Production method for photosynthetic microorganisms and production equipment for photosynthetic microorganisms

Abstract

To provide a production method for photosynthetic microorganisms and production equipment for the photosynthetic microorganisms, each enabling the photosynthetic microorganisms to be efficiently and cost-effectively cultured and recovered.SOLUTION: A production method for photosynthetic microorganisms has: a culturing step of culturing photosynthetic microorganisms in culture solution S housed in a culture tank 11; a concentration step of membrane-filtering the culture solution S including photosynthetic microorganisms by using a separation membrane, thereby concentrating photosynthetic microorganisms; a returning step of returning at least a part of permeated water having permeated the separation membrane to the culture tank 11; and a recovery step of recovering concentrated water which has not permeated the separation membrane and in which photosynthetic microorganisms have been concentrated. Production equipment 1 for photosynthetic microorganisms comprises: a culturing means 10 culturing photosynthetic microorganisms in the culture solution S housed in the culture tank 11; concentration means 20 membrane-filtering the culture solution S including photosynthetic microorganisms by using the separation membrane, thereby concentrating photosynthetic microorganism; returning means 30 returning at least a part of the permeated water to the culture tank 11; and recovery means 40 recovering the concentrated water.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 2. Description of the Related Art In recent years, photosynthetic microorganisms, particularly microalgae, have been attracting attention as materials for biomass fuels, foods, cosmetics, and the like, and the cultivation of microalgae in large-scale plants has become common. Microalgae are usually cultured by preparing a medium in a culture tank, adding seed algae, and growing them. After the culture, a part or all of the culture solution containing the grown microalgae is extracted from the culture tank, and the microalgae are separated, concentrated, and recovered from the culture solution. When the entire culture solution is removed from the culture tank, a medium is prepared in the culture tank again and seed algae are added and grown. On the other hand, when a portion of the culture solution is removed from the culture tank, the culture tank is filled with the same amount of medium as the removed culture solution and the microalgae are grown. However, these methods require large amounts of medium components and water, which increases production costs, and also generate large amounts of waste liquid during the separation, concentration, and recovery of microalgae from the culture solution, which requires costly waste liquid treatment.

[0003] Therefore, a method for reusing the solution after culture has been proposed. For example, Patent Document 1 discloses an algae culturing method and culture device in which a culture solution after algae recovery is returned to a culture tank via an algae recovery device. Patent Document 2 discloses a method and apparatus for cultivating microalgae, in which a culture solution containing microalgae is concentrated by membrane filtration, and concentrated water containing the concentrated microalgae is returned to a culture tank, while the permeated water that has permeated through a separation membrane is returned to a culture component mixing tank installed upstream of the culture tank for mixing water and culture components of the microalgae. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-230091 A [Patent Document 2] JP 2014-76016 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the case of the method described in Patent Document 1, after the culture solution is discharged from the culture tank (and the algae are recovered), the remaining culture solution from which the algae have been recovered is returned to the culture tank via a recovery device, which is inefficient. In the method described in Patent Document 2, the permeate and concentrate can be returned efficiently, but the culture efficiency is likely to decrease. An object of the present invention is to provide a method and an apparatus for producing photosynthetic microorganisms, which are capable of culturing and recovering photosynthetic microorganisms efficiently at low cost. [Means for solving the problem]

[0006] As a result of intensive research, the inventors have found that when concentrated water containing concentrated microalgae is returned to the culture tank, impurities such as bacteria and organic matter that did not permeate the separation membrane are also returned to the culture tank together with the microalgae, resulting in a decrease in culture efficiency. Therefore, the inventors have found that by concentrating the culture solution using a separation membrane, returning the permeated water to the culture tank while recovering the concentrated water, it is possible to culture and recover photosynthetic microorganisms efficiently at low cost, and have completed the present invention.

[0007] That is, the present invention has the following aspects. [1] A cultivation step of culturing photosynthetic microorganisms in a culture solution contained in a culture tank; A concentration step of filtering the culture solution containing the photosynthetic microorganisms using a separation membrane to concentrate the photosynthetic microorganisms; A returning step of returning at least a portion of the permeate that has permeated the separation membrane to the culture tank; A recovery step of recovering concentrated water that does not permeate the separation membrane and in which the photosynthetic microorganisms are concentrated; The method for producing a photosynthetic microorganism comprising the steps of: [2] The method for producing a photosynthetic microorganism according to [1] above, further comprising a preparation step of preparing a medium for the culture solution contained in the culture tank. [3] The method for producing photosynthetic microorganisms according to [1] or [2] above, wherein the nominal pore size of the micropores formed in the separation membrane is 5 μm or less. [4] The method for producing a photosynthetic microorganism according to any one of [1] to [3] above, wherein the permeate has a dissolved organic carbon concentration of 20 mg / L or less. [5] The method for producing a photosynthetic microorganism according to any one of [1] to [4] above, wherein the photosynthetic microorganism is a microalgae.

