JP2014223024A - Culture method and culture apparatus of microalgae - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a culture method and a culture apparatus of marine microalgae which are capable of efficiently fixing carbon dioxide while suppressing metal corrosion of the culture apparatus.SOLUTION: A culture solution which consists of a culture medium whose salinity concentration is set to a lower concentration than a seawater salinity concentration and microalgae, is produced, carbon dioxide gas is fixed by supplying carbon dioxide gas to the culture solution, and culture of microalgae is performed. The total organic carbon content of the culture solution and a cell concentration of the culture solution are measured, a supply amount of the culture medium having a predetermined salinity concentration is controlled based on the measured total organic carbon content and cell concentration, and an increase rate of the total organic carbon content is maintained at a value near the maximum value. Since the microalgae can be continuously cultured under a condition where carbon dioxide can be efficiently fixed even in the state where the salinity concentration is set lower than the salinity concentration of seawater, carbon dioxide can be efficiently fixed while metal corrosion caused by salinity is suppressed.

Description

  The present invention relates to a method for culturing microalgae and a culture apparatus.

In recent years, in order to suppress global warming, reduction of the emission amount of carbon dioxide, which is one of the greenhouse gases, has been an issue.
As a means for reducing carbon dioxide, there is a method using photosynthesis of plants. Among plants, microalgae in particular are attracting attention as a promising means for reducing carbon dioxide because they have a high growth potential compared to terrestrial plants. For example, Patent Document 1 reports a microalgae that has a higher growth rate than conventional ones and can be cultured in large quantities.

  Here, algae is a general term for photosynthesis organisms excluding terrestrial plants (moss plants, fern plants, seed plants). Among them, small algae that cannot be seen without using a magnifying glass are It is called “microalgae”. So-called phytoplankton is an example of microalgae.

  A culture apparatus using photosynthesis of microalgae has been studied. For example, Patent Document 2 proposes a configuration of an apparatus that intermittently blocks sunlight to prevent light inhibition due to algae growth and increases the efficiency of algae photosynthesis. In addition, a process for synthesizing fuel while suppressing emissions of carbon dioxide at power plants and factories using microalgae that generates and accumulates oil components is also being studied.

  Microalgae used for carbon dioxide fixation include freshwater and marine ones. Some marine algae can be cultured even with a high concentration of carbon dioxide, such as chlorococcum litorale (see Non-Patent Document 1). High resistance to carbon dioxide not only enables direct introduction from a device that emits high concentration carbon dioxide, such as fuel cells, but also has the advantage of avoiding contamination of other microorganisms that cannot survive at that concentration .

JP 2000-050861 A Special Table 2000-504924

M. Ota et.al., Bioresource Technology 100 (2009), 5237-5242

  However, since marine microalgae literally live in seawater, the medium contains salt. Generally, seawater contains about 3.5% salinity. Salinity not only corrodes the metal of the culture system itself, but can also adversely affect other equipment around the culture system. Usually, metal parts with high corrosion resistance, such as titanium and SUS316L, are used in equipment that can be exposed to seawater. However, using corrosion-resistant metal parts for all peripheral equipment increases the cost. Not realistic.

  Then, an object of this invention is to provide the cultivation method and cultivation apparatus of marine microalgae which can fix a carbon dioxide efficiently, suppressing the metal corrosion of a cultivation apparatus.

  In order to solve the problems as described above, the method for culturing microalgae according to the present invention comprises a medium and a microalgae whose salinity is lower than seawater salinity and at least 5% of seawater salinity. A culture solution is generated, and carbon dioxide is supplied to the culture solution to culture microalgae.

  The salinity of the medium in the above-described method for culturing microalgae may be 50% or less of the seawater salinity.

  Measure the total organic carbon content and cell concentration of the culture solution in the above-mentioned microalgae cultivation method, and control the supply amount of the medium having a predetermined salinity based on the measured total organic carbon content and cell concentration. The increase rate may be maintained near the maximum value.

  The microalgae in the microalgae cultivation method may be chlorococcum litorale.

  The apparatus for culturing microalgae according to the present invention includes a culture vessel for storing a culture solution composed of a medium and microalgae whose salinity is lower than seawater salinity and at least 5% of seawater salinity, and culture. And means for supplying carbon dioxide gas to the liquid.

  The salinity of the medium in the microalgae culture apparatus may be 50% or less of the seawater salinity.

