JP7657690B2 - Cultivation method and culture device - Google Patents

Description

The present invention relates to a culture method and a culture device.

For example, as described in Patent Document 1, a culture method is known for culturing microalgae that can live by either autotrophic or heterotrophic nutrition. In this culture method, the density of the microalgae in the culture tank is first sufficiently increased by photoautotrophic cultivation, which causes the microalgae to perform photosynthesis. Then, organic matter is supplied to the microalgae to culture the microalgae heterotrophically. In this heterotrophic cultivation, most of the organic matter is consumed by the microalgae to be cultured, rather than by organisms that are not to be cultured, such as bacteria that have become mixed (contaminated) in the culture tank. This leads to an increase in the production volume of microalgae.

JP 2013-85534 A

However, for example, when culturing microalgae using a culture tank installed outdoors, the culture environment of the microalgae may change regardless of the cultivator's intention. In such a changing culture environment, it is difficult to perform photoautotrophic culture and heterotrophic culture under conditions suitable for each, simply by performing heterotrophic culture after photoautotrophic culture. For this reason, there is a concern that the production volume of microalgae may not be sufficiently improved.

The present invention aims to solve the above-mentioned problems.

One aspect of the present invention is a culture method for culturing microalgae in a changing culture environment, comprising a setting step of setting the nutritional form of the microalgae in accordance with the culture environment, and a culturing step of culturing the microalgae in the nutritional form set in the setting step. When photoautotrophy is set in the setting step, a gas containing carbon dioxide and light are supplied to the microalgae in the culturing step, and when heterotrophy is set in the setting step, organic matter is supplied to the microalgae in the culturing step.

Another aspect of the present invention is a culture device for culturing microalgae in a changing culture environment, comprising a culture tank for accommodating the microalgae and a culture solution, a setting unit for setting the nutritional form of the microalgae according to the culture environment, a gas supply unit for supplying a gas containing carbon dioxide to the culture tank when the setting unit sets photoautotrophy, and an organic matter supply unit for supplying organic matter to the culture tank when the setting unit sets heterotrophy.

With this culture method and culture device, the nutritional form of the microalgae can be set to suit the culture environment. Therefore, for example, when the culture environment is in conditions suitable for photoautotrophic culture, the microalgae can be cultured photoautotrophically. Also, when the culture environment is in conditions suitable for heterotrophic culture, the microalgae can be cultured heterotrophically. In this way, by culturing the microalgae in a nutritional form that suits the culture environment, the production volume of the microalgae can be improved.

FIG. 1 is a schematic explanatory diagram of a culture device according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the amount of solar radiation and the production amount of microalgae for each of photoautotrophy and heterotrophy. FIG. 3 is a flowchart illustrating an example of a culture method according to an embodiment of the present invention. 4A and 4B are graphs showing the relationship between the amount of dissolved inorganic carbon in the culture solution and the time elapsed since the supply of gas to the culture tank was stopped, respectively. FIG. 5 is a flowchart illustrating a culture method according to a modified example.

The culture device 10 according to this embodiment shown in FIG. 1 includes a culture tank 12 capable of containing a culture solution and microalgae. In the culture device 10, microalgae are cultured in the culture solution contained in the culture tank 12. The culture solution preferably contains water and nutrients necessary for culturing microalgae (e.g., nitrogen, phosphorus, potassium, etc.).

The microalgae cultured in the culture device 10 can live by either photoautotrophy or heterotrophy. Photoautotrophy is a method of nutrient intake in which the microalgae grow and proliferate by synthesizing organic matter on their own using light as an energy source and carbon dioxide as a carbon source (by performing photosynthesis). Heterotrophy is a method of nutrient intake in which the microalgae grow and proliferate by using organic matter taken in from the outside as a carbon source.

For example, when using cultured microalgae to produce biofuels such as ethanol, it is preferable to culture microalgae classified in the Chlorophyceae (e.g., Chlamydomonas, Chlorella), Prasinophyceae, Cryptophyceae, and Cyanobacteria (e.g., Spirulina) using the culture device 10. However, the microalgae that can be cultured using the culture device 10 are not limited to the above-mentioned microalgae.

The culture tank 12 may be any tank capable of housing microalgae and a culture solution. Therefore, the shape, material, and form of the culture tank 12 are not particularly limited. The culture tank 12 may be, for example, an open pond type or a photobioreactor. When the culture tank 12 is a photobioreactor, the culture tank 12 may be made of a material that is flexible and translucent, such as linear low density polyethylene (LLDPE). Note that translucency here refers to the ability to transmit light of the wavelengths required for the growth of microalgae.

The culture tank 12 is installed outdoors where it can receive sunlight, for example, as light with a wavelength (e.g., 340 to 700 nm) necessary for the growth of microalgae. The culture tank 12 may also be installed indoors where it can receive sunlight.

