Microbial cultivation system

Abstract

To provide a microbial cultivation system that can reduce an amount of a dissolution solution used to dissolve CO2 in biogas and improve safety.SOLUTION: A microbial cultivation system 1 includes: a methane fermentation tank 11 that biodegrades organic waste using methanogens to produce biogas containing methane and CO2; dissolution tanks 14A to 14C that dissolve the CO2 in the biogas produced by the methane fermentation tank 11 in a dissolution solution to increase the methane concentration in the biogas due to differences in relative solubility; culture tanks 16A to 16C that use the dissolution solution in which CO2 is dissolved to cultivate anoxygenic photosynthetic microorganisms under anaerobic conditions; and a circulation device 40 that circulates the dissolution solution in which CO2 is dissolved in the dissolution tanks 14A to 14C from the dissolution tanks 14A to 14C via the culture tanks 16A to 16C to the dissolution tanks 14A to 14C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a microbial culture system. [Background technology]

[0002] Conventionally, biogas, primarily composed of methane and CO2 (carbon dioxide), has been produced from organic waste through methane fermentation, and the produced methane has been used in boilers and gas-fired power generation, while the produced CO2 has been released into the atmosphere unused. Therefore, a technique for cultivating photosynthetic microorganisms and the like using the CO2 in the produced biogas is known. Examples of this type of technique include Patent Documents 1 to 4.

[0003] Patent Document 1 relates to a method of placing a culture solution and photosynthetic organisms in a culture tank, irradiating the culture tank with light and supplying a gas containing CO2, causing a photosynthetic reaction in the photosynthetic organisms to fix CO2. Patent Document 2 relates to a fermentation technology that generates biogas, mainly composed of methane and carbon dioxide, from organic waste.

[0004] Patent Document 3 describes a method for capturing and fixing CO2 from CO2-containing gas through a biochemical process that uses oxyhydrogen microorganisms or cell extracts containing enzymes derived from oxyhydrogen microorganisms. Patent Document 4 describes a methane fermentation apparatus that includes a methane fermentation tank that produces biogas by methane fermentation of organic waste, a gas storage means that stores the biogas produced in the methane fermentation tank, and a culture tank that cultures photosynthetic microorganisms. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-168463 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-207154 [Patent Document 3] JP 2018-200 A [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-3312 Summary of the Invention [Problem to be solved by the invention]

[0006] In a microbial culture system in which biogas containing methane and CO2, generated during the biodegradation of organic waste by methanogens, is supplied to photosynthetic microorganisms for cultivation, one issue is that a dissolving solution for dissolving CO2 must be continuously supplied from the outside to the dissolution tank or culture tank.In addition, when oxygenic photosynthetic microorganisms are used as culture microorganisms, there is a problem that a mixture of flammable gases, methane and oxygen, may occur.

[0007] However, the prior art does not adequately address the above-mentioned problems. In particular, the technology described in Patent Document 4 requires a continuous supply of alkaline electrolyzed water from the outside, and since oxygen-producing photosynthetic microorganisms are preferably used in the culture tank, contact between methane and oxygen is unavoidable. Therefore, the prior art has room for improvement in terms of reducing the amount of dissolved solution supplied to the system and improving safety.

[0008] An object of the present invention is to provide a microbial culture system that can reduce the amount of dissolving liquid used to dissolve CO2 in biogas and improve safety. [Means for solving the problem]

[0009] (1) The present invention provides a microbial culture system including: a methane fermentation tank that biodegrades organic waste with a methanogenic bacteria group to produce biogas containing methane and CO2; a dissolution tank that dissolves CO2 in the biogas produced in the methane fermentation tank in a dissolution solution to increase the methane concentration in the biogas due to a difference in relative solubility; a culture tank that uses the dissolution solution with dissolved CO2 to culture non-oxygenous photosynthetic microorganisms under anaerobic conditions; and a circulation device that circulates the dissolution solution with dissolved CO2 in the dissolution tank from the dissolution tank via the culture tank and back to the dissolution tank.

[0010] (2) In the microbial culture system of (1), a plurality of the dissolution tanks may be arranged in the flow path of the biogas produced by the methane fermentation tank, a plurality of the culture tanks may be arranged corresponding to the plurality of dissolution tanks, and the circulation device may independently perform the circulation treatment for each combination of the corresponding dissolution tank and culture tank.

[0011] (3) In the microbial culture system of (2), the timing at which the culture of the anoxygenic photosynthetic microorganisms is started may be different in each of the plurality of culture tanks.

[0012] (4) The microbial culture system of (3) may further include a gas flow path control device capable of changing the order in which the biogas passes through the plurality of dissolution tanks, and the gas flow path control device may change the order in which the biogas passes through the dissolution tanks so that the biogas first passes through the dissolution tank corresponding to the culture tank in the culture stage with a relatively large CO2 requirement among the plurality of culture tanks.

[0013] (5) In any one of the microorganism culture systems (1) to (4), the dissolution solution may be water containing 0.5% by mass or more and 4.0% by mass or less of sodium chloride.

