Marine acidification inhibition methods

Abstract

To provide a method for suppressing marine acidification that enables safe and stable treatment of carbonate and improves marine environment.SOLUTION: A method for suppressing ocean acidification includes: an injection step in which carbonate is introduced into ocean, and a step of determining a location for retention by which the location for retaining carbonate is determined based on ocean acidity, wherein carbonate is retained at the location determined in the step of determining the location for retaining carbonate. According to this invention, when injecting carbonate into ocean, a location for retaining carbonate is determined based on ocean acidity, and carbonate is supplied (transported) to and retained in that location, effectively promoting the alkaline pump effect. This enables safe and stable treatment (dissolution) of carbonate, and neutralization of seawater in areas of high ocean acidity (suppression of ocean acidification), as well as improvement of the ocean environment by increasing the efficiency of carbon dioxide absorption.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for inhibiting ocean acidification. [Background technology]

[0002] In recent years, reducing carbon dioxide emissions into the environment has become an urgent issue, as it is believed to have a major impact on environmental problems such as global warming. To address this issue, research is being conducted into technologies to reduce carbon dioxide emissions themselves, as well as technologies to capture and fix emitted carbon dioxide.

[0003] In particular, various methods have been investigated for the capture and fixation of carbon dioxide. For example, methods for capturing carbon dioxide from carbon dioxide-containing gases include the chemical absorption method, in which carbon dioxide is dissolved in an absorbing solution such as monoethanolamine, the physical adsorption method, in which carbon dioxide is adsorbed onto an adsorbent with gas adsorption capacity, and the membrane separation method, which uses a membrane. In addition to these methods, from the perspective of reducing the concentration of carbon dioxide in the atmosphere, methods related to ocean storage are being considered, in which carbon dioxide is supplied to the ocean, stored in the ocean, and isolated from the atmosphere.

[0004] For example, Patent Document 1 describes a carbon dioxide fixation system in which deep seawater is pumped up to near the sea surface and carbon dioxide is absorbed into the pumped seawater. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-262888 Summary of the Invention [Problem to be solved by the invention]

[0006] As described in Patent Document 1, when carbon dioxide is directly absorbed into seawater, atmospheric carbon dioxide can be temporarily dissolved in the seawater, but due to the difference in carbon dioxide partial pressure with that of the atmosphere, the carbon dioxide dissolved in the seawater will be released back into the atmosphere. Furthermore, even if carbon dioxide can be effectively dissolved in seawater and the amount of carbon dioxide stored in the ocean increased, the dissolved carbon dioxide in the ocean may cause ocean acidification, which is a decrease in ocean pH.

[0007] Ocean acidification is involved in the growth and reproduction of various marine organisms, raising concerns about its impact on ecosystems. Furthermore, while the ocean naturally absorbs a certain amount of carbon dioxide, ocean acidification reduces the amount of carbon dioxide that the ocean can absorb, potentially contributing to an increase in atmospheric carbon dioxide. Furthermore, as atmospheric carbon dioxide concentrations increase, so does the concentration of carbon dioxide coming into contact with the ocean surface, meaning ocean acidification continues unabated. This raises the risk that the two problems of ocean acidification and increasing atmospheric carbon dioxide concentrations will simultaneously become more serious.

[0008] In addition, a technology for immobilizing carbon dioxide is being considered, which does not involve direct absorption of carbon dioxide by the ocean, but involves introducing carbon dioxide into a solution containing alkaline earth metal ions, thereby producing carbonates through a reaction between the carbon dioxide and the alkaline earth metal ions. The carbonate produced in this process is a stable compound, and carbon dioxide is not easily re-released. However, there are currently few applications for this, and as the technology for carbon dioxide fixation processing is expanded in scale, it will become necessary to address the problem of surplus carbonate.

[0009] An object of the present invention is to provide a method for inhibiting ocean acidification that enables safe and stable treatment of carbonates and also improves the marine environment. [Means for solving the problem]

[0010] As a result of extensive research into the above-mentioned problems, the inventors discovered that by retaining carbonates in specific locations in the ocean, it is possible to treat carbonates and suppress ocean acidification, and thus completed the present invention. That is, the present invention provides the following method for inhibiting ocean acidification.

[0011] The method for inhibiting ocean acidification of the present invention, which solves the above-mentioned problems, comprises an injection step of injecting carbonates into the ocean, and a retention location determination step of determining a location for the carbonates to be retained based on ocean acidity, and is characterized in that the carbonates are retained in the location determined in the retention location determination step. Carbonates are stable compounds, and simply adding them to the ocean does not change the physical properties of seawater. However, it is known that carbonates dissolve when a low-pH aqueous solution is used under pressurized conditions. Here, the ocean becomes pressurized above atmospheric pressure depending on its depth. Furthermore, while the ocean surface has a pH of about 8.1, there are regions where ocean acidity (pH) decreases deeper than the ocean surface. Therefore, if carbonates are retained in regions of low ocean acidity, they will dissolve in those areas, increasing the alkalinity of seawater and promoting the alkaline pump effect, which increases the efficiency of carbon dioxide absorption. According to the method for inhibiting ocean acidification of the present invention, when carbonates are injected into the ocean, a location for retaining the carbonates is determined based on ocean acidity, and the carbonates are supplied (transported) and retained in that location, thereby effectively promoting the alkali pump effect. This makes it possible to safely and stably treat (dissolve) carbonates while simultaneously improving the marine environment by neutralizing seawater in areas with high ocean acidity (inhibiting ocean acidification) and increasing the efficiency of carbon dioxide absorption.