[0008] [6] A culture means for culturing photosynthetic microorganisms in a culture solution contained in a culture tank; A concentration means for concentrating the photosynthetic microorganisms by membrane filtering the culture solution containing the photosynthetic microorganisms using a separation membrane; A return means for returning at least a portion of the permeate that has permeated the separation membrane to the culture tank; a recovery means for recovering concentrated water that does not permeate the separation membrane and in which the photosynthetic microorganisms are concentrated; A photosynthetic microorganism production apparatus comprising: [7] The apparatus for producing photosynthetic microorganisms according to [6], further comprising a preparation means for preparing a medium in the culture solution contained in the culture tank. [8] The apparatus for producing photosynthetic microorganisms according to [6] or [7], wherein the nominal pore size of the micropores formed in the separation membrane is 5 μm or less. [9] The apparatus for producing photosynthetic microorganisms according to any one of [6] to [8] above, wherein the concentration of dissolved organic carbon in the permeate is 20 mg / L or less.

[10] The apparatus for producing a photosynthetic microorganism according to any one of [6] to [9] above, wherein the photosynthetic microorganism is a microalgae. Effect of the Invention

[0009] According to the present invention, it is possible to provide a method and an apparatus for producing photosynthetic microorganisms, which are capable of culturing and recovering photosynthetic microorganisms efficiently at low cost. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an example of an apparatus for producing photosynthetic microorganisms according to the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing another example of an apparatus for producing photosynthetic microorganisms according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of a method and an apparatus for producing a photosynthetic microorganism according to the present invention will be described in detail below with reference to Figs. In addition, in each drawing used in the following description, characteristic parts 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 thereto, and can be appropriately changed and implemented within the scope of the present invention. In addition, in FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

[0012] [Photosynthetic microorganism production equipment] FIG. 1 shows an example of an apparatus for producing photosynthetic microorganisms according to the present invention. The apparatus 1 for producing photosynthetic microorganisms shown in FIG. 1 includes a culture means 10, a concentration means 20, a return means 30, a recovery means 40, and a preparation means 50.

[0013] <Culture means> The culture means 10 is a means for culturing photosynthetic microorganisms in a culture solution S contained in a culture tank 11. The culture means 10 shown in FIG. 1 includes a culture tank 11 for storing a culture solution S, and a culture solution flow path 12 for supplying the culture solution S to a concentration means 20.

[0014] As the culture tank 11, a closed culture tank may be used when the photosynthetic microorganisms are cultured in a closed system, and an open culture tank may be used when the photosynthetic microorganisms are cultured in an open system. An example of a closed culture tank is a photobioreactor tank. Photobioreactor tanks include semi-closed tanks and closed tanks, and specific examples include flat-plate tanks, tube tanks, solar light collecting tanks, and internal irradiation tanks. An example of an open culture tank is an open pond type tank. A specific example of an open pond type tank is a raceway type tank. Instead of the culture tank 11, photosynthetic microorganisms may be cultured in a pond or the like. Furthermore, the culture tank 11 may be a hybrid tank in which the photosynthetic microorganisms can be cultured in both an open system and a closed system.

[0015] The culture solution S contains photosynthetic microorganisms and a culture medium, and is the raw water to be concentrated. The photosynthetic microorganism to be cultured is not particularly limited as long as it is a microorganism that performs photosynthesis and can be appropriately selected depending on the purpose, and examples thereof include microalgae and photosynthetic bacteria. Among these, microalgae are preferred because they are useful as biomass fuels, and as materials for foods, cosmetics, and the like.

[0016] Microalgae are single-celled organisms with photosynthetic capabilities, with a body length (longest diameter of the cell) of 100 μm or less. Examples of microalgae include, but are not limited to, the genus Euglena (green algae), the genus Coccomyxa, the genus Nannochloropsis, the genus Microchloropsis, blue-green algae, prokaryotic green algae, red algae, glaucophytes, cryptophytes, dinoflagellates, golden algae, diatoms, brown algae, xanthophytes, haptophytes, raphidophytes (green algae), chlorarachniophytes, prasinophytes, green algae, and charophytes. Among these, the genus Euglena, the genus Coccomyxa, the genus Nannochloropsis, the genus Microchloropsis, and spirulina, a type of blue-green algae, are preferred from the viewpoint of containing many nutrients and being suitable for use in foods, cosmetics, and the like. The photosynthetic bacteria are not particularly limited, but examples thereof include purple bacteria, green non-sulfur bacteria, green sulfur bacteria, and heliobacteria.

[0017] The culture solution flow path 12 is a pipe that extracts a portion of the culture solution S from the culture tank 11 and supplies the extracted culture solution S to the concentrating means 20. One end of the culture solution flow path 12 is connected to the culture tank 11, and the other end is connected to a concentrating tank 21 of the concentrating means 20, which will be described later. A raw water pump P1 is installed in the middle of the culture solution flow path 12. The raw water pump P1 is a means for extracting the culture solution S stored in the culture tank 11 from the culture tank 11 and supplying it under pressure to the concentration tank 21. There are no particular limitations on the raw water pump P1 as long as it can supply the culture solution S to the concentration tank 21 under pressure.

[0018] <Concentration means> The concentrating means 20 is a means for concentrating the photosynthetic microorganisms by membrane filtering the culture solution S containing the photosynthetic microorganisms using a separation membrane. The concentrating means 20 of this embodiment can also be said to be a membrane filtering means for the photosynthetic microorganisms. The concentrating means 20 shown in FIG. 1 includes a concentrating tank 21 and a membrane module 22 including a separation membrane. A culture solution flow path 12 is connected to the concentration tank 21, and the culture solution S is supplied from the culture means 10 to the concentration tank 21.