The culture tank 12 may be provided with a dissolved inorganic carbon amount detection unit (not shown) capable of detecting the amount of dissolved inorganic carbon in the culture solution contained in the culture tank 12. The culture tank 12 may also be provided with an in-tank organic matter amount detection unit (not shown) capable of detecting the amount of organic matter contained in the culture solution contained in the culture tank 12.

In addition to the culture tank 12, the culture device 10 includes a control unit 14, a gas supply unit 16, an organic matter supply unit 18, and a distribution unit 20. The control unit 14 is configured as a microcomputer including, for example, a CPU (not shown), and performs various processes and controls related to the culture device 10 by executing predetermined calculations according to a control program. The control unit 14 includes a setting unit 22 and a predicted value acquisition unit 24.

The setting unit 22 sets the nutritional form of the microalgae according to the culture environment. In this embodiment, the setting unit 22 sets the nutritional form according to, for example, the amount of solar radiation irradiated to the microalgae (hereinafter also simply referred to as the amount of solar radiation) as the culture environment. In this case, the setting unit 22 compares the amount of solar radiation with a solar radiation reference value P, and sets photoautotrophy when the amount of solar radiation exceeds the solar radiation reference value P. Furthermore, the setting unit 22 sets heterotrophy when the amount of solar radiation is equal to or less than the solar radiation reference value P.

As shown in FIG. 2, when culturing microalgae photoautotrophically, the greater the amount of solar radiation, the greater the amount of microalgae produced by the culture (hereinafter also referred to as unit production amount). In other words, with photoautotrophy, the less the amount of solar radiation, the less the production amount. On the other hand, when culturing microalgae heterotrophically, the production amount is constant regardless of whether the amount of solar radiation increases or decreases. Therefore, as shown in FIG. 2, when the amount of solar radiation exceeds the solar radiation reference value P, the amount of production by photoautotrophy exceeds the amount of production by heterotrophy. In other words, when the amount of solar radiation is equal to or less than the solar radiation reference value P, the amount of production by photoautotrophy is equal to or less than the amount of production by heterotrophy. In other words, the solar radiation reference value P is the amount of solar radiation when the amount of production by photoautotrophy becomes equal to or less than the amount of production by heterotrophy.

In this embodiment, the setting unit 22 in FIG. 1 compares the solar radiation prediction value acquired by the predicted value acquisition unit 24 with the solar radiation reference value P to set the nutritional format. The predicted value acquisition unit 24 acquires information on the amount of solar radiation, such as the weather at the time of cultivation, the time at the time of cultivation, and the season at the time of cultivation, from outside. The predicted value acquisition unit 24 predicts the amount of solar radiation at the time of cultivation based on the information on the amount of solar radiation acquired from outside. In this way, the predicted value acquisition unit 24 acquires the predicted amount of solar radiation. Note that the predicted value acquisition unit 24 may acquire a previously predicted predicted amount of solar radiation from outside, instead of acquiring the predicted amount of solar radiation by predicting the amount of solar radiation at the time of cultivation.

Specifically, the predicted value acquisition unit 24 obtains predicted solar radiation values D1 to D48 for each of 48 times T1 to T48, which are obtained by dividing the period from the start of the culture to 48 hours later into one-hour intervals. The setting unit 22 compares each of the predicted solar radiation values D1 to D48 with the solar radiation reference value P to set the nutrient type for each of the times T1 to T48. As a result, the setting unit 22 creates a culture plan in which the nutrient type is set for each hour from the start of the culture to 48 hours later.

The culture plan is not limited to setting the nutrient type for each hour from the start of culture until 48 hours later. The setting unit 22 can create a culture plan by dividing an appropriate period into appropriate lengths according to the type of microalgae to be cultured, culture conditions including weather conditions, and the like, and setting the nutrient type for each division.

As shown in FIG. 1, when the setting unit 22 sets photoautotrophy, the gas supply unit 16 supplies gas containing carbon dioxide gas to the culture tank 12 via the distribution unit 20. The gas may be only carbon dioxide gas, or may contain carbon dioxide gas and other gases, such as air. In this embodiment, the gas supply unit 16 supplies exhaust gas discharged from a factory as gas to the culture tank 12.

When the setting unit 22 sets heterotrophy, the organic matter supply unit 18 supplies organic matter to the culture tank 12 via the distribution unit 20. The organic matter here is a substance that microalgae can ingest and use to perform heterotrophy. In this embodiment, the organic matter supply unit 18 supplies organic matter contained in wastewater discharged from the drainage equipment to the culture tank 12. In this case, the organic matter supply unit 18 may perform a process to concentrate the organic matter in the wastewater discharged from the drainage equipment and then supply the organic matter to the culture tank 12. The organic matter supply unit 18 may also directly supply the wastewater discharged from the drainage equipment to the culture tank 12.

