Alga culture device and gas supply method

Abstract

An alga culture device (100) is provided with: a culture tank (1) in which an alga is cultured; an alga concentration sensor (6) for measuring the concentration of the alga; a dissolved gas sensor (5) for measuring the concentration of a dissolved gas in the culture tank (1); a gas supply amount adjustment unit (3) for supplying an adjusted amount of a specific gas to the culture tank (1); a dissolved gas target concentration calculation unit (8) for calculating a target value for the concentration of the dissolved gas on the basis of a measurement value obtained by the alga concentration sensor (6); and a target gas supply amount calculation unit (9) for calculating a target gas supply amount from the target value calculated by the dissolved gas target concentration calculation unit (8) and a measurement value obtained by the dissolved gas sensor (5), and then supplying the calculated target gas supply amount to the gas supply amount adjustment unit (3). The alga culture device (100) is configured such that the specific gas is suppled from the gas supply amount adjustment unit (3) to the culture tank (1) on the basis of the target gas supply amount.

Description

Algae cultivation device and gas supply method

[0001] The present disclosure relates to an algae cultivation apparatus and a gas supply method.

[0002] Recently, attention has been focused on the technology of cultivating algae that can be converted into biofuels and contribute to decarbonization. Conventionally, algae cultivation required supplying carbon dioxide or oxygen gas to a culture solution and dissolving the gas. To efficiently cultivate algae, the amount of gas supplied must be appropriately controlled. Therefore, the dissolved gas concentration was measured, and the amount of gas supplied to the culture solution was controlled according to the measured value (see, for example, Patent Document 1).

[0003] Here, algae are defined as organisms that perform oxygenic photosynthesis, excluding mosses, ferns, and seed plants, which primarily grow on land. Among these, algae that can be seen with the naked eye, such as wakame seaweed, kombu seaweed, and mozuku seaweed, are sometimes referred to as "macroalgae," while algae that are too small to be distinguished by the naked eye are sometimes referred to as "microalgae." Furthermore, labyrinthulae, heterotrophic eukaryotic microorganisms that do not perform photosynthesis, are sometimes treated as algae because they are closely related to algae.

[0004] In addition, conventionally, the gas supply required for microalgae cultivation was inappropriate, leaving room for improvement in cultivation efficiency. Specifically, the longer the cultivation period for microalgae, the greater the number of microalgae or the amount of organic matter, such as oils and fats, accumulated within the cells, which increases the microalgae concentration in the culture solution. However, as the concentration increases, the dissolved gas concentration required for efficient cultivation also changes. Furthermore, the dissolved gas concentration required for efficient cultivation varies depending on the substrate concentration in the culture solution required for microalgae growth or the water temperature. However, conventionally, the dissolved gas concentration has been controlled independently of the microalgae concentration, substrate concentration, or water temperature (see, for example, Patent Document 2).

[0005] JP 2012-23978 A JP 2019-110767 A

[0006] The longer the culture period for the above-mentioned microalgae, the greater the number of microalgae and the amount of accumulated organic matter, such as fats and oils, within the cells. This increases the concentration of microalgae in the culture solution, but as the concentration increases, the dissolved gas concentration required for efficient culture also changes. However, in conventional techniques, the dissolved gas concentration is controlled independently of the microalgae concentration, which can result in low culture efficiency. Specifically, this can lead to problems such as slow culture speed and inefficient gas supply.

[0007] The present disclosure discloses technology for solving the above-mentioned problems, and aims to provide an algae culture device that can culture algae at a dissolved gas concentration with high culture efficiency by controlling the target dissolved gas concentration in the culture tank where algae are cultured based on the algae concentration, or substrate concentration, or water temperature.

[0008] The algae culture device of the present disclosure comprises: a culture tank for culturing algae; an algae concentration sensor for measuring the concentration of the algae; a dissolved gas sensor for measuring the concentration of dissolved gas in the culture tank; a gas supply amount adjustment unit for supplying an adjusted amount of a predetermined gas to the culture tank; a target dissolved gas concentration calculation unit for calculating a target value for the concentration of the dissolved gas based on the measurement value of the algae concentration sensor; and a target gas supply amount calculation unit for calculating a target gas supply amount from the target value calculated by the target dissolved gas concentration calculation unit and the measurement value of the dissolved gas sensor, and supplying the calculated target gas supply amount to the gas supply amount adjustment unit, and is characterized in that the predetermined gas is supplied to the culture tank from the gas supply amount adjustment unit based on the target gas supply amount.