Means for measuring the total organic carbon content and cell concentration of the culture solution in the microalgae culture apparatus, and means for controlling the supply amount of the medium having a predetermined salinity based on the measured total organic carbon content and cell concentration And the increase rate of the total organic carbon amount may be maintained near the maximum value.

  The microalgae in the above-described microalgae culture apparatus may be chlorococcum litorale.

  According to the present invention, microalgae can be continuously cultured under conditions where carbon dioxide can be efficiently immobilized even in a state where the salinity concentration is set lower than the salinity concentration of seawater. It can fix carbon dioxide well.

  In addition, according to the present invention, since it is possible to continue culturing microalgae while maintaining the rate of increase of the total organic carbon content in the culture solution of microalgae in the vicinity of the maximum value, carbon dioxide while suppressing metal corrosion due to salt Can be fixed at a high rate.

FIG. 1 is a diagram showing an outline of a microalgae culture apparatus according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the salt concentration ratio of the culture solution of the present invention and the specific growth rate of microalgae. FIG. 3 is a graph obtained by measuring the time variation of the total organic carbon content of the culture solution using the salinity ratio of the culture solution in the present invention as a parameter. FIG. 4 is a graph obtained by converting the time change of the turbidity of the culture solution in the present invention into the time change of the cell concentration. FIG. 5 is a diagram illustrating a configuration example of the culture apparatus according to the embodiment of the present invention. FIG. 6 is a flowchart for explaining an example of the culture solution control method according to the embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Culture solution>
FIG. 1 is a drawing showing an outline of a microalgae culture apparatus according to an embodiment of the present invention. A solution of microalgae dispersed in a medium such as water is a culture solution of microalgae, which is stored in a culture vessel made of a transparent material. By irradiating the culture vessel with natural light or illumination light and supplying carbon dioxide to cause the microalgae to perform photosynthesis, the microalgae are cultured and carbon dioxide is immobilized.

  In this embodiment, chlorococcum litorale is used as the microalgae. Chlorococcum litorale is one of the marine microalgae that can be cultivated even with high concentration of carbon dioxide and produces lipids. As the culture medium, artificial seawater SP “DAIGO” and IMK culture medium “DAIGO” from Nippon Pharmaceutical Co., Ltd. were used. Artificial seawater SP “DAIGO” is artificial seawater containing 20747mg / L of sodium chloride and containing inorganic salts of seawater components. On the other hand, IMK medium “Digo” is a medium containing nutrient salts such as nitrogen and phosphorus. In general, these two types of media are mixed and cultured. In this example, the concentration of the salinity of the culture solution is reduced by reducing the concentration of the artificial seawater SP “Digo” to the normal concentration of the IMK medium Daigo. Was adjusted and cultured.

<Culture method>
A method for culturing microalgae according to an embodiment of the present invention will be described. In the present invention, the salinity of the culture medium and peripheral devices due to the salinity is suppressed by suppressing the salinity concentration of the medium containing the salinity as much as possible. In other words, the culture solution is produced by reducing the concentration of the artificial seawater SP “Daigo” when mixing the IMK medium “Daigo” with the artificial seawater SP “Daigo” so that the salinity is lower than the seawater salinity. Do. By adjusting the concentration of artificial seawater SP “Daigo”, a culture solution with a desired salinity ratio (ratio of salinity to seawater salinity), which is lower in salinity than seawater, is generated. It is possible to grasp the state of culture at each salinity ratio by culturing and measuring changes in the total organic carbon content and cell concentration over time. Here, the total amount of organic carbon can be directly measured by taking out a part of the culture solution, and the change in cell concentration can be measured by measuring the turbidity of the culture solution.

  FIG. 2 shows the results of measuring the specific growth rate by changing the salt concentration ratio of the culture solution. Here, the specific growth rate is the slope of the cell concentration in the logarithmic growth phase in the logarithmic growth phase in which the concentration of microalgae increases exponentially, and is one of the measures for measuring the state of growth. Even when the salt concentration ratio is lowered to about 30% to 50%, the decrease in the specific growth rate is about 15%. In addition, even when the salt concentration ratio is 16%, the specific growth rate decreases by about 20%, indicating that the culture is performed smoothly.