The distribution unit 20 adjusts the amount of gas supplied from the gas supply unit 16 and the amount of organic matter supplied from the organic matter supply unit 18 supplied to the culture tank 12 based on the control of the control unit 14. In this embodiment, the distribution unit 20 has a gas on-off valve 28 that opens and closes the gas flow path 26, and an organic matter on-off valve 32 that opens and closes the organic matter flow path 30. The gas flow path 26 is a flow path for supplying gas from the gas supply unit 16 to the culture tank 12. The organic matter flow path 30 is a flow path for supplying organic matter from the organic matter supply unit 18 to the culture tank 12.

The gas flow path 26 is preferably provided with a carbon dioxide gas detector 34 capable of detecting the carbon dioxide gas concentration in the exhaust gas. In addition, the organic matter flow path 30 is preferably provided with an in-flow organic matter amount detector 36 capable of detecting the amount of organic matter in the wastewater.

The gas on-off valve 28 is in an open state when the setting unit 22 sets photoautotrophy. The gas on-off valve 28 is in a closed state when the setting unit 22 sets heterotrophy. The gas on-off valve 28 may be configured to adjust the opening of the gas flow path 26.

The organic matter on-off valve 32 is closed when the setting unit 22 sets photoautotrophy. The organic matter on-off valve 32 is open when the setting unit 22 sets heterotrophy. The organic matter on-off valve 32 may be configured to adjust the opening of the organic matter flow path 30.

The control unit 14 controls the opening and closing of the gas on-off valve 28 and the organic matter on-off valve 32 of the distribution unit 20 based on the nutrient type set by the setting unit 22. This allows the setting of whether or not to supply gas to the culture tank 12. Also, it allows the setting of whether or not to supply organic matter to the culture tank 12. The setting unit 22 basically selects and sets either photoautotrophy or heterotrophy. In other words, in the culture device 10, basically, either gas or organic matter is selectively supplied to the culture tank 12. However, the setting unit 22 may set both photoautotrophy and heterotrophy in some cases. In other words, in the culture device 10, there may be a time when both gas and organic matter are supplied to the culture tank 12. Also, the setting unit 22 may not set either photoautotrophy or heterotrophy in some cases. In other words, in the culture device 10, there may be a time when both gas and organic matter are not supplied to the culture tank 12.

As described above, when culturing microalgae photoautotrophically in the culture device 10, sunlight (solar radiation) and exhaust gas discharged from the factory are used. When culturing microalgae heterotrophically in the culture device 10, organic matter contained in wastewater discharged from the drainage facility is used. The amount of solar radiation changes, for example, depending on the time (position of the sun), weather, season, etc. Also, for example, the amount of exhaust gas discharged from the factory and the concentration of carbon dioxide gas contained in the exhaust gas change depending on the operating status of the factory. Furthermore, for example, the amount of wastewater discharged from the drainage facility and the amount of organic matter contained in the wastewater change depending on the operating status of the drainage facility. In other words, the culture environment in which the culture device 10 cultivates microalgae changes.

The culture device 10 according to this embodiment is basically configured as described above. Below, with reference to the flowchart in FIG. 3, the culture method according to this embodiment will be described using an example in which it is carried out using the culture device 10 in FIG. 1. In this culture method, as described above, microalgae are cultured in a changing culture environment. Also, in this culture method, a nutrient form for culturing microalgae is set in accordance with the changing culture environment. Below, an example of a culture method for culturing microalgae by setting the nutrient form in accordance with changes in the amount of solar radiation as a change in the culture environment will be described.

In this cultivation method, first, a predicted value acquisition step is performed. In the predicted value acquisition step, a predicted solar radiation amount is acquired. The predicted solar radiation amount is a value that predicts the amount of solar radiation during cultivation of the microalgae. Specifically, in the predicted value acquisition step, the predicted solar radiation amount values D1 to D48 are obtained by the predicted value acquisition unit 24 as described above (step S1 in FIG. 3).

Next, a setting process is performed. In the setting process, the nutritional form of the microalgae is set according to the culture environment (amount of solar radiation). Specifically, in the setting process, the setting unit 22 in FIG. 1 compares each of the predicted solar radiation values D1 to D48 with the solar radiation reference value P as described above to create a culture plan (step S2 in FIG. 3).

Next, the culture process is performed. In the culture process, the microalgae are cultured in the nutritional form set in the setting process. Specifically, as shown in step S3 of FIG. 3, it is confirmed whether the current time Tn, which corresponds to any of T1 to T48, is set to photoautotrophy in the culture plan.