[0014] (6) In any one of the microbial culture systems (1) to (4), the anoxygenic photosynthetic microorganism may be a marine purple photosynthetic bacterium.

[0015] (7) In any one of the microbial culture systems (1) to (4), the culture tank may have an airtight structure.

[0016] (8) In any of the microbial culture systems (1) to (4), a desulfurization device may be further provided, which is disposed in the flow path of the biogas produced in the methane fermentation tank and removes hydrogen sulfide contained in the biogas. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a microbial culture system that can reduce the amount of dissolving liquid used to dissolve CO2 in biogas and improve safety. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram showing a microbial culture system according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a circulation device and a gas flow path control device of the microorganism culture system according to the embodiment. [Figure 3] 1 is a graph showing the ideal methane concentration in biogas required in biogas utilization equipment. [Figure 4] 1 is a graph showing the change over time in the CO demand required in the culture tank. [Figure 5] This is a table showing the change over time in the CO2 requirement for each culture tank and the order of dissolution tanks through which biogas is aerated. [Figure 6] 1 is a graph showing the change over time in the CO2 requirement for each culture tank and the CO2 requirement for the entire system. [Figure 7] FIG. 10 is a schematic diagram of a circulation device and a gas flow path control device, showing the order in which biogas passes through a dissolution tank in the first control. [Figure 8] FIG. 10 is a schematic diagram of the circulation device and the gas flow path control device, showing the order in which biogas passes through the dissolution tank in the second control. [Figure 9] FIG. 10 is a schematic diagram of the circulation device and the gas flow path control device, showing the order in which biogas passes through the dissolution tank in the third control. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0020] <System configuration> 1 is a schematic diagram showing a microorganism culture system 1 according to one embodiment of the present invention. First, the overall configuration of the microorganism culture system 1 will be described with reference to FIG.

[0021] As shown in FIG. 1, the microbial culture system 1 of this embodiment mainly comprises a methane fermentation tank 11, a desulfurization device 12, dissolution tanks 14A to 14C, a gas holder 15, culture tanks 16A to 16C, and a dissolution liquid supply device 18.

[0022] The methane fermentation tank 11 biodegrades organic waste using methanogens in the tank to generate biogas containing methane and CO2 as its main components. The methane fermentation tank 11 is configured, for example, as a sealed tank that houses methanogens. The internal environment of the methane fermentation tank 11, such as the temperature and pH, is controlled so that the methanogens can reproduce.

[0023] The methane fermenter 11 of this embodiment is, for example, a digestion tank in which a substrate (sewage sludge, organic waste, etc.) is subjected to methane fermentation. This fermentation produces biogas and digested liquid.

[0024] The biogas produced in the methane fermentation tank 11 is sent by the blower 13 to the dissolution tanks 14A to 14C.

[0025] The digestive liquid produced in conjunction with the production of biogas in the methane fermentation tank 11 serves as a nutrient source for non-oxygen-producing photosynthetic microorganisms, so some or all of it may or may not be sent to the culture tanks 16A to 16C as needed.

[0026] The desulfurizer 12 is disposed in a biogas supply path connecting the methane fermentation tank 11 and the dissolution tanks 14A to 14C. The desulfurizer 12 performs a desulfurization process to remove hydrogen sulfide contained in the biogas. By removing hydrogen sulfide from the biogas by the desulfurizer 12, deterioration of the flow path material from the desulfurizer 12 to the dissolution tanks 14A to 14C is suppressed.

[0027] The gas flow path control device 20 controls the supply flow path of the biogas to the dissolution tanks 14A to 14C. In this embodiment, a plurality of dissolution tanks are arranged, for example, three dissolution tanks 14A to 14C are provided. The gas flow path control device 20 controls the supply flow path of the biogas to each of the dissolution tanks 14A to 14C. The detailed configuration of the gas flow path control device 20 will be described later.

[0028] The dissolution tanks 14A-14C increase the methane concentration in the biogas by dissolving CO2, which is contained in the biogas and has a relatively high solubility, in the dissolution liquid. In this embodiment, the biogas desulfurized in the desulfurization device 12 is blown into the dissolution tanks 14A-14C by a blower 13, which serves as an air blower, thereby performing a dissolution treatment using an aeration method. The dissolution treatment is performed as a multi-stage treatment using multiple dissolution tanks 14A-14C. As the biogas passes through the dissolution tanks 14A-14C in order, CO2 is dissolved in the dissolution liquid. The biogas, whose methane concentration has increased by passing through the dissolution tanks 14A-14C, is sent to the gas holder 15. The dissolution liquid stored in the dissolution tanks 14A-14C is the dissolution liquid circulated from the culture tanks 16A-16C by the circulation device 40.

[0029] The circulating lysate is not particularly limited as long as it does not inhibit the growth of anoxygenic photosynthetic microorganisms. The circulating lysate is preferably water containing 0.5% by mass to 4.0% by mass of sodium chloride, and more preferably seawater or a seawater substitute (artificial seawater, culture medium, etc.). In a preferred aspect of this embodiment, all of the lysates supplied to the system are such lysates.

