 52 compressed air flow path 521 first compressed air flow path 521a First compressed air valve 522 Second compressed air flow path 522a Second compressed air valve 60 Drain tank S1 Liquid containing microorganisms B1 First branch point B2 Second Branching Point B3 The third branch point

Claims

1. a step of filtering a liquid S1 containing microorganisms using a hollow fiber membrane to separate and concentrate the microorganisms in the liquid S1; a step of passing the liquid S1 through the hollow fiber membrane in a reverse direction to separate and concentrate the microorganisms from the liquid S1 and adhere to the hollow fiber membrane, while washing the surface of the hollow fiber membrane; supplying compressed air to the hollow fiber membrane and recovering the microorganisms detached from the hollow fiber membrane as microorganism-enriched water, a first step of separating and concentrating the microorganisms in the liquid S1 using the hollow fiber membrane; a second step of passing the liquid S1 through the hollow fiber membrane in a reverse direction to separate and concentrate the microorganisms from the liquid S1 and adhere to the hollow fiber membrane, and then peeling the microorganisms from the hollow fiber membrane; a third step of supplying compressed air to the hollow fiber membrane to push out and recover the microorganisms detached from the hollow fiber membrane as concentrated microorganism water; A fourth step of backwashing the hollow fiber membrane after the microbially concentrated water is extruded from the hollow fiber membrane in the third step to clean the surface of the hollow fiber membrane; a fifth step of supplying compressed air to the hollow fiber membrane and discharging the cleaning water generated in the fourth step from the hollow fiber membrane; and The amount of liquid S2 used for backflow of the hollow fiber membrane in the second step is less than the amount of liquid S3 used for backwashing the hollow fiber membrane in the fourth step, In the second step, the microorganisms detached from the hollow fiber membrane are retained within the hollow fiber membrane together with the liquid S2, In the third step, the microorganisms and liquid S2 retained in the hollow fiber membrane are extruded from the hollow fiber membrane as the microorganism-enriched water and recovered.

2. The method for separating and recovering microorganisms according to claim 1 , wherein the filtration is internal pressure filtration.

3. 3. The method for separating and recovering microorganisms according to claim 1, wherein the filtration is dead-end filtration.

4. The method for separating and recovering microorganisms according to any one of claims 1 to 3, wherein the microorganisms are microalgae.

5. The method for separating and recovering microorganisms according to any one of claims 1 to 4, wherein the cleaning water is returned to a raw water tank that stores the liquid S1.

6. The method for separating and recovering microorganisms according to any one of claims 1 to 4, wherein the wash water is discarded.

7. a first means for filtering a liquid S1 containing microorganisms using a hollow fiber membrane to separate and concentrate the microorganisms in the liquid S1; a second means for passing a liquid through the hollow fiber membrane in a reverse direction to separate and concentrate microorganisms from the liquid S1 and adhere to the hollow fiber membrane, and peeling the microorganisms from the hollow fiber membrane; a third means for supplying compressed air to the hollow fiber membrane to push out the microorganisms detached from the hollow fiber membrane as concentrated microorganism water and recovering the microorganisms; A fourth means for backwashing the hollow fiber membrane after the microorganism-enriched water is extruded from the hollow fiber membrane in the third means to clean the surface of the hollow fiber membrane; a fifth means for supplying compressed air to the hollow fiber membrane and discharging the cleaning water generated by the fourth means from the hollow fiber membrane; Equipped with The amount of the liquid S2 used for backflow of the hollow fiber membrane in the second means is less than the amount of the liquid S3 used for backwashing the hollow fiber membrane in the fourth means, In the second means, the microorganisms detached from the hollow fiber membrane are retained within the hollow fiber membrane together with the liquid S2, In the third means, the microorganisms and liquid S2 retained in the hollow fiber membrane are extruded from the hollow fiber membrane as the microorganism-enriched water and recovered.

8. The apparatus for separating and recovering microorganisms according to claim 7, wherein the filtration is internal pressure filtration.

9. The apparatus for separating and recovering microorganisms according to claim 7 or 8, wherein the filtration is dead-end filtration.

10. The microorganism separation and recovery device according to any one of claims 7 to 9, wherein the microorganisms are microalgae.

11. a raw water tank for storing the liquid S1; The microorganism separation and recovery device according to any one of claims 7 to 10, further comprising a cleaning water return flow path that returns the cleaning water to the raw water tank.

12. The microorganism separation and recovery device according to any one of claims 7 to 10, further comprising a cleaning water waste flow path for discarding the cleaning water.

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