  Next, FIG. 3 shows the results of measuring the time variation of the total organic carbon content using the salinity ratio of the culture solution as a parameter. Here, the total amount of organic carbon is obtained by directly measuring organic carbon contained in a culture solution containing microalgae, and represents the total amount of carbon dioxide fixed by microalgae. Even when 190 hours have passed, the total organic carbon amount at a salt concentration ratio of 50% is only about 10% lower than that when the salt concentration ratio is 100%, and it can be confirmed that the culture is proceeding smoothly.

  In FIG. 3, the total amount of organic carbon after 190 hours when the salt concentration ratio is 5% is about half that when the salt concentration ratio is 100%. However, it can be seen that the total organic carbon amount increases smoothly between 100 hours and 200 hours, and the increase rate of the total organic carbon amount in this time zone shows a substantially maximum value in the entire time zone. Therefore, if the culture solution is adjusted so as to maintain the cell concentration in this time zone, that is, the medium is supplied, it is possible to perform continuous culture while maintaining the increase rate of the total organic carbon amount near the maximum value. .

  In FIG. 3, the increase rate of the total organic carbon amount in the time region where the elapsed time when the salinity ratio is 5% is 100 hours to 200 hours is 50 hours to 100 hours when the salinity concentration ratio is 100%. However, even if the salinity ratio is 5%, continuous culture can be performed by controlling the supply amount of the medium so as to maintain the cell concentration in the time range of 100 hours to 200 hours even when the salt concentration ratio is 5%. It can be seen that carbon dioxide can be immobilized.

  The cell concentration is measured by measuring the turbidity of the culture solution. FIG. 4 is a graph obtained by converting the time change of the turbidity of the culture solution performed in parallel with the measurement of the total amount of organic carbon into the time change of the cell concentration. The turbidity and cell concentration of the culture solution change with time as the culture progresses, and using this correlation between turbidity and cell concentration, the rate of increase in the total organic carbon content is maintained near the maximum value. Measure the turbidity range. For example, if the rate of increase in the total organic carbon content is to be maintained in the time domain value from 100 hours to 200 hours when the salinity ratio in FIG. The culture solution should be adjusted so that it is between. Similarly, the turbidity range in which the rate of increase in the total organic carbon amount is maintained near the maximum value can be determined at other salinity ratios. As described above, when the turbidity of the culture solution is used, it is possible to maintain the cell concentration at a desired value so that the increase rate of the total organic carbon amount maintains around the maximum value.

<Culture equipment>
Next, a configuration example of the culture apparatus according to the present embodiment will be described in detail with reference to FIG. The culture apparatus in this configuration example includes a light source 10 for photosynthesis, a medium 12 containing salt, a culture solution 11 composed of microalgae, a culture vessel 13 for holding it, a carbon dioxide supply device 20 for supplying carbon dioxide, a salt content Medium supply device 30 for supplying a medium containing a culture medium, a culture solution recovery device 40 for recovering a part of the culture solution, an organic carbon amount measurement device 50 for measuring the amount of organic carbon, and a turbidity measurement device for measuring the turbidity of the culture solution 60 and a culture fluid control device 70 for controlling the amount of culture medium supplied and the amount of culture fluid to be collected.

(1) Culture solution, culture vessel The culture solution 11 used in the present embodiment is composed of a medium 12 containing salt and microalgae, and is one of the marine microalgae as a microalgae and is cultured even in high-concentration carbon dioxide. A possible chlorococcum litorale was used. The salinity of the culture solution is set to be lower than the seawater salinity in order to suppress metal spoilage as much as possible, and is set to be at least 5% of the seawater salinity and stored in the culture vessel 13. Has been. Photosynthesis is performed using light from the light source 10 and carbon dioxide supplied from the carbon dioxide supply device to fix the carbon dioxide.

(2) Carbon dioxide supply device The carbon dioxide supply device 20 of the present configuration example includes a carbon dioxide supply source 21 and a valve 22 such as a fuel cell and a power generation facility. The carbon dioxide supply device 20 fixes carbon dioxide by supplying carbon dioxide to the culture solution. Chlorococcum litorale used this time can be cultivated even under high concentration of carbon dioxide, and it is also possible to supply carbon dioxide directly from devices that discharge high concentration carbon dioxide such as fuel cells and thermal power plants.