[0030] The gas holder 15 stores the biogas that is produced in the methane fermentation tank 11 and whose methane concentration has increased in the dissolution tanks 14A to 14C. The biogas stored in the gas holder 15 is used as energy by the biogas utilization equipment 19.

[0031] In the culture tanks 16A to 16C, anoxygenic photosynthetic microorganisms, preferably marine purple photosynthetic bacteria, are cultured in seawater supplied as a dissolution solution by a dissolution solution supply device 18. Since the culture tanks 16A to 16C must be cultured under anaerobic conditions for the anoxygenic photosynthetic microorganisms, they are constructed as sealed water tanks with an airtight structure that prevents gas leakage.

[0032] When culturing oxygenic photosynthetic microorganisms using biogas, there is a risk of an explosive atmosphere being generated when the oxygen generated during photosynthesis comes into contact with the methane in the biogas. On the other hand, in the present invention, non-oxygenic photosynthetic microorganisms are used and the culture is carried out under anaerobic conditions using an airtight structure, so methane and oxygen do not mix within the culture tank, and the airtight structure prevents oxygen from being mixed in from outside, so an explosive atmosphere is not generated.

[0033] A solution in which CO2 from the biogas is dissolved in the dissolution tanks 14A to 14C is supplied to the culture tanks 16A to 16C from the methane fermentation tank 11. If necessary, digested liquid produced in the methane fermentation tank 11 may be supplied as a nutrient source together with the solution.

[0034] In the culture tanks 16A to 16C, anoxygenic photosynthetic microorganisms are cultured in the presence of CO2 (and digestive fluid, if necessary) using a solution in which CO2 has been dissolved. The cultured anoxygenic photosynthetic microorganisms can be recovered and used as various raw materials (fertilizer, feed, raw material for biopolymers, etc.). The anoxygenic photosynthetic microorganisms will be described later.

[0035] The circulation device 40 circulates the dissolution solution from the culture tanks 16A to 16C to the dissolution tanks 14A to 14C. The dissolution solution flowing from the culture tanks 16A to 16C to the dissolution tanks 14A to 14C may contain anoxygenic photosynthetic microorganisms and a small amount of CO2.

[0036] The circulation device 40 sends the dissolved solution in which CO2 has been dissolved in the dissolution tanks 14A to 14C to the culture tanks 16A to 16C, and then, after the CO2 has been consumed in the culture tanks 16A to 16C, the sent dissolved solution is returned to the dissolution tanks 14A to 14C by the transport of the pump 17. In the present invention, this series of circulation is referred to as "the lysis solution circulating from the lysis tank to the culture tank and then back to the lysis tank." The detailed configuration of the circulation device 40 will be described later.

[0037] The dissolution solution supplying device 18 supplies seawater as a dissolution solution to the dissolution tanks 14A-14C, and also supplies seawater to the culture tanks 16A-16C. As will be described later, seawater circulates between the dissolution tanks 14A-14C and the culture tanks 16A-16C, so the seawater supplied by the dissolution solution supplying device 18 does not need to be supplied all the time, but is supplied only initially or when there is a shortage of the dissolution solution. The dissolution solution supplying device 18 is composed of, for example, an on-off valve and a pump (not shown). Note that freshwater may be used as the dissolution solution depending on the type of anoxygenic photosynthetic microorganism cultured in the culture tanks 16A-16C.

[0038] <Circulation device> Next, the configuration of the circulation device 40 that circulates the dissolution solution between the dissolution tanks 14A to 14C and the culture tanks 16A to 16C will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing the configuration of the circulation device 40 and the gas flow path control device 20 of the microorganism culture system 1 of this embodiment. In Fig. 2, the pump 17 and the blower 13 described above are omitted. Note that the following description will be given taking as an example a case where seawater is used as the dissolution solution circulated by the circulation device 40 and marine purple photosynthetic bacteria are used as the anoxygenic photosynthetic microorganism.

[0039] 2, the number of dissolution tanks 14A to 14C is set to be the same as the number of culture tanks 16A to 16C. The circulation device 40 includes return lines 41A to 41C, delivery lines 42A to 42C, and circulation on-off valves 43A to 43C.

[0040] Between the dissolution tank 14A and the culture tank 16A, there are disposed a return line 41A that returns seawater from the dissolution tank 14A to the culture tank 16A, and a delivery line 42A that delivers seawater from the culture tank 16A to the dissolution tank 14A. A circulation on-off valve 43A is disposed on the delivery line 42A, and controls the supply of seawater from the culture tank 16A to the dissolution tank 14A by opening and closing it. Similarly, between the dissolution tank 14B and the culture tank 16B, there are disposed a return line 41B that returns seawater from the dissolution tank 14B to the culture tank 16B, and a delivery line 42B that delivers seawater from the culture tank 16B to the dissolution tank 14B. A circulation on-off valve 43B is disposed on the delivery line 42B, and controls the supply of seawater from the culture tank 16B to the dissolution tank 14B by opening and closing it. Between the dissolution tank 14C and the culture tank 16C, there are disposed a return line 41C for returning seawater from the dissolution tank 14C to the culture tank 16C, and a delivery line 42C for delivering seawater from the culture tank 16C to the dissolution tank 14C. A circulation on-off valve 43C is disposed on the delivery line 42C, and its opening and closing operation controls the supply of seawater from the culture tank 16C to the dissolution tank 14C.