[0009] According to the algae cultivation device disclosed herein, by controlling the target dissolved gas concentration in the cultivation tank in which algae are cultivated based on the algae concentration, or the substrate concentration, or the water temperature, it is possible to provide a device that can cultivate algae at a dissolved gas concentration that results in high cultivation efficiency.

[0010] FIG. 1 is a block diagram showing one configuration of an algae culture apparatus according to embodiment 1. FIG. 2 is a diagram for explaining the relationship between culture time, algae concentration, and amount of accumulated oil and fat in the algae culture apparatus. FIG. 3 is a block diagram showing one configuration of an algae culture apparatus according to embodiment 2. FIG. 4 is a block diagram showing one configuration of an algae culture apparatus according to embodiment 3. FIG. 5 is a block diagram showing one configuration of an algae culture apparatus according to embodiment 4. FIG. 6 is a block diagram showing one configuration of an algae culture apparatus according to embodiment 5. FIG. 7 is a diagram for explaining an example of a database update unit of an algae culture apparatus according to embodiment 6. FIG. 8 is a diagram for explaining the algae growth rate relative to the gas supply amount and the dissolved gas concentration. FIG. 9 is a diagram for explaining the cost of supplying a unit amount of gas relative to the gas supply amount and the dissolved gas concentration. FIG. 10 is a diagram for explaining hardware used in the algae culture apparatus according to embodiments 1 to 6.

[0011] The "algae culture apparatus" covered by this disclosure will be referred to as a "microalgae culture apparatus" when it is necessary to distinguish it from other algae culture apparatuses. Here, as mentioned above, microalgae refers to algae of a size that is difficult to distinguish with the naked eye. In this disclosure, the algae culture apparatus, which is an apparatus for efficiently cultivating the above-mentioned algae, will be described below with reference to the drawings.

[0012] First Embodiment An example of an algae culture apparatus according to a first embodiment will be described first with reference to Figures 1 and 2. Generally, a culture tank (with a volume ranging from several liters to several thousand m 3 In the case of microbial bioreactors, the longer the culture period, the greater the number of microalgae and the amount of accumulated organic matter, such as fats and oils, inside the cells (collectively referred to as organic matter accumulation), which causes changes in the concentration of dissolved gases, such as CO2. Therefore, sensors are needed to detect these changes. Furthermore, because the dissolved gas concentration changes, it is necessary to adjust the amount of gas supplied to the culture tank.

[0013] FIG. 1 is a block diagram showing an example of the configuration of an algae culture device 100 according to the first embodiment, including the components described above. In FIG. 1 , a culture tank 1 for culturing algae contains a culture solution 11. To efficiently cultivate algae in the culture solution 11, the dissolved gas concentration in the culture solution needs to be adjusted and maintained at an appropriate level in response to changes in the culture conditions (specifically, changes in the algae concentration, for example). Therefore, in response to changes in the culture conditions, a gas containing a predetermined gas is supplied from a gas supply unit 2 in an amount adjusted by a gas supply amount adjuster 3 via a gas dissolver 4, which dissolves the dissolved gas in the culture solution.

[0014] Here, in order to efficiently cultivate algae, it is necessary to appropriately change the dissolved gas concentration in the culture solution each time in accordance with changes in the culture conditions and maintain it at an appropriate level. The reason for this will be explained below using Figure 2.

[0015] In Figure 2, the horizontal axis represents the culture time, and the vertical axis represents the algae concentration and the amount of accumulated oil (hereinafter also referred to as the amount of accumulated oil), with both amounts being shown on an arbitrary scale. In the figure, the solid line curve represents the general change in algae concentration over time, and the dotted line curve represents the general change in the amount of accumulated oil over time. Specific numerical values ​​are: the ratio of the algae concentration at the start of culture to the end of culture is 1:10 to 10,000; the ratio of the amount of accumulated oil at the start of culture to the end of culture is similarly 1:10 to 1,000,000; and the ratio of the required gas supply amount at the start of culture to the end of culture is 1:2 to 1,000. The unit of the gas supply amount required per liter of culture solution is usually expressed in liters per minute (liters / min).