[0019] The membrane module 22 is disposed in the concentration tank 21 and is immersed in the culture solution S supplied from the culture means 10 . The membrane module 22 is a means for separating the culture solution S introduced into a separation membrane through membrane filtration into a permeate that has permeated the separation membrane and a concentrated water that has not permeated the separation membrane and is concentrated with photosynthetic microorganisms. In the membrane module 22, the culture solution S is filtered through a separation membrane and concentrated.

[0020] The form of the membrane module 22 is not particularly limited, but may include, for example, a sheet-like material in which a plurality of separation membranes are arranged at a fixed interval, and a pair of housings that support the sheet-like material. Note that a plurality of separation membranes may be bundled together to form a separation membrane bundle, and the separation membrane bundles may be arranged at a fixed interval to form the sheet-like material.

[0021] Examples of the separation membrane include a microfiltration membrane and an ultrafiltration membrane. In addition, in the case of laboratory-scale experiments, a syringe filter may be used. The nominal pore size of the micropores formed in the separation membrane is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 2 μm or less, particularly preferably 0.45 μm or less, and most preferably 0.4 μm or less. The nominal pore size of the micropores is preferably 0.02 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. If the nominal pore size of the micropores is equal to or greater than the above lower limit, clogging can be suppressed and separation efficiency can be maintained at a good level. In addition, the pressure required for solid-liquid separation can be sufficiently suppressed. If the nominal pore size of the micropores is equal to or less than the above upper limit, photosynthetic microorganisms are less likely to leak into the permeate. In addition, impurities in the culture solution S, which are a source of contamination, are less likely to leak into the permeate. Therefore, the permeate from which impurities have been sufficiently removed can be returned to the culture tank 11, and the decrease in culture efficiency can be further suppressed. Here, impurities include unintended photosynthetic microorganisms that compete with the cultured photosynthetic microorganisms for light and nutrients, zooplankton that are fed on the cultured photosynthetic microorganisms, microorganisms other than photosynthetic microorganisms that block light by multiplying, and other bacteria (excluding photosynthetic bacteria) that can be sources of contamination (hereinafter also referred to as "contaminating microorganisms"); proteins and polysaccharides secreted by photosynthetic microorganisms, sugars and other components that serve as nutrients for microorganisms, humic substances, organic matter such as the corpses of microorganisms, etc.

[0022] In addition, the nominal pore size is, in the case of a microfiltration membrane, the particle size at which the rejection rate of latex particles of each particle size is measured and calculated from the approximation curve of particle size and rejection rate at 90%, and in the case of an ultrafiltration membrane, the Stokes diameter at which the rejection rate of dextran of each Stokes diameter is measured and calculated from the approximation curve of Stokes diameter and rejection rate at 90%. When a commercially available product is used as the separation membrane, the catalog value may be used as the nominal pore size.

[0023] Examples of the form of the separation membrane include hollow fiber membranes, tubular membranes (tubular membranes, single-bore type, multi-bore type, etc.), spiral membranes, flat membranes, and monolithic membranes. Among these, hollow fiber membranes and tubular membranes are preferred because of their high volumetric filling rate. When using a monolithic membrane as the separation membrane, it is preferred to use a ceramic membrane.

[0024] When a hollow fiber membrane is used as the separation membrane of the membrane module 22, examples of the material include cellulose, polyolefin, polysulfone, polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). Among these, PVDF, PTFE, and PES are preferable as the material for the hollow fiber membrane because of their resistance to chemicals and pH changes. The outer diameter of the hollow fiber membrane is preferably from 0.01 to 3 mm, more preferably from 0.05 to 1 mm. The inner diameter of the hollow fiber membrane is preferably 0.005 mm or more and less than 1 mm. The outer diameter of a hollow fiber membrane means the diameter of the smallest circle inscribed on the outer edge of a cut surface when the hollow fiber membrane is cut along an arbitrary plane perpendicular to the longitudinal direction, and is calculated as the average value of measurements taken at any 2 to 10 locations. The inner diameter of a hollow fiber membrane means the diameter of the smallest circle inscribed on the inner edge of a cut surface when the hollow fiber membrane is cut along an arbitrary plane perpendicular to the longitudinal direction, and is calculated as the average value of measurements taken at any 2 to 10 locations.

[0025] When a tubular membrane is used as the separation membrane of the membrane module 22, examples of the material include polyolefin, PVDF, PTFE, polystyrene, polyacrylonitrile, cellulose acetate, polysulfone, PES, and ceramics. Among these, PVDF, PTFE, and PES are preferred as the material for the tubular membrane because of their excellent chemical resistance and processability into a membrane module. The inner diameter of the tubular membrane is preferably 1 mm or more, and is preferably 10 mm or less, more preferably 5 mm or less, more preferably 3 mm or less, even more preferably less than 3 mm, and particularly preferably 2 mm or less. The inner diameter of a tubular membrane means the diameter of the smallest circle inscribed on the inner edge of a cut surface perpendicular to the longitudinal direction of the tubular membrane, and is calculated as the average value of measurements taken at any two or more but no more than ten points. In the case of a multi-bore type tubular membrane, the average value of the inner diameters at any one or more points is taken as the inner diameter of the tubular membrane.