If it is confirmed in step S3 that the current time Tn is set to photoautotrophy (step S3: YES), the process proceeds to step S4 in FIG. 3, where gas is supplied from the gas supply unit 16 to the culture tank 12 via the distribution unit 20. At this time, sunlight is irradiated onto the microalgae in the culture tank 12. In addition, the supply of organic matter to the culture tank 12 is stopped. As a result, the microalgae are cultivated by photoautotrophy.

When the current time Tn is set to photoautotrophy in the cultivation plan, the amount of solar radiation on the microalgae exceeds the solar radiation reference value P. Therefore, by culturing microalgae photoautotrophically, it is possible to increase the production amount of microalgae compared to culturing microalgae heterotrophically.

Next, proceed to step S5 in FIG. 3 to check whether the next time Tn+1 after the current time Tn is set to heterotrophy in the culture plan. If it is confirmed in step S5 that the next time Tn+1 is not set to heterotrophy (is set to photoautotrophy) (step S5: NO), return to step S3 to continue the culture process.

If it is confirmed in step S5 that the next time Tn+1 is set to heterotrophy (step S5: YES), proceed to step S6 in FIG. 3. In step S6, the remaining time Tx from the current time until the next time Tn+1 is calculated.

Next, proceed to step S7 in FIG. 3. In step S7, it is determined whether the remaining time Tx has reached the gas grace period Tc1. Here, as shown in FIG. 4A, when the supply of gas to the culture tank 12 is stopped, the concentration of gas dissolved in the culture solution (amount of dissolved inorganic carbon) decreases as the time that elapses with the gas supply stopped increases. This is because, for example, the dissolved inorganic carbon is consumed by the microalgae. The gas grace period Tc1 is the time from when the supply of gas to the culture tank 12 is stopped until the amount of dissolved inorganic carbon reaches the lower limit of the amount of dissolved inorganic carbon required for the microalgae to perform photoautotrophy.

For this reason, in the culture process, for example, when switching the nutritional form from photoautotrophy to heterotrophy, it is preferable to stop the supply of gas to the culture tank 12 and then start the supply of organic matter to the culture tank 12 before the gas grace period Tc1 has elapsed. This makes it possible to avoid a time when the microalgae cannot perform either photoautotrophy or heterotrophy. This in turn makes it possible to increase the production amount of microalgae.

When the remaining time Tx reaches the gas grace period Tc1, the gas supply is stopped and the organic matter supply is started. This makes it possible to quickly transition to heterotrophy when the next time Tn+1 is reached. By switching the gas and organic matter supply in advance in this way, it is easier to bring the amount of gas and the amount of organic matter in the culture solution to values suitable for heterotrophy when the next time Tn+1 is reached. On the other hand, by maintaining the gas and organic matter supply without switching until the remaining time Tx reaches the gas grace period Tc1, it is possible to avoid interfering with photoautotrophic cultivation at the current time Tn.

Therefore, if it is determined in step S7 of FIG. 3 that the remaining time Tx is longer than the gas grace period Tc1 (step S7: NO), the processes of steps S6 and S7 are repeated until the remaining time Tx reaches the gas grace period Tc1.

If it is determined in step S7 that the remaining time Tx has reached the gas grace period Tc1 (step S7: YES), the process proceeds to step S8 in FIG. 3. In step S8, gas supply from the gas supply unit 16 to the culture tank 12 via the distribution unit 20 is stopped. Also, organic matter supply from the organic matter supply unit 18 to the culture tank 12 via the distribution unit 20 is started. As a result, the culture is switched to heterotrophic culture.

When culturing microalgae heterotrophically, a shielding section (not shown) for blocking sunlight may be provided in the culture tank 12. This prevents light from being supplied to the microalgae. As a result, it becomes possible to more effectively cultivate the microalgae heterotrophically.

During the time set for heterotrophy in the cultivation plan, the amount of solar radiation on the microalgae is equal to or less than the solar radiation reference value P. Therefore, by culturing the microalgae heterotrophically, the production amount of the microalgae can be increased compared to culturing the microalgae photoautotrophically. After the processing of step S8, the process returns to step S3 to continue the cultivation process.

If it is confirmed in step S3 that the current time Tn is not set to photoautotrophy (is set to heterotrophy) (step S3: NO), the process proceeds to step S9 in FIG. 3. In step S9, organic matter is supplied from the organic matter supply unit 18 to the culture tank 12 via the distribution unit 20. At this time, gas supply to the culture tank 12 is stopped. As a result, the microalgae are cultivated by heterotrophy.

When the current time Tn is set to heterotrophy in the cultivation plan, the amount of solar radiation on the microalgae is equal to or less than the solar radiation reference value P. Therefore, by culturing the microalgae heterotrophically, the production amount of the microalgae can be increased compared to culturing the microalgae photoautotrophically.