[0016] As can be seen from Figure 2, the curve showing the change in algae concentration over time includes a logarithmic growth period ta, during which the algae concentration increases logarithmically, and a linear period tb (whereas the change in the amount of accumulated oil over time is a period during which the amount of accumulated oil increases gradually). The curve showing the change in algae concentration over time also includes a period during which the change in algae concentration is almost constant (whereas the curve showing the change in the amount of accumulated oil over time includes a period during which the amount of accumulated oil increases rapidly), i.e., a period called a stationary period tc.

[0017] 2 also shows that there is a difference in culture time between the logarithmic growth phase ta and the linear phase tb and the stationary phase tc (the stationary phase tc appears after the logarithmic growth phase ta and the linear phase tb). Therefore, it is presumed that the optimal dissolved gas concentrations differ between the logarithmic growth phase and the stationary phase. The stationary phase can also be considered a period in which the number of algae does not increase significantly, but the algae themselves grow, i.e., the weight per individual or the amount of oil and fat accumulated within each individual increases.

[0018] As explained above, there is a time lag between the period when algae concentration increases rapidly and the period when the amount of accumulated oil in the algae increases rapidly, and it can be seen that the period when the amount of accumulated oil in the algae (hereinafter, the amount of accumulated oil is also referred to as the amount of accumulated organic matter, which is a broader concept that includes oil) increases rapidly follows the period when algae concentration increases rapidly. This indicates that the increase in the number of algae (which can also be said to be the number of algae cells), which corresponds to the increase in algae concentration, comes first, and then, after the increase in the number of algae reaches saturation, oil accumulates inside each algae.

[0019] Therefore, it is presumed that the amount of gas dissolved in the culture solution (dissolved gas concentration) needs to be adjusted according to the growth state of the algae. In the above, the amount of accumulated oil refers to the amount of oil inside (accumulated in) the algae per dry weight of the algae, and is defined as the amount of oil (mg) / weight of the algae (g).

[0020] Therefore, the algae culture device disclosed herein is provided with an algae concentration sensor 6 and a dissolved gas sensor 5, and is configured as a device that includes a target dissolved gas concentration calculation unit and a target gas supply calculation unit, as described below, to adjust the amount of gas supplied to the culture tank based on the measurement results of these sensors.

[0021] 1 , the amount of gas to be dissolved in the culture solution is adjusted by sending the result of calculation of the target gas supply amount by the target gas supply amount calculation unit 9 to the gas supply amount adjustment unit 3 based on the dissolved gas concentration in the culture solution measured by the dissolved gas sensor 5 and the target dissolved gas concentration calculated by the target dissolved gas concentration calculation unit 8 based on the algae concentration in the culture solution measured by the algae concentration sensor 6. The target dissolved gas concentration calculation unit 8 also calculates values ​​such as the algae growth rate per unit gas supply amount (described in detail later) by feeding back the output from the gas supply amount adjustment unit 3. Here, examples of measurement methods using the algae concentration sensor include a method of calculating the algae concentration in the culture solution by measuring transmitted light at a wavelength of 660 nm, and a method of calculating the algae concentration by optically measuring chlorophyll contained in the algae.

[0022] Here, to grow algae, nutrients such as organic matter, nitrogen, and phosphorus, which are called substrates and serve as nutrients for algae, are required, and these substrates are supplied in the required amounts from the substrate supply unit 10. Typical examples of substrates include organic carbon, ammonia, and phosphorus. These components are also typical nutrients essential for the growth of microalgae.

[0023] The algae culture device of the first embodiment is configured as described above, and adjusts the amount of gas dissolved in the algae culture solution based on the measurement results of the algae concentration sensor in the culture solution, thereby improving the efficiency of algae culture. Here, the term "culture efficiency" refers to the value obtained by dividing the amount of organic matter (such as oils and fats) obtained from microalgae after a certain period of culture by the running cost of the culture, or its reciprocal.

[0024] In addition, in conventional algae culture devices, the dissolved gas concentration is controlled independently of the microalgae concentration, which results in low culture efficiency, i.e., there is a risk of slow culture speed and inefficient gas supply.