[0026] <Return method> The return means 30 is a means for returning at least a part of the permeate that has permeated the separation membrane to the culture tank 11. In the return means 30 of the present embodiment, the entire amount of the permeate is returned to the culture tank 11. The return means 30 shown in FIG.

[0027] The permeate flow path 31 is a pipe that discharges the permeate that has permeated through the separation membrane of the membrane module 22, i.e., the separated liquid in which photosynthetic microorganisms and the like have been removed from the culture solution S, from the membrane module 22, and returns it to the culture tank 11. One end of the permeate flow path 31 is connected to the membrane module 22, and the other end is connected to the culture tank 11. A first suction pump P3 is installed in the permeate flow path 31. The first suction pump P3 is a means for sucking the permeate that has permeated through the separation membrane of the membrane module 22 and discharging it from the membrane module 22. There are no particular limitations on the first suction pump P3 as long as it can suck the permeate.

[0028] <Method of recovery> The recovery means 40 is a means for recovering concentrated water that does not pass through the separation membrane and in which photosynthetic microorganisms are concentrated. The recovery means 40 recovers the concentrated water without returning it to the culture tank 11. The recovery means 40 shown in FIG.

[0029] The concentrated water flow path 41 is a pipe that discharges concentrated water in which photosynthetic microorganisms are concentrated and that does not pass through the separation membrane of the membrane module 22 from the concentration tank 21. One end of the concentrated water flow path 41 is connected to the concentration tank 21, and the other end is connected to, for example, a recovery tank (not shown) that stores the concentrated water. A second suction pump P4 is installed in the concentrated water flow path 41. The second suction pump P4 is a means for sucking the concentrated water in which the photosynthetic microorganisms are concentrated, and discharging it from the concentration tank 21. There are no particular limitations on the second suction pump P4, so long as it can suck up the concentrated water.

[0030] The concentrated water discharged from the concentration tank 21 is recovered and used for various purposes, such as biomass fuel or as a material for food, cosmetics, etc. Impurities in the culture solution S that did not pass through the separation membrane will also be recovered together with the photosynthetic microorganisms. However, after recovery, the impurities can be removed by extracting, purifying, or modifying the photosynthetic microorganisms as necessary.

[0031] <Preparation means> The preparation means 50 is a means for preparing the medium in the culture solution S contained in the culture tank 11. The preparation means 50 shown in FIG. 1 includes a tank 51 that contains a novel liquid medium used for culturing photosynthetic microorganisms, and a medium flow path 52. A novel liquid culture medium is contained in tank 51. Materials for the liquid culture medium are not particularly limited, but examples thereof include seawater, lake water, river water, and tap water.

[0032] The culture medium flow path 52 is a pipe that supplies the new liquid culture medium contained in the tank 51 to the culture solution S contained in the culture tank 11. The culture medium flow path 52 in the illustrated example has one end connected to the tank 51 and the other end connected to the permeate flow path 31, so that a new liquid culture medium can be added to the permeate in the permeate flow path 31 to prepare the culture medium. At least one of the permeate flow path 31 and the culture tank 11 is preferably provided with a concentration meter (not shown) for measuring the concentration of the medium.

[0033] [Production method of photosynthetic microorganisms] An example of the method for producing a photosynthetic microorganism of the present invention will be described below. Note that the method for producing a photosynthetic microorganism described below is an example of the method for producing a photosynthetic microorganism using an apparatus 1 for producing a photosynthetic microorganism shown in FIG. The method for producing photosynthetic microorganisms of this embodiment includes the following culturing step, concentrating step, returning step, recovering step, and preparing step.

[0034] <Culture process> The culturing step is a step of culturing photosynthetic microorganisms in the culture solution S contained in the culture tank 11. After the concentration of photosynthetic microorganisms in the culture solution S reaches a set value, the raw water pump P1 installed in the culture solution flow path 12 is driven to extract a portion of the culture solution S containing the cultured photosynthetic microorganisms from the culture tank 11 and supply it to the concentration tank 21.

[0035] <Concentration process> The concentration step is a step of subjecting the culture solution S containing the photosynthetic microorganisms to membrane filtration using a separation membrane to concentrate the photosynthetic microorganisms. Specifically, the first suction pump P3 is operated to reduce the pressure inside the membrane module 22, whereby the culture solution S is subjected to membrane filtration to be separated into permeate and concentrated water. At this time, membrane filtration may be performed while diffusing air or the like by an aeration means (not shown) installed below the membrane module 22. By diffusing air or the like, it is possible to efficiently perform membrane filtration while cleaning the surface of the separation membrane (e.g., hollow fiber membrane or the like) of the membrane module 22.

[0036] <Return process> The returning step is a step of returning at least a portion of the permeate that has permeated the separation membrane to the culture tank 11. The permeate that has permeated the separation membrane of the membrane module 22 is discharged from the membrane module 22 through the permeate flow path 31 and returned to the culture tank 11. In the case of the illustrated example of the photosynthetic microorganism production apparatus 1, the entire amount of the permeate is returned to the culture tank 11. The permeate contains unused medium, that is, nutrients that remain unused in the culture, so that the permeate can be reused for the culture by returning it to the culture tank 11.