Next, proceed to step S10 in FIG. 3 to check whether the next time Tn+1 after the current time Tn is set to photoautotrophy in the culture plan. If it is confirmed in step S10 that the next time Tn+1 is not set to photoautotrophy (is set to heterotrophy) (step S10: NO), return to step S3 to continue the culture process.

If it is confirmed in step S10 that the next time Tn+1 is set to photoautotrophy (step S10: YES), proceed to step S11 in FIG. 3. In step S11, the remaining time Tx from the current time until the next time Tn+1 is calculated.

Next, proceed to step S12 in FIG. 3. In step S12, it is determined whether the remaining time Tx has reached the organic matter grace period Tc2. Here, as shown in FIG. 4B, when the supply of organic matter to the culture tank 12 is stopped, the amount of organic matter in the culture solution decreases the longer the time that the supply of organic matter is stopped. This is because, for example, the organic matter is consumed by the microalgae. The organic matter grace period Tc2 is the time from when the supply of organic matter to the culture tank 12 is stopped until the amount of organic matter in the culture solution reaches the lower limit of the amount of organic matter required for the microalgae to perform heterotrophy.

For this reason, in the culture process, for example, when switching the nutritional form from heterotrophy to photoautotrophy, it is preferable to stop the supply of organic matter to the culture tank 12 and then start the supply of gas to the culture tank 12 before the organic matter grace period Tc2 has elapsed. This makes it possible to avoid a time during which the microalgae cannot perform either heterotrophy or photoautotrophy. This in turn makes it possible to increase the production amount of microalgae.

Furthermore, when the remaining time Tx reaches the organic matter grace period Tc2, the supply of organic matter is stopped and the supply of gas is started. This makes it possible to quickly transition to photoautotrophy when the next time Tn+1 is reached. By switching the supply of gas and organic matter in advance in this way, it is easier to bring the amount of gas and the amount of organic matter in the culture solution to values suitable for photoautotrophy when the next time Tn+1 is reached. On the other hand, by maintaining the supply of gas and organic matter without switching until the remaining time Tx reaches the organic matter grace period Tc2, it is possible to avoid interfering with heterotrophic cultivation at the current time Tn.

Therefore, if it is determined in step S12 of FIG. 3 that the remaining time Tx is longer than the organic matter grace period Tc2 (step S12: NO), the processes of steps S11 and S12 are repeated until the remaining time Tx reaches the organic matter grace period Tc2.

If it is determined in step S12 that the remaining time Tx has reached the organic matter grace period Tc2 (step S12: YES), the process proceeds to step S13 in FIG. 3. In step S13, the supply of organic matter from the organic matter supply unit 18 to the culture tank 12 via the distribution unit 20 is stopped. Also, gas supply from the gas supply unit 16 to the culture tank 12 via the distribution unit 20 is started. As a result, the culture is switched to photoautotrophic culture.

During the time set for photoautotrophy in the cultivation plan, the amount of sunlight reaching the microalgae exceeds the standard sunlight value P. Therefore, by culturing the microalgae photoautotrophically, the production volume of the microalgae can be increased compared to culturing the microalgae heterotrophically. After the processing of step S13, the processing from step S3 onwards is repeated.

In the above culture process, the microalgae are cultured until the times T1 to T48 set in the culture plan have elapsed, and then the flowchart according to this embodiment ends. Note that after the microalgae are cultured until the times T1 to T48 have elapsed, the culture process may be ended and the microalgae may be collected together with the culture liquid from the culture tank 12. In this case, the cultured microalgae can be obtained by separating the microalgae from the culture liquid.

After culturing the microalgae for times T1 to T48, the predicted value acquisition process of step S1 and the setting process of step S2 may be performed again. In this case, the culturing process is continued based on the newly created culturing plan. By culturing the microalgae in this manner, the microalgae are sufficiently proliferated in the culture tank 12, and then the microalgae are collected together with the culture fluid from inside the culture tank 12. The cultured microalgae can then be obtained by separating the microalgae from the culture fluid.

As described above, in the culture device 10 and culture method according to this embodiment, the nutritional form of the microalgae can be set to match the culture environment. Therefore, for example, when the culture environment is in a condition suitable for photoautotrophic culture, the microalgae can be cultured photoautotrophically. Also, when the culture environment is in a condition suitable for heterotrophic culture, the microalgae can be cultured heterotrophically. In this way, by culturing the microalgae in a nutritional form that matches the culture environment, the production volume of the microalgae can be increased effectively.

In the culture method according to the above embodiment, in the setting process, the nutrition type is set according to the amount of solar radiation irradiated to the microalgae as the culture environment, and when the amount of solar radiation exceeds the solar radiation reference value P, photoautotrophy is selected, and when the amount of solar radiation is equal to or less than the solar radiation reference value P, heterotrophy is selected.