[0025] In the above, the "predetermined gas" refers to carbon dioxide (CO2) or oxygen (O2). In this case, the (type of) predetermined gas varies depending on the algae being cultivated. For example, algae that grow by photosynthesis require carbon dioxide (however, carbon dioxide diluted with air is acceptable, rather than 100% CO2), and algae that grow on organic matter require oxygen (however, air is generally supplied).

[0026] Incidentally, when culturing algae, it is estimated that the concentration of dissolved gases changes depending on the concentration of the substrate in the culture solution or the water temperature of the culture solution. Therefore, in some cases, it is expected that a more efficient algae culture device can be developed by providing a water quality sensor that measures the concentration of the substrate or the water temperature and feeding back the measurement results from this water quality sensor to set the target dissolved gas concentration.

[0027] Second Embodiment Next, an algae culture apparatus 101 according to a second embodiment will be described with reference to Figure 3. In the algae culture apparatus according to the second embodiment, a water quality sensor is provided instead of the algae concentration sensor constituting the algae culture apparatus according to the first embodiment.

[0028] Figure 3 is a block diagram showing the configuration of an algae culture device in which a water quality sensor 7 is used instead of the algae concentration sensor 6 of embodiment 1 as sensor information to be fed back to the target dissolved gas concentration calculation unit 8.

[0029] This water quality sensor 7 is a sensor for measuring the water temperature of the culture solution 11, which affects the concentration of algae cultured in the culture tank 1, and the concentrations of organic carbon, ammonia, and phosphorus, which are substrates in the culture solution 11. During measurement, this water quality sensor measures one or more of the organic carbon concentration, ammonia concentration, phosphorus concentration, and water temperature, and outputs the measurement results to the target dissolved gas concentration calculation unit 8. Note that the other configurations are the same as those of the algae culture apparatus of embodiment 1, so a description thereof will be omitted here.

[0030] In the above-mentioned water quality sensor measurements, the organic carbon concentration, ammonia concentration, and phosphorus concentration must each be measured using separate sensors. Specifically, methods for measuring organic carbon concentration include, for example, calculating the organic carbon concentration by measuring the amount of carbon dioxide in the gas obtained by burning sample water, or calculating the organic carbon concentration from the absorbance at a specific wavelength. Methods for measuring ammonia concentration include, for example, measuring the ammonia nitrogen concentration using an ion electrode, or measuring the ammonium ion concentration by ion chromatography. Methods for measuring phosphorus concentration include, for example, calculating the total phosphorus concentration in sample water using molybdenum blue absorptiometry, or measuring the phosphate concentration by ion chromatography. These concentrations can be measured continuously using a water quality sensor installed on-site, or periodically sampling the culture solution and measuring it off-site using a water quality sensor. The measurement results are input into the target dissolved gas concentration calculation unit.

[0031] As the algae culture apparatus of embodiment 2 is configured as described above, it is possible to suppress the influence of the water temperature of the culture solution 11, which affects the algae concentration, and to suppress the influence of changes in the concentrations of organic carbon, ammonia, and phosphorus, which are substrates in the culture solution 11, thereby increasing the algae growth efficiency.

[0032] Third Embodiment Next, an algae culture apparatus 102 according to a third embodiment will be described with reference to Figure 4. Figure 4 is a block diagram showing the configuration of the algae culture apparatus according to the third embodiment. As shown in Figure 4, the algae culture apparatus according to the third embodiment differs from the algae culture apparatus according to the first and second embodiments in that it is provided with both an algae concentration sensor and a water quality sensor as components for grasping the status of the culture solution. The results measured by these sensors are output to the target dissolved gas concentration calculation unit 8. Note that the other configurations are the same as those of the algae culture apparatus according to the first or second embodiment, and therefore will not be described here.

[0033] Since the algae culture device of embodiment 3 is configured as described above, the amount of gas dissolved in the algae culture solution can be adjusted not only by reflecting the measurement results of the algae concentration sensor in the culture solution, but also by reflecting the measurement results of the water quality sensor, making it possible to culture algae in a culture solution that is more suitable for algae growth and further improving the algae culture efficiency. Note that when setting the gas supply amount, the values ​​of the setting parameters algae concentration, substrate concentration, and water temperature do not have the same influence on determining the culture efficiency, but rather vary depending on conditions such as the type of algae being cultured and the culture cost.