[0041] As explained above, dissolution tank 14A is connected to correspond to culture tank 16A, dissolution tank 14B is connected to correspond to culture tank 16B, and dissolution tank 14C is connected to correspond to culture tank 16C. In this embodiment, the culture system of dissolution tank 14A and culture tank 16A, the culture system of dissolution tank 14B and culture tank 16B, and the culture system of dissolution tank 14C and culture tank 16C are each designed independently.

[0042] In order to minimize the power of the pump 17 to the extent of the loss in the piping, it is preferable to set the water depths of the dissolution tanks 14A to 14C and the culture tanks 16A to 16C to approximately the same depth.

[0043] <Gas flow path control device> Next, the configuration of the gas flow path control device 20 that controls the flow paths of the biogas supplied to the dissolution tanks 14A to 14C will be described. In this embodiment, the biogas is not simultaneously supplied to each of the dissolution tanks 14A to 14C. The reason why the biogas is not simultaneously supplied to the dissolution tanks 14A to 14C will be described.

[0044] Fig. 3 is a graph showing the ideal methane concentration in biogas required by the biogas utilization equipment 19. As shown in Fig. 3, in the biogas utilization equipment 19, the allowable range of fluctuation in the methane concentration in the biogas used as an energy source is determined, so it is preferable that the methane concentration in the biogas stored in the gas holder 15 be kept constant.

[0045] In the microorganism culture system 1 of this embodiment, CO2 is dissolved in seawater in the dissolution tanks 14A to 14C to increase the methane gas concentration of the biogas, and the biogas is then sent to the gas holder 15. To maintain a constant methane concentration in the biogas, it is preferable to maintain a constant amount of CO2 dissolved in the dissolution tanks 14A to 14C. In this regard, according to the configuration of this embodiment, the seawater in which CO2 has been dissolved in the dissolution tanks 14A to 14C is sent to the culture tanks 16A to 16C, and after the CO2 is consumed in the culture tanks 16A to 16C, the seawater is returned to the dissolution tanks 14A to 14C.

[0046] However, the CO2 demand in the culture tanks 16A to 16C depends on the amount of bacteria in the culture tanks 16A to 16C. Figure 4 is a graph showing the change over time in the CO2 demand required in the culture tanks 16A to 16C.

[0047] Here, the culture cycle performed in each of the culture tanks 16A-16C will be described. First, the on-off valve of the dissolution solution supply device 18 is opened, and seawater is supplied to the dissolution tanks 14A-14C and the culture tanks 16A-16C, and marine purple photosynthetic bacteria are introduced into the culture tanks 16A-16C. Next, a solution in which CO2 from the biogas is dissolved in the dissolution tanks 14A-14C is supplied from the methane fermentation tank 11 to the culture tanks 16A-16C. The marine purple photosynthetic bacteria in the culture tanks 16A-16C consume CO2 in the solution, and the solution with a reduced CO2 concentration is circulated to the dissolution tanks 14A-14C. This culture cycle is repeated. The marine purple photosynthetic bacteria gradually grow during the culture cycle, and the CO2 requirement increases as the marine purple photosynthetic bacteria grow. When marine purple photosynthetic bacteria decrease during the harvest period, the CO2 demand decreases in proportion to the bacterial mass.

[0048] In order to stably cultivate anoxygenic photosynthetic microorganisms and efficiently utilize biogas, it may be necessary to respond to fluctuations in CO2 demand during cultivation and to homogenize the methane concentration in the biogas generated after CO2 dissolution in the dissolution tank. Therefore, in this embodiment, the cultivation start timings of the multiple culture tanks 16A to 16C are staggered, and the timing of introducing biogas into the dissolution tanks 14A to 14C is switched by the gas flow path control device 20.

[0049] Returning to Figure 2, the specific configuration of the gas flow path control device 20 will be described. The gas flow path control device 20 is provided with a biogas supply path including a supply line 50, upstream branch lines 51A to 51C, downstream branch lines 52A to 52C, a junction line 53, and bypass lines 54A to 54C. The supply path is composed of piping or the like. The gas flow path control device 20 also includes first to ninth on-off valves 21 to 29 that control the flow of biogas flowing through the supply path. Next, the positional relationship between each line constituting the supply path and the first to ninth on-off valves 21 to 29 will be described.

[0050] The supply line 50 is configured such that its upstream end is connected to the methane fermentation tank 11 and its downstream end is branched into upstream branch lines 51A to 51C. Biogas discharged from the methane fermentation tank 11 is sent through the supply line 50 to the upstream branch lines 51A to 51C.