In the culture device 10 according to the above embodiment, the culture tank 12 is installed so that it can receive sunlight, and the setting unit 22 sets the nutrition type according to the amount of solar radiation irradiated to the microalgae as the culture environment, and when the amount of solar radiation exceeds the solar radiation reference value P, the setting unit 22 sets photoautotrophy, and when the amount of solar radiation is equal to or less than the solar radiation reference value P, the setting unit 22 sets heterotrophy.

In these cases, the nutritional form that produces the highest amount of microalgae can be set according to the amount of sunlight during cultivation. This allows the production of microalgae to be increased effectively.

In the culture method according to the above embodiment, a predicted value acquisition step is performed before the setting step to acquire a predicted solar radiation value that predicts the amount of solar radiation during the culture of the microalgae, and in the setting step, the nutrient form is set based on the predicted solar radiation value.

The culture device 10 according to the above embodiment is provided with a predicted value acquisition unit 24 that acquires a predicted solar radiation value that predicts the amount of solar radiation during the culture of microalgae, and the setting unit 22 sets the nutrient type based on the predicted solar radiation value.

In these cases, for example, before the time Tn+1 following the current time Tn, preparations can be made to switch to the nutrient form set for the next time Tn+1. This makes it possible to smoothly switch nutrient forms. As a result, the production volume of microalgae can be increased satisfactorily.

In the culture method according to the above embodiment, the gas supplied to the microalgae in the culture process is exhaust gas discharged from the factory, and the organic matter supplied to the microalgae in the culture process is contained in the wastewater discharged from the drainage facility.

In the culture device 10 according to the above embodiment, the gas supply unit 16 supplies exhaust gas discharged from the factory as gas to the culture tank 12, and the organic matter supply unit 18 supplies organic matter contained in wastewater discharged from the drainage facility to the culture tank 12.

Factory exhaust gas is supplied to the culture tank 12, and the carbon dioxide gas contained in the exhaust gas is used to cultivate microalgae. This prevents the carbon dioxide gas in the exhaust gas from being directly released into the atmosphere. In this case, it becomes easier to process the carbon dioxide gas in the exhaust gas. This in turn makes it possible to contribute to measures against global warming.

In addition, organic matter contained in the wastewater from the drainage system is supplied to the culture tank 12 and used to cultivate microalgae. This makes it easier to treat the organic matter in the wastewater, which in turn contributes to the conservation of the water environment.

The present invention is not limited to the above-described embodiment, and various configurations may be adopted without departing from the gist of the present invention.

For example, the culture device 10 according to the above embodiment includes a predicted value acquisition unit 24, and the setting unit 22 sets the nutrient format based on the predicted solar radiation value acquired by the predicted value acquisition unit 24. However, instead of the predicted solar radiation value, the setting unit 22 may set the nutrient format by, for example, comparing the measured solar radiation value Dr with the solar radiation reference value P. The measured solar radiation value Dr is, for example, the amount of solar radiation during culture measured in real time by a solar radiation sensor (solar radiation measurement unit) (not shown) provided in the culture tank 12.

In addition, in the setting process of the culture method according to the above embodiment, the nutrition type is set based on the predicted solar radiation value. However, in the setting process, the nutrition type may be set based on the measured solar radiation value Dr. In this case, for example, the culture process may include a solar radiation measurement process instead of a predicted value acquisition process.

In other words, in the culture method according to the modified example, for example, as shown in the flowchart of FIG. 5, a solar radiation measurement step is first performed. In the solar radiation measurement step, the amount of solar radiation during culture is measured to obtain a solar radiation measurement value Dr (step S20 in FIG. 5).

Next, a setting process is performed. In the setting process, it is determined whether the measured solar radiation amount Dr exceeds the solar radiation reference value P (step S21 in FIG. 5). If it is determined in step S21 that the measured solar radiation amount Dr exceeds the solar radiation reference value P (step S21: YES), the process proceeds to step S22 in FIG. 5 to set photoautotrophy.

Next, proceed to step S23 in FIG. 5 to perform the culture process. In the culture process, gas is supplied from the gas supply unit 16 to the culture tank 12 via the distribution unit 20. At this time, the supply of organic matter to the culture tank 12 is stopped. As a result, the microalgae are cultured by photoautotrophy.

If it is determined in step S21 that the measured solar radiation value Dr is equal to or less than the solar radiation reference value P (step S21: NO), the process proceeds to step S24 in FIG. 5 to set heterotrophy.

Then, proceed to step S25 in FIG. 5 to perform the culture process. In the culture process, organic matter is supplied from the organic matter supply unit 18 to the culture tank 12 via the distribution unit 20. At this time, gas supply to the culture tank 12 is stopped. As a result, the microalgae are cultured by heterotrophy.