[0034] Fourth Embodiment Next, an algae culture apparatus 103 according to a fourth embodiment will be described with reference to Figure 5. Figure 5 is a block diagram showing the configuration of the algae culture apparatus according to the fourth embodiment. In the algae culture apparatus according to the fourth embodiment, in addition to the components of the algae culture apparatus according to the third embodiment, the database 12 shown in Figure 5 stores data on measurement results such as concentrations measured by the algae concentration sensor and the water quality sensor, and data on the target dissolved gas concentration calculated by the target dissolved gas concentration calculation unit, as well as data showing the correlation between these three pieces of data.

[0035] Here, the correlation is such that when the algae concentration and water quality are set to certain values, the target dissolved gas concentration (value) to be set is set and stored. Data relating to this correlation is then transferred to and from the target dissolved gas concentration calculation unit 8.

[0036] Since the algae culture apparatus of embodiment 4 is configured as described above, the target dissolved gas concentration calculation unit 8 can not only calculate the target dissolved gas concentration based on the measurement results of the algae concentration sensor and the water quality sensor, but also stores correlation data between the measurement result data, such as concentrations measured by the algae concentration sensor and the water quality sensor, and the target dissolved gas concentration data calculated by the target dissolved gas concentration calculation unit.Therefore, even if the target dissolved gas concentration calculation unit is no longer able to calculate the target dissolved gas concentration, the target dissolved gas concentration can be determined from the measurement results measured by the algae concentration sensor and the water quality sensor using the correlation data stored in database 12, and this determined value can be used in the target gas supply amount calculation unit 9.

[0037] Fifth Embodiment Next, an algae culture apparatus 104 according to a fifth embodiment will be described with reference to Fig. 6. Fig. 6 is a block diagram showing the configuration of an algae culture apparatus according to the fifth embodiment. In addition to the components of the algae culture apparatus according to the fourth embodiment, the algae culture apparatus according to the fifth embodiment includes a database update unit 13 that updates the correlations stored in the database 12, as shown in Fig. 6.

[0038] The database update unit 13 can update the above-mentioned correlations stored in the database 12 based on plant data including the culture time in the culture tank, the relationship between the culture time and the gas supply amount, the algae concentration measured by the algae concentration sensor, the measurement values ​​measured by the water quality sensor, and the dissolved gas concentration measured by the dissolved gas sensor, as well as the relationship between the culture time and the amount of organic matter accumulated in the algae stored in the database, and the gas cost per unit gas supply amount. Typical timings for updating include after a certain period of time has passed, when the culture is completed, or after an analysis of the amount of accumulated oil and fat.

[0039] In addition, in the algae culture device 104 according to embodiment 5, the database 12 stores the relationship between a given culture time and the amount of organic matter accumulated in the algae, the relationship between a pre-determined culture time and the algae growth rate per unit gas supply, and the cost of gas per unit gas supply.

[0040] Since the algae culture apparatus according to the fifth embodiment is configured as described above, it is possible to reflect the plant data described above and efficiently grow algae. Here, since it is possible to reflect data on the algae growth rate per unit gas supply amount, the algae culture apparatus according to the fifth embodiment can reduce the cost of culturing algae.

[0041] Sixth Embodiment Next, an algae culture apparatus according to a sixth embodiment will be described below with reference to Figures 7, 8A, and 8B.

[0042] 7 is a diagram showing a learning device 14 using a machine learning function applied to the database update unit 13, which is a component of the algae culture apparatus according to embodiment 6. In the algae culture apparatus according to embodiment 6, the correlations, which are data in the database 12, are updated based on the results obtained by this learning device 14. Other than this learning device 14, the algae culture apparatus according to embodiment 6 is the same as that according to embodiment 5.

[0043] Next, details of the learning device 14 shown in Figure 7 will be described. The learning device 14 shown in Figure 7 is composed of a data acquisition unit 15 and a model generation unit 16. The learning device 14 exchanges data and trained models with the database 12, collecting a large amount of data, such as plant data, obtained from various sensors and stored in the database 12 in the data acquisition unit 15. Based on the large amount of data acquired by the data acquisition unit, the model generation unit 16 uses machine learning to generate a model that learns the relationship between the algae growth rate, gas supply amount, and dissolved gas concentration in the algae culture apparatus. This makes it possible to reduce the cost of culturing algae in the algae culture apparatus. This will be described in more detail below using Figures 8A and 8B.