[0037] The dissolved organic carbon (DOC) concentration of the permeate returned to the culture tank 11 is preferably 20 mg / L or less, more preferably 18 mg / L or less, and even more preferably 15 mg / L or less. In the concentration tank 21, photosynthetic microorganisms may secrete proteins and polysaccharides, and dead cells may release DOC. If this DOC permeates the separation membrane and is returned to the culture tank 11 together with the permeate, bacteria and the like may grow by feeding on the returned DOC, which may hinder the growth of the photosynthetic microorganisms. If the DOC concentration in the permeate is equal to or lower than the upper limit, the photosynthetic microorganisms can be cultured more efficiently without hindering their growth.

[0038] The DOC concentration of the permeate can be controlled, for example, by the nominal pore size of the micropores formed in the separation membrane, and the smaller the nominal pore size of the micropores formed in the separation membrane, the lower the DOC concentration of the permeate tends to be. For example, by using a separation membrane in which micropores with a nominal pore size of 5 μm or less are formed, the DOC concentration of the permeate can be easily controlled to 20 mg / L or less. The DOC concentration of the permeate can be determined, for example, by removing inorganic carbon from the permeate and then measuring the concentration of carbon dioxide generated by burning organic matter.

[0039] <Recovery process> The recovery step is a step of recovering concentrated water that does not pass through the separation membrane and in which photosynthetic microorganisms are concentrated. Specifically, the second suction pump P4 is operated to periodically discharge and recover concentrated water from the concentration tank 21 via the concentrated water flow path 41.

[0040] <Preparation process> The preparation step is a step of preparing the medium in the culture solution S contained in the culture tank 11. For example, when the amount of culture solution S contained in the culture tank 11 is small, a new liquid medium contained in the tank 51 is added to the permeate in the permeate flow path 31 via the medium flow path 52. In addition, the concentration of the culture medium in the permeate passing through the permeate flow path 31 or the concentration of the culture medium in the culture solution S contained in the culture tank 11 may be measured, and if the concentration is low, a new liquid culture medium may be added to the permeate in the permeate flow path 31. Here, the concentration of the medium refers to the concentration of a compound in the culture solution S, which contains one or more compounds selected from nitrogen, phosphorus, vitamins, and potassium.

[0041] [Effects] In the method and apparatus for producing photosynthetic microorganisms according to the present embodiment described above, the permeate that permeates the separation membrane, which is generated when concentrating the culture solution containing photosynthetic microorganisms using a separation membrane after the culture, is returned to the culture tank, and the permeate is reused for culture. The permeate contains unused medium, i.e., nutrients that remain unused in the culture, and is therefore suitable for reuse. By reusing the permeate for culture, the amount of new medium and water required for medium preparation can be reduced, and photosynthetic microorganisms can be cultured at low cost and with low energy consumption. In addition, while disposal of the permeate is expensive, the permeate is reused for culture in the present embodiment, and therefore the cost of treating the permeate can also be reduced. Moreover, in this embodiment, since the permeate is returned directly to the culture tank, there is no need to install a culture component mixing tank for mixing water and culture components upstream of the culture tank, and a space-saving facility can be realized.

[0042] In addition, as described above, when the concentrated water is returned to the culture tank, impurities that did not permeate the separation membrane are also returned to the culture tank, resulting in a decrease in the culture efficiency, but in this embodiment, the concentrated water that does not permeate the separation membrane and is concentrated with photosynthetic microorganisms is collected without being returned to the culture tank. Therefore, even if impurities are contained in the concentrated water, the impurities are collected together with the photosynthetic microorganisms, so that the impurities are less likely to be returned to the culture tank, and a decrease in the culture efficiency can be suppressed. Moreover, in this embodiment, the culture solution containing photosynthetic microorganisms is filtered through a separation membrane to simultaneously obtain permeate and concentrate, and the permeate is returned to the culture tank and the concentrate is recovered. Therefore, the return of the permeate and the recovery of the concentrate can be performed more efficiently than in the case where the culture solution remaining in the culture tank is returned to the culture tank via a recovery device after the culture solution is discharged (recovered) from the culture tank. In this way, the method and apparatus for producing photosynthetic microorganisms according to this embodiment makes it possible to culture and recover photosynthetic microorganisms efficiently and at low cost.

[0043] Although the photosynthetic microorganism production apparatus 1 shown in FIG. 1 is provided with one culture tank 11, a plurality of culture tanks may be provided to simultaneously culture photosynthetic microorganisms. 1 returns the entire amount of the permeated water obtained in the concentration means 20 to the culture tank 11, but a part of the permeated water may be returned to the culture tank 11. In this case, the remaining permeated water that is not returned to the culture tank 11 may be discarded or used as a backwash liquid for backwashing the separation membrane. In addition, in the preparation means 50 shown in FIG. 1, the culture medium flow path 52 is connected to the permeate flow path 31, and the culture medium is prepared before being returned to the culture tank 11. However, the culture medium flow path 52 may be connected to the culture tank 11, and a new liquid culture medium may be added to the culture solution S contained in the culture tank 11.

[0044] In addition, in the photosynthetic microorganism production apparatus 1 shown in Figure 1, the membrane module 22 provided in the concentration means 20 is of an immersion type and performs membrane filtration using the out-in method, but for example, as in the photosynthetic microorganism production apparatus 2 shown in Figure 2, the membrane module 23 provided in the concentration means 20 may be of a pressurized type and perform membrane filtration of the culture solution S.