After the processing of step S23 or step S25 is completed, the process returns to step S20 and the solar radiation measurement process is performed. By culturing the microalgae in this manner, the microalgae are sufficiently grown in the culture tank 12, and then the microalgae are collected together with the culture liquid from inside the culture tank 12. The cultured microalgae can then be obtained by separating the microalgae from the culture liquid.

From the above, in the culture device 10 and culture method according to the modified example, the nutritional form that produces a higher production volume of microalgae can be set according to the measured solar radiation value Dr, which is the amount of solar radiation actually used during culture. This makes it possible to effectively increase the production volume of microalgae.

The culture device 10 may include both a predicted value acquisition unit 24 and a solar radiation sensor (sun radiation measurement unit). In this case, it is preferable that the setting unit 22 creates a culture plan as described above and then modifies the culture plan using the measured solar radiation value Dr.

The setting unit 22 of the culture device 10 according to the above embodiment sets the nutrient type according to the amount of solar radiation as the culture environment. Also, in the setting process of the culture method according to the above embodiment, the nutrient type is set according to the amount of solar radiation as the culture environment. However, the present invention is not limited to these.

The setting unit 22 of the culture device 10 may set the nutrient type according to at least one of the amount of exhaust gas discharged from the factory and the amount of wastewater discharged from the drainage facility as the culture environment.

In the process of setting the culture method, the nutrient form may be set according to at least one of the amount of exhaust gas discharged from the factory and the amount of wastewater discharged from the drainage facility as the culture environment.

The setting unit 22 sets photoautotrophy when at least one of the amount of exhaust gas and the concentration of carbon dioxide gas contained in the exhaust gas increases, for example, depending on the operating conditions of the factory. Specifically, photoautotrophy is set when the concentration of carbon dioxide gas detected by the carbon dioxide gas detection unit 34 exceeds the gas standard value. This allows the carbon dioxide gas in the exhaust gas to be actively used for culturing microalgae. As a result, the production volume of microalgae can be increased. In addition, it is possible to contribute to measures against global warming by making it easier to process the carbon dioxide gas in the exhaust gas.

The setting unit 22 sets heterotrophy when at least one of the amount of wastewater and the amount of organic matter contained in the wastewater increases, for example, depending on the operating status of the drainage equipment. Specifically, heterotrophy is set when the amount of organic matter detected by the organic matter amount detection unit 36 in the flow path exceeds the organic matter standard value. This allows the organic matter in the wastewater to be actively used for cultivating microalgae. As a result, the production volume of microalgae can be increased. In addition, it is possible to contribute to the conservation of the water environment by making it easier to treat the organic matter in the wastewater.

The setting unit 22 can also set the nutrition type according to the culture environment that combines two or more selected from the amount of solar radiation, the amount of exhaust gas discharged from the factory, and the amount of wastewater discharged from the drainage facility. For example, the setting unit 22 may set both photoautotrophy and heterotrophy when the predicted value of the amount of solar radiation or the measured value of solar radiation during culture is greater than the solar radiation reference value P and the amount of organic matter detected by the organic matter amount detection unit 36 in the flow path exceeds the organic matter reference value. In this case, gas is supplied to the culture tank 12 from the gas supply unit 16, and organic matter is supplied from the organic matter supply unit 18. As a result, the production amount of microalgae can be improved. In addition, the carbon dioxide gas in the exhaust gas can be easily treated. Furthermore, the organic matter in the wastewater can be easily treated.

In the above embodiment, the culture tank 12 is installed so that it can receive sunlight. However, as described above, when the nutrient type is set according to at least one of the amount of exhaust gas discharged from the factory and the amount of wastewater discharged from the drainage facility as the culture environment, the culture tank 12 does not need to be able to receive sunlight. The culture tank 12 may be installed so that it can receive artificial light of a wavelength (e.g., 340 to 700 nm) required for the growth of microalgae instead of sunlight. In this case, for example, when photoautotrophy is set by the setting unit 22, artificial light is irradiated to the culture tank 12. On the other hand, when heterotrophy is set by the setting unit 22, irradiation of artificial light to the culture tank 12 is stopped.

The gas supply unit 16 is not limited to supplying exhaust gas discharged from a factory to the culture tank 12. The gas supply unit 16 may supply gas other than exhaust gas discharged from a factory to the culture tank 12. The organic matter supply unit 18 is not limited to supplying organic matter contained in wastewater discharged from a drainage facility to the culture tank 12. The organic matter supply unit 18 may supply organic matter other than organic matter contained in wastewater discharged from a drainage facility to the culture tank 12.