[0044] FIG. 8A is a graph showing the relationship between the gas supply amount, dissolved gas concentration (horizontal axis of the graph), and algae growth rate (vertical axis of the graph), with the curves in the graph illustrating the characteristics. Meanwhile, FIG. 8B is a graph showing the relationship between the gas supply amount, dissolved gas concentration (horizontal axis of the graph), and the cost of supplying a unit amount of gas (vertical axis of the graph), with the curves in the graph illustrating the characteristics. Here, the cost of supplying a unit amount of gas includes the price of the gas and the cost associated with the blower that supplies the air. From FIG. 8A , the algae growth rate reaches its maximum value when the gas supply amount is vc and the dissolved gas concentration is nc. From FIG. 8B , the cost of supplying a unit amount of gas reaches its maximum value when the gas supply amount is vb and the dissolved gas concentration is nb.

[0045] From the above, it can be seen that the gas supply amount or dissolved gas concentration at which the algae growth rate reaches its maximum is different from the gas supply amount or dissolved gas concentration at which the cost per unit amount of gas reaches its maximum. From the viewpoint of cost, the cost per unit amount of gas is more important. Therefore, when determining the gas supply amount or dissolved gas concentration for an algae culture device from the viewpoint of cost-effectiveness, it is necessary to place more emphasis on the characteristics of the curve shown in Figure 8B.

[0046] Furthermore, considering the ultimate goal of this development, which is the cultivation of microalgae that can be converted into biofuels, the amount of fat accumulated in the algae is more important than the algae concentration in the culture tank. Therefore, as explained in Figure 2 above, it is important to develop a culture plan that places greater emphasis on the change in the amount of fat accumulated over the culture time. Specifically, it is necessary to adjust the amount of gas supplied to the culture solution (dissolved gas concentration) according to the growth state of the algae.

[0047] In the above description of the algae culture apparatus of Embodiments 1 to 6, the culture tank is designed to be completely mixed, and the distribution of algae within the culture tank is not taken into consideration. Therefore, if the culture tank is not completely mixed and there is a bias in the dissolved gas concentration, algae concentration, water quality, etc. within the tank, mixing must be performed using a paddle, stirring tank, pump, or the like. For example, it may be better to consider the distribution (difference) of dissolved gas concentration between the peripheral region and the central region of the culture tank, and in such cases, mixing is necessary.

[0048] The algae culture device 100 is configured with a processor 200 and a storage device 201, as shown in FIG. 9 , which illustrates an example of its hardware. The storage device 201 includes a volatile storage device such as a random access memory (not shown), and a non-volatile auxiliary storage device such as a flash memory. A hard disk auxiliary storage device may be included instead of the flash memory. The processor 200 executes a program input from the storage device 201. In this case, the program is input to the processor 200 from the auxiliary storage device via the volatile storage device. The processor 200 may output data such as calculation results to the volatile storage device of the storage device 201, or may store the data in the auxiliary storage device via the volatile storage device.

[0049] Although various exemplary embodiments and examples are described in this disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are anticipated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0050] REFERENCE SIGNS LIST 1 Cultivation tank, 2 Gas supply unit, 3 Gas supply amount adjustment unit, 4 Gas dissolution unit, 5 Dissolved gas sensor, 6 Algae concentration sensor, 7 Water quality sensor, 8 Target dissolved gas concentration calculation unit, 9 Target gas supply amount calculation unit, 10 Substrate supply unit, 11 Culture solution, 12 Database, 13 Database update unit, 14 Learning device, 15 Data acquisition unit, 16 Model generation unit, 100, 101, 102, 103, 104 Algae cultivation device, 200 Processor, 201 Storage device

Claims

1. An algae culture device comprising: a culture tank for culturing algae; an algae concentration sensor for measuring the concentration of the algae; a dissolved gas sensor for measuring the concentration of dissolved gas in the culture tank; a gas supply amount adjustment unit for supplying a predetermined gas of an adjusted amount to the culture tank; a target dissolved gas concentration calculation unit for calculating a target value for the concentration of the dissolved gas based on a measurement value of the algae concentration sensor; and a target gas supply amount calculation unit for calculating a target gas supply amount from the target value calculated by the target dissolved gas concentration calculation unit and the measurement value of the dissolved gas sensor and supplying the calculated target gas supply amount to the gas supply amount adjustment unit, wherein the predetermined gas is supplied from the gas supply amount adjustment unit to the culture tank based on the target gas supply amount.