[0051] The upstream branch line 51A is configured so that its upstream end is connected to the supply line 50 and its downstream end is connected to the dissolution tank 14A. A first on-off valve 21 is disposed in the upstream branch line 51A. The upstream branch line 51B is configured so that its upstream end is connected to the supply line 50 and its downstream end is connected to the dissolution tank 14B. A second on-off valve 22 is disposed in the upstream branch line 51B. The upstream branch line 51C is configured so that its upstream end is connected to the supply line 50 and its downstream end is connected to the dissolution tank 14C. A third on-off valve 23 is disposed in the upstream branch line 51C.

[0052] The downstream branch line 52A is configured so that its upstream end is connected to the dissolution tank 14A and its downstream end is connected to the confluence line 53. An eighth on-off valve 28 is disposed in the downstream branch line 52A. The downstream branch line 52B is configured so that its upstream end is connected to the dissolution tank 14B and its downstream end is connected to the confluence line 53. A ninth on-off valve 29 is disposed in the downstream branch line 52B. The downstream branch line 52C is configured so that its upstream end is connected to the dissolution tank 14C and its downstream end is connected to the confluence line 53. A seventh on-off valve 27 is disposed in the downstream branch line 52C.

[0053] The confluence line 53 is connected to the downstream ends of the downstream branch lines 52A to 52C, and its downstream end is connected to the gas holder 15. The confluence line 53 delivers the biogas, whose methane gas concentration has increased through the dissolution tanks 14A to 14C, to the gas holder 15.

[0054] The bypass line 54A is configured such that its upstream end is connected to the upstream side of the eighth on-off valve 28 in the downstream branch line 52A and its downstream end is connected to the downstream side of the second on-off valve 22 in the upstream branch line 51B. A fifth on-off valve 25 is disposed in the bypass line 54A. The bypass line 54B is configured such that its upstream end is connected to the upstream side of the ninth on-off valve 29 in the downstream branch line 52B and its downstream end is connected to the downstream side of the third on-off valve 23 in the upstream branch line 51C. A sixth on-off valve 26 is disposed in the bypass line 54B. The bypass line 54C is configured such that its upstream end is connected to the upstream side of the seventh on-off valve 27 in the downstream branch line 52C and its downstream end is connected to the downstream side of the first on-off valve 21 in the upstream branch line 51A. A fourth on-off valve 24 is disposed in the bypass line 54C.

[0055] <Cultivation timing> When there are multiple culture tanks 16A to 16C, the amount of CO required can be shifted by shifting the culture timing of each culture tank 16A to 16C. Next, the culture timing when there are three culture tanks 16A to 16C will be described with reference to Figure 5. Figure 5 is a table showing the change over time in the amount of CO required for each culture tank 16A to 16C and the order of the dissolution tanks 14A to 14C through which biogas is aerated.

[0056] As shown in Figure 5, the timing of culturing is controlled so that the CO2 requirements of fermentors 16A to 16C are large, medium, or small. Specifically, the timing of starting culturing in fermentors 16A to 16C is controlled so that when the CO2 requirement of fermentor 16A is large, the CO2 requirement of fermentor 16B becomes medium, and the CO2 requirement of fermentor 16C becomes small. As shown in Figure 4, the CO2 requirements change over time. Therefore, when the CO2 requirement of fermentor 16A becomes small at the time of harvest, the CO2 requirement of fermentor 16B changes from medium to large, and the CO2 requirement of fermentor 16C changes from small to medium. When the CO2 requirement of fermentor 16A changes from small to medium, the CO2 requirement of fermentor 16B changes from large to small as the harvest progresses, and the CO2 requirement of fermentor 16C changes from medium to large. When the CO2 requirement of the culture tank 16A changes from medium to high again, the CO2 requirement of the culture tank 16B changes from small to medium, and the CO2 requirement of the culture tank 16C changes from large to small after the harvest time.

[0057] Figure 6 is a graph showing the change over time in the CO2 demand for each of the culture tanks 16A-16C and the CO2 demand for the entire system. As shown in Figure 6, by staggering the culture timing to account for bacterial growth, the CO2 demand for the entire system is leveled. Circulation between the dissolution tanks 14A-14C and the culture tanks 16A-16C is individually controlled for each tank, taking into account the balance between the CO2 supply rate from the dissolution tanks 14A-14C to the culture tanks 16A-16C and the CO2 consumption rate by the marine purple photosynthetic bacteria in the culture tanks 16A-16C. This circulation control can be a timer control method using a theoretically or experimentally determined change time, or a method that monitors the actual CO2 concentration and controls based on the measured value.

[0058] <Biogas aeration timing> The culture tanks 16A to 16C correspond to the dissolution tanks 14A to 14C, respectively. Furthermore, the dissolution tanks 14A to 14C of this embodiment process biogas in multiple stages, serially rather than in parallel, so that a large amount of CO2 is dissolved in the culture tank 16A to 16C that is first aerated with biogas. Therefore, by controlling the timing of aeration of biogas in each of the dissolution tanks 14A to 14C in accordance with the required amount of CO2, which is determined by the culture timing of each of the culture tanks 16A to 16C, the amount of CO2 dissolved in each of the dissolution tanks 14A to 14C can be equalized.