[0045] The concentrating means 20 shown in FIG. 2 includes a membrane module 23 that includes a separation membrane. The membrane module 23 is a means for separating the culture solution S introduced into a separation membrane through membrane filtration into a permeate that has permeated the separation membrane and a concentrated water that does not permeate the separation membrane and is concentrated with photosynthetic microorganisms. Examples of the separation membrane provided in the membrane module 23 include the separation membranes exemplified above in the description of the membrane module 22 shown in Fig. 1. Among them, hollow fiber membranes and tubular membranes are preferable.

[0046] The membrane module 23 shown in Fig. 2 is a pressurized type for filtration. 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. Here, the internal pressure type refers to a filtration method (in-out type) in which, for example, when the separation membrane has a hollow portion such as a hollow fiber membrane or a tubular membrane, the feed water is passed inside the hollow fiber membrane or the tubular membrane and the permeated water is obtained on the outside. The external pressure type refers to a filtration method (out-in type) in which the feed water is passed outside the hollow fiber membrane or the tubular membrane and the permeated water is obtained on the inside.

[0047] A culture medium flow path 12 is connected to the membrane module 23 , and the culture medium S is supplied from the culture means 10 to the membrane module 23 . In addition, a permeate flow path 31 is connected to the membrane module 23 so that the permeate that has permeated the separation membrane can be discharged from the membrane module 23. In addition, a concentrated water flow path 41 is connected to the membrane module 23, so that concentrated water that did not pass through the separation membrane and in which photosynthetic microorganisms are concentrated can be discharged from the membrane module 23.

[0048] The method for producing photosynthetic microorganisms using the photosynthetic microorganism production apparatus 2 shown in Figure 2 includes a culture process, a concentration process, a return process, a recovery process, and a preparation process, and is the same as the method for producing photosynthetic microorganisms using the photosynthetic microorganism production apparatus 1 shown in Figure 1, except that the culture solution S is filtered under pressure in the concentration process. EXAMPLES

[0049] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Various modifications of the embodiment of the present invention are possible as long as they do not deviate from the gist of the present invention.

[0050] [Example 1] Photosynthetic microorganisms were produced using the production apparatus 1 shown in FIG. 1 as follows. The membrane module 22 was a submerged hollow fiber membrane module (manufactured by Mitsubishi Chemical Corporation, product name "50E0006SM", nominal pore size 0.4 μm, membrane outer diameter 2.8 mm, membrane area 6 m 2 ) were used. The liquid medium used was Cramer and Myers medium (CM medium).

[0051] First, as a photosynthetic microorganism, the microalgae Euglena was cultured in a liquid medium with a pH adjusted to 2.5 to 3.5 in a culture tank 11 installed outdoors where sunlight was available. The outdoor conditions and the concentration of the microalgae were as follows. Outdoor conditions: Average daytime water temperature is within the range of 15-35°C, and the monthly average of global solar radiation is 9-20MJ / m 2 . Microalgae concentration: 800mg / L.

[0052] Next, the raw water pump P1 was driven to extract a part of the culture solution S from the culture tank 11 and supply it to the concentration tank 21. The suction pump P2 was operated to reduce the pressure inside the membrane module 22, and the culture solution S was subjected to membrane filtration to separate it into permeate and concentrated water. The average membrane filtration flux of the culture solution S at this time was set to 0.6 m / d. The entire amount of permeate that permeated the separation membrane of the membrane module 22 was discharged from the membrane module 22 via the permeate flow path 31 and returned to the culture tank 11. The second suction pump P4 was driven, and the concentrated water that did not pass through the separation membrane of the membrane module 22 and was concentrated with photosynthetic microorganisms was periodically discharged from the concentration tank 21 through the concentrated water flow path 41 so that the water in the concentration tank 21 was concentrated 10 times, and then recovered.

[0053] A portion of the permeate returned to the culture tank 11 was sampled, and the light loss, DOC concentration, and dissolved nitrogen (DN) concentration were measured by the following measurement methods to evaluate the inclusion of contaminating microorganisms and the proliferation of the contaminating microorganisms. These results are shown in Table 1. The "contaminating microorganism" refers to a microorganism that can be a source of contamination. Specifically, it includes the microorganisms exemplified earlier as impurities in the description of the separation membrane.

[0054] <Measurement of light loss> Using a turbidimeter (manufactured by AS ONE Corporation, model number "TN100IR"), the light loss was measured with the turbidity of the unused medium as the denominator and the turbidity of the permeated water as the numerator. The lower the light loss, the fewer impurities there are in the permeated water.

[0055] <Measurement of DOC concentration> After filtering the permeated water with a syringe filter having a pore size of 0.45 μm, the total organic carbon was measured using a TOC·TN meter (manufactured by Shimadzu Corporation, model "TOC-V" CPN "), and the DOC concentration was determined. The lower the DOC concentration in the permeated water, the less organic matter such as sugar permeates through the separation membrane, which means that the permeated water with sufficient removal of the organic matter that serves as nutrients for contaminating microorganisms can be returned to the culture tank.

[0056] <Measurement of DN concentration> After filtering the permeated water with a syringe filter having a pore size of 0.45 μm, the total nitrogen was measured using a TOC·TN meter (manufactured by Shimadzu Corporation, model "TOC-V" CPN "), and the DN concentration was determined. The higher the DN concentration in the permeated water, the more nutrients permeate through the separation membrane, which means that the permeated water containing a large amount of nutrients can be returned to the culture tank.