(3) Medium supply apparatus The medium supply apparatus 30 of this configuration example includes a medium 12 having a predetermined salt concentration, a medium container 31 that stores the medium, and a pump 32 that draws the medium from the medium container and supplies the medium to the culture container 13. The flow rate of the pump 32 is configured to be controllable by a control signal 71 from a computer (culture medium control device 70). By controlling the flow rate of the pump 32, the cell concentration of the culture solution 11 in the culture vessel 13 can be controlled to a desired value. It is also possible to set the salt concentration of the culture solution 11 in the culture container 13 so as to maintain the initially set salt concentration by adjusting the salt concentration of the medium 12 in the medium container 31. It is also possible to change to a desired value.

(4) Culture medium recovery device When continuous culture is performed, the culture medium is supplied to maintain the concentration of microalgae at a predetermined value, and thus the culture medium is recovered as necessary. The culture solution recovery apparatus 40 of this configuration example includes a culture solution container 41 that stores the culture solution and a pump 42 that pumps the culture solution from the culture vessel. As with the medium supply device, the flow rate of the pump can be controlled by a control signal 71 from a computer (culture liquid control device 70). Moreover, in order to directly measure the amount of organic carbon, it also has a function of supplying a part of the collected culture solution to the organic carbon amount measuring apparatus 50 described later.

(5) Organic carbon content measuring device The organic carbon content measuring device 50 measures the time change of the total organic carbon content of the culture solution in order to grasp the change in the increase rate of the total organic carbon content. The total amount of organic carbon can be directly measured using a part of the culture solution obtained by the culture solution recovery apparatus 40. The measured total organic carbon amount information 51 is sent to a culture solution control device 70 to be described later, and becomes basic data for controlling the increase rate of the total organic carbon amount to be near the maximum value.

(6) Turbidity measuring device The turbidity measuring device 60 measures the turbidity of the culture solution 11 in parallel with the measurement of the time variation of the total organic carbon content. The turbidity of the incubator can be measured by measuring the absorbance at a fixed wavelength using a part of the culture solution obtained by the culture solution recovery apparatus 40. By measuring the time variation of the total organic carbon amount and the turbidity of the culture solution in parallel, it is possible to grasp the turbidity range in which the increase rate of the total organic carbon amount is near the maximum value. The measured culture fluid turbidity data 61 is sent to a culture fluid control device 70 to be described later, and serves as basic data for specifying the turbidity at which the increase rate of the total organic carbon amount is near the maximum value.

(7) Culture Solution Control Device The culture solution control device 70 has an increase rate of the total organic carbon amount based on the total organic carbon amount 51 of the culture solution and the turbidity data 61 of the culture solution measured by the organic carbon amount measuring device 50. The supply amount of the culture medium and the recovery amount of the culture solution are controlled so as to maintain the vicinity of the maximum value.

<Control of culture solution>
Hereinafter, a method for controlling the culture solution including the operation of the culture solution control apparatus 70 will be described. FIG. 6 is a flowchart for explaining the culture solution control method of the present invention.
First, a culture solution is generated so that the salinity concentration is lower than the seawater salinity concentration by lowering the mixing ratio of the artificial seawater SP “DAIGO” when mixing the culture medium to a predetermined salinity concentration (S1), The culture solution is stored in the culture vessel 13 (S2). Carbon dioxide is supplied thereto by the carbon dioxide supply device 20, and the fixation of carbon dioxide is started (S3).

  When the fixation of carbon dioxide progresses and the culture progresses smoothly, the cell concentration of microalgae increases, but the growth rate decreases over time. As described above, the turbidity range of the culture solution in which the change over time of the total organic carbon amount at the predetermined salinity concentration of the culture apparatus and the rate of increase thereof is near the maximum value is measured in advance, and the turbidity is within the range. Adjust the culture to maintain.

  First, the time variation of the total organic carbon amount at a predetermined salinity concentration of the culture apparatus used as shown in FIG. Measure turbidity data (S4). The total organic carbon content information 51 and the turbidity data 61 are provided to the culture solution controller 70. From the obtained turbidity data 61, the culture solution control device 70 determines a turbidity range in which the increase rate of the total organic carbon amount is near the maximum value, and stores the data (S5). For example, when the salinity concentration ratio is 5%, the turbidity is in the time range of 100 hours to 200 hours.