[0059] In this embodiment, the order of the dissolution tanks 14A to 14C through which the biogas is aerated is controlled by the gas flow path control device 20 so that the dissolution amount corresponds to the CO2 requirement of each of the culture tanks 16A to 16C. The gas flow path control device 20 controls the route through which the biogas is aerated by switching the first to ninth on-off valves 21 to 29 between open and closed states, thereby changing the order in which the biogas is aerated through the culture tanks 16A to 16C.

[0060] In the following explanation, the control of the gas flow path control device 20 that causes the biogas to pass through the dissolution tank 14A, 14B, and 14C in this order is referred to as first control. The control of the gas flow path control device 20 that causes the biogas to pass through the dissolution tank 14B, 14C, and 14A in this order is referred to as second control. The control of the gas flow path control device 20 that causes the biogas to pass through the dissolution tank 14C, 14B, and 14A in this order is referred to as third control. The first to third controls are switched by controlling the opening and closing of the first to ninth on-off valves 21 to 29.

[0061] Referring to Figure 7, consider the aeration timing when the CO2 requirement of culture tank 16A is high, the CO2 requirement of culture tank 16B is medium, and the CO2 requirement of culture tank 16C is low. In this state, the first control is applied to the gas flow path control device 20. Figure 7 is a schematic diagram of the circulation device 40 and the gas flow path control device 20, showing the order in which the biogas passes through the dissolution tanks 14A to 14C under the first control.

[0062] In the first control, the first on-off valve 21, the fifth on-off valve 25, the sixth on-off valve 26, and the seventh on-off valve 27 are controlled to be open, and the second on-off valve 22, the third on-off valve 23, the fourth on-off valve 24, the eighth on-off valve 28, and the ninth on-off valve 29 are controlled to be closed. As a result, the biogas is aerated in the order of dissolution tank 14A, dissolution tank 14B, and dissolution tank 14C. In the first control, the amount of CO2 dissolved is large in dissolution tank 14A corresponding to fermentor 16A with a large demand, the amount of CO2 dissolved is medium in dissolution tank 14B corresponding to fermentor 16B with a medium demand, and the amount of CO2 dissolved is small in dissolution tank 14C corresponding to fermentor 16C with a small demand.

[0063] Referring to Figure 8, consider the aeration timing when the CO2 requirement of culture tank 16A is small, the CO2 requirement of culture tank 16B is large, and the CO2 requirement of culture tank 16C is medium. In this state, the second control is applied to the gas flow path control device 20. Figure 8 is a schematic diagram of the circulation device 40 and the gas flow path control device 20, showing the order in which the biogas passes through the dissolution tanks 14A to 14C under the second control.

[0064] In the second control, the second on-off valve 22, the fourth on-off valve 24, the sixth on-off valve 26, and the eighth on-off valve 28 are controlled to be open, and the first on-off valve 21, the third on-off valve 23, the fifth on-off valve 25, the seventh on-off valve 27, and the ninth on-off valve 29 are controlled to be closed. As a result, the biogas is aerated in the order of dissolution tank 14B, dissolution tank 14C, and dissolution tank 14A. In the second control, the amount of CO2 dissolved in dissolution tank 14A corresponding to fermentor 16A with a small demand is small, the amount of CO2 dissolved in dissolution tank 14B corresponding to fermentor 16B with a large demand is large, and the amount of CO2 dissolved in dissolution tank 14C corresponding to fermentor 16C with a medium demand is medium.

[0065] Referring to Figure 9, consider the aeration timing when the CO2 requirement of culture tank 16A is medium, the CO2 requirement of culture tank 16B is small, and the CO2 requirement of culture tank 16C is large. In this state, the third control is applied to the gas flow path control device 20. Figure 9 is a schematic diagram of the circulation device 40 and the gas flow path control device 20, showing the order in which the biogas passes through the dissolution tanks 14A to 14C under the third control.

[0066] In the third control, the third on-off valve 23, the fourth on-off valve 24, the fifth on-off valve 25, and the ninth on-off valve 29 are controlled to be open, and the first on-off valve 21, the second on-off valve 22, the sixth on-off valve 26, the seventh on-off valve 27, and the eighth on-off valve 28 are controlled to be closed. As a result, the biogas is aerated in the order of dissolution tank 14C, dissolution tank 14B, and dissolution tank 14A. In the third control, the amount of CO2 dissolved in dissolution tank 14A corresponding to fermentor 16A with a medium demand is medium, the amount of CO2 dissolved in dissolution tank 14B corresponding to fermentor 16B with a small demand is small, and the amount of CO2 dissolved in dissolution tank 14C corresponding to fermentor 16C with a large demand is large.

[0067] 5, the gas flow path control device 20 repeatedly performs the first control, the second control, and the third control in this order. The timing of switching from the first control to the second control, the timing of switching from the second control to the third control, and the timing of switching from the third control to the first control are set according to changes in the CO demand of each of the culture tanks 16A to 16C.