[0057] <Evaluation of contamination by contaminating microorganisms> The permeated water was examined using an optical microscope to observe the abundance of microorganisms other than green algae (contaminating microorganisms), and the presence or absence of detection of contaminating microorganisms was evaluated.

[0058] [Example 2] Using the photosynthetic microorganism production apparatus 2 shown in Fig. 2, photosynthetic microorganisms were produced as follows. The membrane module 23 was an internal pressure pressurized membrane module (manufactured by DuPont, product name “dizzerXL 1.5MB40W”, inner diameter 1.5 mm, membrane area: 40 m 2 A multi-bore tubular membrane was used. The liquid medium used was Cramer and Myers medium (CM medium).

[0059] First, as a photosynthetic microorganism, the microalgae Euglena was cultured in a liquid medium in a culture tank 11 installed outdoors where sunlight was available. The outdoor conditions and the concentration of the microalgae were as follows. Outdoor conditions: Average daytime water temperature is within the range of 15-35°C, and the monthly average of global solar radiation is 9-20MJ / m 2 . Microalgae concentration: 800mg / L.

[0060] Next, the raw water pump P1 was driven to extract a part of the culture solution S from the culture tank 11 and supply it to the concentration tank 21. The suction pump P2 was operated to pressurize the inside of the membrane module 23, and the culture solution S was subjected to membrane filtration to separate it into permeate and concentrated water. The average membrane filtration flux of the culture solution S at this time was set to 0.7 m / d. The entire amount of permeate that permeated the separation membrane of the membrane module 23 was discharged from the membrane module 23 via the permeate flow path 31 and returned to the culture tank 11. The second suction pump P4 was driven, and the concentrated water that did not pass through the separation membrane of the membrane module 23 and was concentrated with photosynthetic microorganisms was periodically discharged from the membrane module 23 through the concentrated water flow path 41 so that the water inside the membrane module 23 was concentrated 10 times, and then recovered.

[0061] A portion of the permeate returned to the culture tank 11 was collected, and various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0062] [Comparative Example 1] Photosynthetic microorganisms were cultured in the same manner as in Example 1. The culture solution S containing the cultured photosynthetic microorganisms was centrifuged using a centrifuge. A portion of the supernatant after centrifugation was collected and subjected to various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 1.

[0063] [Table 1]

[0064] As is clear from the results in Table 1, the permeate that passed through the separation membrane contained the same amount of nutrients as the supernatant obtained by centrifugation, but contained fewer impurities than the supernatant due to less light loss. Furthermore, in the cases of Examples 1 and 2, no contaminating microorganisms were detected in the permeated water, but in the case of Comparative Example 1, contaminating microorganisms were detected in the supernatant. It is generally said that contaminating microorganisms grow when organic matter is present, but do not grow when organic matter is absent. Also, the more organic matter there is, the more likely the contaminating microorganisms tend to grow. In the cases of Examples 1 and 2, the DOC concentration in the permeate was 20 mg / L or less, so it is presumed that the growth of contaminating microorganisms was suppressed compared to Comparative Example 1. These results show that the present invention allows the permeate containing nutrients to be returned to the culture tank and reused for culture, and furthermore, the permeate contains a small amount of impurities such as contaminating microorganisms and organic matter, thereby suppressing a decrease in culture efficiency.

[0065] [Example 3] A medium containing microorganisms was prepared using a photosynthetic microorganism production apparatus (not shown) consisting of an air supply device and a water tank (culture tank) in the following steps. Step 1-1: 700 mL of Daigo IMK medium (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared and poured into the culture tank. Step 1-2: The N. gaditana culture solution was inoculated into the medium prepared in step 1 above so as to give a concentration of 500 mg / L. Steps 1-3: Air (1 vol% CO) at 0.7 L / min 2 The medium was aerated with 0.1% NaCl and incubated at room temperature (25-30°C) in natural light for 3 weeks. Step 1-4: After step 1-3, 250 mL of the culture medium in the culture tank was set aside, and the remaining culture medium was centrifuged at 6,000 rpm for 1 minute to collect the supernatant (hereinafter referred to as the "centrifugation supernatant"). Step 1-5: Of the centrifugal supernatant collected in step 1-4, 70 mL was collected and set aside. Step 1-6: Using five types of syringe filters with pore sizes of 3 μm, 1 μm, 0.45 μm, 0.2 μm, and 0.1 μm, 70 mL of the remaining centrifugal supernatant was filtered. The obtained filtrates were called 3 μm filtrate, 1 μm filtrate, 0.45 μm filtrate, 0.2 μm filtrate, and 0.1 μm filtrate, respectively.