10: Culture device 12: Culture tank 16: Gas supply unit 18: Organic matter supply unit 22: Setting unit 24: Predicted value acquisition unit P: Solar radiation reference value

Claims (4)

A culture method for culturing microalgae under a changing culture environment, comprising:
A setting step of setting the nutritional form of the microalgae according to the amount of solar radiation irradiated to the microalgae ;
A culture process for culturing the microalgae in the nutritional form set in the setting process;
A predicted value acquisition step of acquiring a predicted solar radiation amount value that predicts the solar radiation amount during the cultivation of the microalgae, prior to the setting step;
having
In the predicted value acquisition step, the solar radiation predicted value is acquired for each of the time periods obtained by dividing a predetermined period for culturing the microalgae into predetermined time periods,
In the setting step, a culture plan is created in which the nutrient form is set for each of the time segments based on the predicted solar radiation value,
In the setting step, photoautotrophy is set for the time period in which the predicted solar radiation amount exceeds a solar radiation reference value, and heterotrophy is set for the time period in which the predicted solar radiation amount is equal to or less than the solar radiation reference value.
When the photoautotrophy is set in the setting step, in the culturing step, a gas containing carbon dioxide and light are supplied to the culture tank containing the culture solution and the microalgae,
When the heterotrophic culture is set in the setting step, the culture step includes supplying organic matter to the culture tank ,
In the culturing step,
When switching the nutritional form from photoautotrophy to heterotrophy, when the remaining time (Tx) from the current time to the next division time (Tn+1) in the culture plan reaches the gas grace time (Tc1), the supply of the gas to the culture tank is stopped and the supply of the organic matter to the culture tank is started.
When switching the nutritional form from heterotrophy to photoautotrophy, when the remaining time from the current time to the next division time in the culture plan reaches the organic matter grace time (Tc2), the supply of the organic matter to the culture tank is stopped and the supply of the gas to the culture tank is started,
The gas grace period is the time from when the supply of the gas to the culture tank is stopped until the concentration of the gas dissolved in the culture solution reaches a lower limit concentration required for the microalgae to perform the photoautotrophy,
The organic matter grace period is the time from when the supply of the organic matter to the culture tank is stopped to when the amount of the organic matter in the culture solution reaches a lower limit of the amount of organic matter required for the microalgae to perform the heterotrophic process. The culture method according to claim 1 ,
The gas supplied to the microalgae in the culture process is exhaust gas discharged from a factory,
The culture method, wherein the organic matter supplied to the microalgae in the culture step is contained in wastewater discharged from a drainage facility. A culture device for culturing microalgae in a changing culture environment,
A culture tank that is installed so as to be able to receive sunlight and that contains the microalgae and a culture solution;
A setting unit that sets the nutritional form of the microalgae according to the amount of solar radiation irradiated to the microalgae ;
A gas supply unit that supplies a gas containing carbon dioxide to the culture tank when the setting unit sets photoautotrophy;
When the setting unit sets heterotrophy, an organic matter supplying unit that supplies organic matter to the culture tank;
A predicted value acquisition unit that acquires a predicted solar radiation amount value that predicts the solar radiation amount during the cultivation of the microalgae;
Equipped with
The predicted value acquisition unit acquires the solar radiation predicted value for each of the divided time periods obtained by dividing a predetermined period for culturing the microalgae into predetermined time periods,
The setting unit creates a culture plan in which the nutrient form is set for each of the time segments based on the predicted solar radiation value,
The setting unit sets the photoautotrophy for the time segment where the solar radiation predicted value exceeds a solar radiation reference value, and sets the heterotrophy for the time segment where the solar radiation predicted value is equal to or less than the solar radiation reference value.
When the nutritional form is switched from the photoautotrophic to the heterotrophic during the cultivation of the microalgae, when the remaining time (Tx) from the current time to the next division time (Tn+1) in the cultivation plan reaches the gas grace time (Tc1), the gas supply unit stops supplying the gas to the cultivation tank, and the organic matter supply unit starts supplying the organic matter to the cultivation tank;
When the nutritional form is switched from the heterotrophic to the photoautotrophic during the cultivation of the microalgae, when the remaining time from the current time to the next division time in the cultivation plan reaches the organic matter grace time (Tc2), the organic matter supply unit stops supplying the organic matter to the cultivation tank, and the gas supply unit starts supplying the gas to the cultivation tank;
The gas grace period is the time from when the supply of the gas to the culture tank is stopped until the concentration of the gas dissolved in the culture solution reaches a lower limit concentration required for the microalgae to perform the photoautotrophy,
A culture apparatus, wherein the organic matter grace period is the time from when the supply of the organic matter to the culture tank is stopped to when the amount of the organic matter in the culture solution reaches a lower limit of the amount of organic matter required for the microalgae to perform the heterotrophic process . In the culture apparatus according to claim 3 ,
The gas supply unit supplies exhaust gas discharged from a factory to the culture tank as the gas,
The organic matter supplying unit supplies the organic matter contained in wastewater discharged from a drainage facility to the culture tank.

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