[0068] Alternatively, a CO2 sensor may be placed at the outlet of each of the dissolution tanks 14A to 14C, and the number of dissolution tanks 14A to 14C to be vented may be changed based on the CO2 concentration measured by the CO2 sensor. For example, if two units are sufficient to dissolve CO2, the flow path may be controlled so that biogas is vented only to dissolution tanks 14A and 14B.

[0069] <Culture tank> The culture tank is configured to be capable of culturing anoxygenic photosynthetic microorganisms. As described above, in the present invention, an airtight tank is used for culturing under anaerobic conditions.

[0070] Although there are no particular limitations on the non-oxygenic photosynthetic microorganism, from the viewpoint of efficiently promoting the fermentation system of the present invention, those having bacteriochlorophyll as a photosynthetic pigment are preferred, including bacteriochlorophyll a, bacteriochlorophyll g, bacteriochlorophyll b, and bacteriochlorophyll c.

[0071] Preferred anoxygenic photosynthetic microorganisms are those that have bacteriochlorophyll as a photosynthetic pigment, are halophilic, and can grow in an environment with a sodium chloride concentration of about 0.5% by mass or more and 4.0% by mass or less.

[0072] Marine purple photosynthetic bacteria are particularly preferred as anoxygenic photosynthetic microorganisms. Marine purple photosynthetic bacteria are bacteria that can use seawater, nitrogen, carbon dioxide (CO2), light, etc. for growth, and can perform nonoxygenic photosynthesis using CO2 under near-infrared light and fix atmospheric nitrogen using nitrogenase.

[0073] The type of marine purple photosynthetic bacteria is not particularly limited, and examples include marine purple sulfur bacteria and marine non-sulfur purple bacteria.

[0074] Marine purple sulfur bacteria include bacteria of the genera Allochromatium, Ectothiorhodospira, Halochromatium, Halorhodospira, Marichromatium, Thiocapsa, Thiohalocapsa, and Thiophageococcus. More specifically, Marichromatium bheemlicum, Thiohalocapsa marina, and Thiophageococcus mangrovi are examples.

[0075] Marine purple non-sulfur bacteria include bacteria of the genera Rhodobaca, Rhodobacter, Rhodobium, Afifella (Rhodobium), Rhodothalassium, Rhodovulum, and Roseospira. More specifically, Rhodovulum sulfidophilum, Afifella marina, and Roseospira marina are examples.

[0076] In the above embodiment, marine purple photosynthetic bacteria are used as an example of anoxygenic photosynthetic microorganisms, but other oxygenic photosynthetic microorganisms may be selected. For example, if bacteria capable of treating hydrogen sulfide (e.g., purple sulfur photosynthetic bacteria) are used as anoxygenic photosynthetic microorganisms, the circulating dissolution solution will provide a desulfurization effect, and hydrogen sulfide can be reduced in the dissolution tanks 14A-14C. If hydrogen sulfide can be sufficiently treated within the microbial culture system 1, the capacity of the desulfurization device 12 can be reduced, or in some cases, the desulfurization device 12 itself can be omitted.

[0077] As described above, the microbial culture system 1 of this embodiment includes: a methane fermentation tank 11 that biodegrades organic waste using a methanogen group to produce biogas containing methane and CO2; dissolution tanks 14A to 14C that dissolve the CO2 in the biogas produced in the methane fermentation tank 11 in a dissolution solution to increase the methane concentration in the biogas due to a difference in relative solubility; culture tanks 16A to 16C that culture non-oxygenous photosynthetic microorganisms under anaerobic conditions using the dissolution solution with dissolved CO2; and a circulation device 40 that circulates the dissolution solution with dissolved CO2 in the dissolution tanks 14A to 14C from the dissolution tanks 14A to 14C via the culture tanks 16A to 16C to the dissolution tanks 14A to 14C.

[0078] This circulation significantly reduces the amount of dissolution solution required throughout the microbial culture system 1. Therefore, compared to the conventional technique of continuously supplying dissolution solution from an external source, the energy required to introduce dissolution solution into the dissolution tanks and culture tanks can be reduced. Furthermore, by aligning the water levels of the dissolution tanks 14A-14C and the culture tanks 16A-16C, the power required after the circulation process can be minimized to the extent equivalent to the loss in the piping. Furthermore, aeration generates a gas-liquid mixed flow, which also creates a CO2 concentration gradient, potentially leading to further power savings. Unlike the conventional technique, there is no need to continuously supply dissolution solution, etc., from an external source using a pressure head equivalent to the water depth to the dissolution tanks 14A-14C, which is advantageous in terms of energy efficiency. Furthermore, because anoxygenic photosynthetic microorganisms are cultivated, the risk of methane and oxygen mixing in the dissolution tanks 14A-14C and the culture tanks 16A-16C can be eliminated compared to the case of using oxygenic photosynthetic microorganisms. Furthermore, the culture tanks 16A to 16C have an airtight structure, and the culture is carried out in a closed system that is not exposed to the outside air, so that mixing of oxygen from the outside air can be prevented, further improving safety.