[0066] Next, in order to simulate an evaluation of the effect of having a return means (return process) using the prepared medium containing the microorganisms, i.e., the culture solution set aside in steps 1-4, the microorganisms were cultured (produced) in the steps shown below, and the culture solution was then collected and the concentration of the microalgae was measured as follows. The results are shown in Table 2. The concentrations of microalgae shown in Table 2 are relative values ​​(relative concentrations) of the concentration of microalgae in the culture solution 5 days after the start of culture, assuming that the concentration of microalgae in the culture solution at the start of culture is 1. Step 2-1: 70 mL of each of the filtrates obtained in step 1-6 (3 μm filtrate, 1 μm filtrate, 0.45 μm filtrate, 0.2 μm filtrate, and 0.1 μm filtrate) was poured into separate culture tanks. Step 2-2: 0.2 mL of Hyponica liquid fertilizer (Kyowa Co., Ltd.) was added to each culture tank. Step 2-3: 30 mL of the culture liquid set aside in step 1-4 was inoculated into each culture tank. Steps 2-4: Air (1 vol% CO) at 0.1 L / min 2 (containing PPFD: 140 μmol / m 2 The cells were cultured at room temperature (25-30°C) for 5 days while being exposed to a 14-hr ON / 10-hr OFF light (14 hrs ON / 10 hrs OFF).

[0067] <Measurement of microalgae concentration> 10 mL of the obtained microalgae culture solution was filtered by suction using a glass filter (manufactured by Advantec Toyo Co., Ltd., product name "GS-25"), and washed with 30 mL of pure water while continuing suction. The glass filter was then dried overnight at 105°C and weighed, and the weight of the microalgae per volume of the culture solution was calculated to obtain the concentration of the microalgae in the culture solution.

[0068] [Comparative Example 2] The microorganisms were cultured and the concentration of microalgae was measured in the same manner as in Example 3, except that in step 2-1, 70 mL of the centrifugal supernatant set aside in step 1-5 was used instead of the filtrate. The results are shown in Table 2.

[0069] [Reference example A] In step 2-1, except that a new medium, i.e., 70 mL of Daigo IMK medium, was used instead of the filtrate, the microorganisms were cultured in the same manner as in Example 3, and the concentration of microalgae was measured. The results are shown in Table 2.

[0070] [Table 2]

[0071] As is clear from the results in Table 2, when microalgae were cultured using a medium containing the same type of microalgae, the concentration of microalgae in the culture medium 5 days after the start of culture was clearly higher when the filtrate obtained by filtering the centrifugation supernatant through a syringe filter was used for culturing the microalgae (Example 3 in which the return means (return process) was simulated and evaluated) than when the centrifugation supernatant was used for culturing the microalgae without filtering (Comparative Example 2). Furthermore, in Example 3, the concentration of microalgae in the culture medium 5 days after the start of culture was approximately the same as or slightly lower than when a new medium was used for culturing the microalgae (Reference Example A). These results indicate that microalgae can be actively cultivated by reusing the medium through a syringe filter (or a membrane with the same nominal pore size). [Explanation of symbols]

[0072] 1. Photosynthetic microorganism production equipment 2. Photosynthetic microorganism production equipment 10 Culture means 11 Culture tank 12 Culture medium flow path 20 Concentration means 21 Concentrator 22 Membrane module 23 Membrane Module 30 Return Method 31 Permeated water channel 40 Recovery Methods 41 Concentrated water flow path 50 Preparation means 51 Tank 52 Culture medium flow path S culture solution P1 Raw water pump P3 First suction pump P4 Secondary suction pump

Claims

1. A culturing step of culturing photosynthetic microorganisms in a culture solution contained in a culture tank; A concentration step of filtering the culture solution containing the photosynthetic microorganisms using a separation membrane to concentrate the photosynthetic microorganisms; A returning step of returning at least a portion of the permeate that has permeated the separation membrane to the culture tank; A recovery step of recovering concentrated water that does not permeate the separation membrane and in which the photosynthetic microorganisms are concentrated; The method for producing a photosynthetic microorganism comprising the steps of:

2. The method for producing photosynthetic microorganisms according to claim 1 , further comprising a preparation step of preparing a medium for the culture solution contained in the culture tank.

3. The method for producing photosynthetic microorganisms according to claim 1 or 2, wherein the nominal pore size of the micropores formed in the separation membrane is 5 μm or less.

4. 3. The method for producing photosynthetic microorganisms according to claim 1, wherein the concentration of dissolved organic carbon in the permeate is 20 mg / L or less.

5. The method for producing a photosynthetic microorganism according to claim 1 or 2, wherein the photosynthetic microorganism is a microalgae.

6. A culture means for culturing photosynthetic microorganisms in a culture solution contained in a culture tank; A concentration means for concentrating the photosynthetic microorganisms by membrane filtering the culture solution containing the photosynthetic microorganisms using a separation membrane; A return means for returning at least a portion of the permeate that has permeated the separation membrane to the culture tank; a recovery means for recovering concentrated water that does not permeate the separation membrane and in which the photosynthetic microorganisms are concentrated; A photosynthetic microorganism production apparatus comprising:

7. 7. The apparatus for producing photosynthetic microorganisms according to claim 6, further comprising a preparation means for preparing a medium in the culture solution contained in the culture tank.

8. 8. The apparatus for producing photosynthetic microorganisms according to claim 6, wherein the nominal pore size of the micropores formed in the separation membrane is 5 μm or less.

9. 8. The apparatus for producing photosynthetic microorganisms according to claim 6 or 7, wherein the concentration of dissolved organic carbon in the permeate is 20 mg / L or less.

10. The apparatus for producing photosynthetic microorganisms according to claim 6 or 7, wherein the photosynthetic microorganisms are microalgae.

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