  Next, continuous culture is performed while supplying the culture medium and collecting the culture solution (S6). In continuous culture, only the turbidity of the culture solution is measured, and turbidity data 61 is provided to the culture solution control device 70 (S7). The culture solution control device 70 determines whether the turbidity of the culture solution is within the turbidity range determined above (S8), and controls the medium supply device 30 and the culture solution collection device 40 so as not to depart from the range. 71 is sent to control the supply amount of the medium and the recovery amount of the culture solution (S9).

  As shown in FIG. 3, the time change of the rate of increase in the total organic carbon amount varies depending on the salinity of the culture solution, so that the measured turbidity value does not deviate from the predetermined range based on the data measured in advance. In addition, if control is performed so that a medium having a desired salinity concentration is supplied, continuous culture can be performed while suppressing the metal corrosion while maintaining the salinity concentration at a desired value.

  In addition, as described above, in continuous culture, control is performed by measuring only the turbidity of the culture solution. If necessary, the total organic carbon content is measured by the total organic carbon content measuring device 50, and the total organic carbon content is measured. You may make it confirm whether it is controlled so that an increase rate may become the maximum value vicinity.

  As described above, according to the embodiment of the present invention, carbon dioxide can be efficiently immobilized even when the salinity concentration is set lower than the salinity concentration of seawater, for example, when it is set to 50% or less of the seawater salinity concentration. Since microalgae can be cultured under conditions, carbon dioxide can be efficiently immobilized while suppressing metal corrosion due to salt.

  Further, according to the embodiment of the present invention, it is possible to continue culturing microalgae while maintaining the increase rate of the total organic carbon content in the culture solution of microalgae near the maximum value. Even when the seawater salt concentration is set to 5%, carbon dioxide can be immobilized at a high rate while suppressing metal corrosion due to salt.

  In the embodiment of the invention described above, the culture is performed while keeping the salinity concentration of the culture solution constant. However, the salinity concentration may be changed within a range in which metal corrosion due to the salinity can be suppressed. . That is, the salinity concentration of the culture medium supplied by the medium supply means may be adjusted to a desired salinity concentration to change the salinity concentration of the culture solution from the initial salinity concentration to the desired salinity concentration.

  The present invention can be applied to a system for culturing marine microalgae, a system for absorbing high-concentration carbon dioxide such as a thermal power plant, and the like.

  DESCRIPTION OF SYMBOLS 10 ... Light source, 11 ... Culture solution, 12 ... Medium, 13 ... Culture container, 20 ... Carbon dioxide supply apparatus, 21 ... Carbon dioxide supply source, 22 ... Valve, 30 ... Medium supply apparatus, 31 ... Medium container, 32 ... Pump DESCRIPTION OF SYMBOLS 40 ... Culture solution collection device, 41 ... Culture solution container, 42 ... Pump, 50 ... Organic carbon content measurement device, 51 ... Organic carbon content information, 60 ... Turbidity measurement device, 61 ... Turbidity data, 70 ... Culture solution Control device, 71... Control signal.

Claims (8)

  A culture solution composed of a medium and a microalgae having a salinity concentration lower than the seawater salt concentration and set to at least 5% of the seawater salt concentration is generated, and carbon dioxide is supplied to the culture solution to culture the microalgae. A method for culturing microalgae.   The method for culturing microalgae according to claim 1, wherein the salinity of the medium is 50% or less of the seawater salinity.   Measure the total organic carbon content and cell concentration of the culture solution, control the supply amount of the medium having a predetermined salinity based on the measured total organic carbon content and cell concentration, and maximize the increase rate of the total organic carbon content The method for culturing microalgae according to claim 1 or 2, wherein the microalgae is maintained in the vicinity of the value.   The method for culturing microalgae according to any one of claims 1 to 3, wherein the microalgae is chlorococcum litorale.   A culture vessel for storing a culture solution composed of a medium and microalgae whose salinity is lower than seawater salinity and at least 5% of the seawater salinity, and means for supplying carbon dioxide to the culture Microalgae culture device.   The apparatus for culturing microalgae according to claim 5, wherein the salinity of the medium is 50% or less of the seawater salinity.   Means for measuring the total organic carbon amount and cell concentration of the culture solution, and means for controlling the supply amount of a medium having a predetermined salinity based on the measured total organic carbon amount and cell concentration, The apparatus for culturing microalgae according to claim 5 or 6, wherein the rate of increase in carbon content is maintained in the vicinity of a maximum value.   The apparatus for culturing microalgae according to any one of claims 5 to 7, wherein the microalgae is chlorococcum litorale.

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