[0079] In addition, in this embodiment, multiple dissolution tanks 14A to 14C are arranged in the flow path of the biogas generated from the methane fermentation tank 11, multiple culture tanks 16A to 16C are arranged corresponding to the multiple dissolution tanks 14A to 14C, respectively, and the circulation device 40 independently performs circulation processing for each combination of the corresponding dissolution tank 14A to 14C and culture tank 16A to 16C.

[0080] This allows biogas to be dissolved using a multi-stage process, and even if contamination such as the proliferation of unintended bacterial species occurs in one of the multiple dissolution tanks 14A to 14C, contamination of the entire system can be prevented.

[0081] Furthermore, in this embodiment, the timing at which the cultivation of anoxygenic photosynthetic microorganisms is started is different in each of the plurality of culture tanks 16A to 16C.

[0082] This allows the culture tanks 16A to 16C to be at different culture stages, thereby suppressing fluctuations in the CO2 requirement of the entire system. By adjusting the timing of starting the culture, the CO2 requirements of the dissolution tanks 14A to 14C can also be leveled out.

[0083] The microbial culture system 1 of this embodiment further includes a gas flow path control device 20 that can change the order in which the biogas passes through the dissolution tanks 14A-14C. The gas flow path control device 20 changes the order in which the biogas passes through the dissolution tanks 14A-14C so that the biogas first passes through the dissolution tank 14A-14C corresponding to the culture tank 16A-16C in the culture stage with a relatively large CO2 requirement. This makes it possible to both accommodate fluctuations in the CO2 requirement and to homogenize the methane concentration of the biogas after dissolution treatment.

[0084] This allows the order of the dissolution tanks 14A to 14C through which the biogas is aerated to be set so as to correspond to the amount required by the culture tanks 16A to 16C, so that the amount of dissolution in each of the dissolution tanks 14A to 14C is constant, thereby suppressing fluctuations in the gas composition of the biogas after dissolution.High-quality methane gas concentration can be stored in the gas holder 15.

[0085] In addition, in this embodiment, the dissolution liquid supplied to the system (such as the dissolution liquid circulated by the circulation device 40) is seawater, and marine purple photosynthetic bacteria are cultured as anoxygenic photosynthetic microorganisms in the culture tanks 16A to 16C.

[0086] This allows seawater, which is easy to obtain and use in terms of cost, to be used as a dissolution medium or for cultivation. This configuration is more suitable for operating the microbial cultivation system 1 in a location close to the sea. In addition, using seawater rather than freshwater, which has a wider range of uses, is beneficial from the perspective of resource conservation.

[0087] In the above embodiment, the microorganism culture system 1 is configured to include a plurality of dissolution tanks 14A-14C and a plurality of culture tanks 16A-16C, but the number of dissolution tanks and the number of culture tanks are not limited to this configuration. For example, there may be one dissolution tank and one culture tank, or four or more of each.

[0088] In addition, within the scope of the spirit of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modified examples may be combined as appropriate. [Explanation of symbols]

[0089] 1. Microbial culture system 11 Methane fermentation tank 14A~14C Dissolution tank 16A~16C Culture tank 20 Gas flow control device 40 Circulation device

Claims

1. Organic waste is biodegraded by methanogens to produce methane and CO ２ a methane fermenter for producing biogas containing the CO in the biogas produced by the methane fermenter ２ a dissolution tank that dissolves the methane in a dissolution solution to increase the methane concentration in the biogas due to the difference in relative solubility; CO ２ a culture tank for culturing non-oxygenous photosynthetic microorganisms under anaerobic conditions using the solution containing the above-mentioned dissolved therein; CO ２ A circulation device that circulates the dissolution solution in which the above-mentioned is dissolved from the dissolution tank through the culture tank and back to the dissolution tank; A microbial culture system comprising:

2. a plurality of the dissolution tanks are arranged in a flow path of the biogas produced in the methane fermentation tank; The culture tank is arranged in plurality corresponding to the plurality of dissolution tanks, The microbial culture system according to claim 1 , wherein the circulation device independently performs the circulation treatment for each combination of the dissolution tank and the culture tank.

3. The microbial culture system according to claim 2 , wherein the timing at which the culture of the anoxygenic photosynthetic microorganisms is started is different in each of the plurality of culture tanks.

4. The biogas dissolution apparatus further includes a gas flow path control device that can change the order in which the biogas passes through the plurality of dissolution tanks, In the plurality of culture tanks, ２ 4. The microbial culture system according to claim 3, wherein the gas flow path control device changes the order in which the biogas passes through the dissolution tanks so that the biogas passes first through the dissolution tank corresponding to the culture tank in a culture stage with a relatively large required amount.

5. The microbial culture system according to claim 1 , wherein the dissolution solution is water containing 0.5% by mass or more and 4.0% by mass or less of sodium chloride.

6. 5. The microbial culture system according to claim 1, wherein the anoxygenic photosynthetic microorganism is a marine purple photosynthetic bacterium.

7. The microbial culture system according to claim 1 , wherein the culture tank has an airtight structure.

8. 5. The microbial culture system according to claim 1, further comprising a desulfurization device disposed in a flow path of the biogas produced in the methane fermentation tank, for removing hydrogen sulfide contained in the biogas.

Images