2. An algae culture device comprising: a culture tank for culturing algae; a water quality sensor for measuring any one of the water temperature, organic carbon concentration, ammonia concentration, and phosphorus concentration in the culture tank; a dissolved gas sensor for measuring the concentration of dissolved gas in the culture tank; a gas supply amount adjustment unit for supplying a predetermined gas of an adjusted amount to the culture tank; a target dissolved gas concentration calculation unit for calculating a target value for the concentration of the dissolved gas based on the measurement value of the water quality sensor; and a target gas supply amount calculation unit for calculating a target gas supply amount from the target value calculated by the target dissolved gas concentration calculation unit and the measurement value of the dissolved gas sensor and supplying the calculated target gas supply amount to the gas supply amount adjustment unit, wherein the predetermined gas is supplied from the gas supply amount adjustment unit to the culture tank based on the target gas supply amount.

3. An algae culture device as described in claim 1 or 2, characterized in that it has an algae concentration sensor that measures the concentration of the algae, and a water quality sensor that measures one of the water temperature, organic carbon concentration, ammonia concentration, and phosphorus concentration in the culture tank, and the target dissolved gas concentration calculation unit calculates a target value for the concentration of the dissolved gas based on the measurement values ​​of the algae concentration sensor and the water quality sensor.

4. The algae culture device described in claim 3, characterized in that it has a database that stores the correlation between the measurement values ​​measured by the algae concentration sensor and the water quality sensor and the target value of the dissolved gas concentration, and the target dissolved gas concentration calculation unit calculates the target value of the dissolved gas concentration from the correlation stored in the database based on the measurement values ​​of the algae concentration sensor and the water quality sensor.

5. The algae culture device described in claim 4, characterized in that the database stores the relationship between a given culture time and the amount of organic matter accumulated in the algae, the relationship between a predetermined culture time and the algae growth rate per unit amount of gas supplied, and the cost of gas supply per unit amount of gas supplied, and the device has a database update unit that updates the correlations stored in the database based on plant data including the culture time in the culture tank, the relationship between the culture time and the gas supply amount, the algae concentration measured by the algae concentration sensor, the measurement values ​​measured by the water quality sensor, and the dissolved gas concentration measured by the dissolved gas sensor, and the relationship between the culture time and the amount of organic matter accumulated in the algae stored in the database, and the gas cost per unit amount of gas supplied.

6. The algae culture apparatus according to claim 5, characterized in that the database update unit has a database in which the correlations are updated by machine learning.

7. An algae culture apparatus as described in claim 1 or 2, characterized in that the algae is microalgae and the specified gas is carbon dioxide or oxygen.

8. A gas supply method using an algae culture apparatus having an algae-containing culture tank, an algae concentration sensor for measuring the concentration of the algae, a dissolved gas sensor for measuring the concentration of dissolved gas in the culture tank, and a gas supply amount adjustment unit for supplying an adjusted amount of a predetermined gas to the culture tank, characterized in that a target value for the concentration of the dissolved gas is calculated based on a measurement value of the algae concentration sensor, a target gas supply amount is calculated based on the calculated target value for the concentration of the dissolved gas and the measured measurement value of the dissolved gas sensor, and the predetermined gas is supplied to the culture tank based on the calculated target gas supply amount.

9. A gas supply method using an algae culture apparatus having: a culture tank containing algae; a water quality sensor that measures one or more of the water temperature, organic carbon concentration, ammonia concentration, and phosphorus concentration in the culture tank; a dissolved gas sensor that measures the concentration of dissolved gas in the culture tank; and a gas supply amount adjustment unit that supplies a predetermined gas to the culture tank at an adjusted amount, characterized in that the gas supply method calculates a target value for the concentration of the dissolved gas based on a measurement value of the water quality sensor, calculates a target gas supply amount based on the calculated target value for the concentration of the dissolved gas and the measured measurement value of the dissolved gas sensor, and supplies the predetermined gas to the culture tank based on the calculated target gas supply amount.

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