[0012] Furthermore, one embodiment of the method for inhibiting ocean acidification of the present invention is characterized by further comprising a carbonate production step in which the water to be treated, which contains carbon dioxide and alkaline earth metal ions, is concentrated by osmosis using a semipermeable membrane to produce carbonate. According to this feature, carbonates produced in the carbon dioxide fixation process can be used as the carbonates to be injected into the ocean, and since concentration by permeation using a semipermeable membrane is performed in this carbonate production process, it is possible to concentrate the water to be treated and obtain carbonates using less energy than when concentrating the water by heating and evaporating it. Therefore, it is possible to treat surplus carbonates that arise from large-scale carbon dioxide fixation treatment, and to achieve cost and energy savings in obtaining carbonates to be used to suppress ocean acidification.

[0013] Furthermore, one embodiment of the method for inhibiting ocean acidification of the present invention is characterized by further comprising an injection position determination step of determining a position for injecting carbonate based on ocean current predictions. This feature makes it possible to utilize ocean currents to retain carbonates in a predetermined retention location, thereby reducing the cost of constructing a transport route for retaining carbonates in the predetermined retention location and the energy required to transport carbonates, thereby achieving cost and energy savings in carbonate treatment and marine environment improvement. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a method for inhibiting ocean acidification that enables safe and stable treatment of carbonates and also improves the marine environment. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic explanatory diagram showing an example of steps in a method for suppressing ocean acidification according to a first embodiment of the present invention and a system for carrying out each step. [Figure 2] 1 is a graph showing the relationship between ocean acidity and depth, and the relationship between aragonite saturation and depth in a certain ocean area. [Figure 3]FIG. 1 is a schematic explanatory diagram showing an example of a system (carbonate generating apparatus) for carrying out a carbonate generating step in a method for suppressing ocean acidification according to a second embodiment of the present invention. [Figure 4] 1 is a graph showing the abundance ratio of carbonate substances in seawater and freshwater as the pH changes. [Figure 5] FIG. 4 is a schematic explanatory view showing another aspect of the carbonate generating apparatus according to the second embodiment of the present invention. [Figure 6] FIG. 1 is a schematic explanatory diagram showing an example of steps in a method for suppressing ocean acidification according to a third embodiment of the present invention and a system for carrying out each step. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the method for suppressing ocean acidification according to the present invention will be described in detail. Note that the method for suppressing ocean acidification described in the embodiments is merely an example for explaining the method for suppressing ocean acidification according to the present invention, and the present invention is not limited thereto.

[0017] The method for inhibiting ocean acidification of the present invention enables the safe and stable treatment of carbonates and improves the marine environment. More specifically, it enables the treatment of carbonates and the inhibition of ocean acidification by retaining carbonates in specific locations in the ocean.

[0018] [First embodiment] A specific example of the method for suppressing ocean acidification according to the first embodiment of the present invention includes an injection step of injecting carbonates into the ocean and a retention location determination step of determining a retention location for the carbonates based on ocean acidity. The method for suppressing ocean acidification according to this embodiment causes the carbonates to retain in the predetermined location determined in the retention location determination step. FIG. 1 is a schematic explanatory diagram showing an example of each step in the method for suppressing ocean acidification according to the first embodiment of the present invention and a system for carrying out each step.

[0019] The injection step in this embodiment may be any step that can inject carbonate into the ocean, and the specific implementation means and system thereof are not particularly limited. For example, one example of a system for carrying out the injection process of this embodiment is one that includes a floating structure 10 installed on the sea, a storage container 11 for storing carbonates, and an injection section 12 for injecting the carbonates into the ocean, as shown in Figure 1.

[0020] The floating structure 10 may be, for example, a float (mega-float) or a ship, as long as it can maintain a floating state on the sea, and preferably has the function of enabling it to move in a predetermined direction and be moored at a predetermined location. This makes it easy to appropriately change the location where the carbonate is introduced in the introduction step so that the carbonate is retained in a predetermined retention location.

[0021] The storage container 11 may be any container that can be loaded onto the floating structure 10 and that can store carbonates, and it is preferable that the storage container 11 also has the function of maintaining conditions that suppress the deterioration of carbonates.

[0022] Here, examples of carbonates that are stored in the storage container 11 and discharged into the ocean include carbonates obtained as main or by-products in various manufacturing industries, as well as carbonates produced during carbon dioxide fixation treatment. In this embodiment, carbonates composed of alkaline earth metal ions and carbonate ions are preferred, and more specifically, calcium carbonate is particularly preferred. The carbonate may be a compound stored in advance in the storage container 11, or may be a product of a carbon dioxide fixation process that involves reacting carbon dioxide with alkaline earth metal ions and is performed by disposing an apparatus or facility on the floating structure 10. The shape and size of the carbonate are not particularly limited, and may be a powder or a molded body. The shape and size of the carbonate can be appropriately selected in consideration of, for example, prevention of clogging in the pipe 12a of the introduction part 12, ease of storage in the storage container 11, and, as will be described later, the sinking rate in the ocean.

[0023] The injection unit 12 is used to inject the carbonate stored in the storage container 11 into the ocean, and functions as a transport path for the carbonate. More specifically, for example, as shown in Fig. 1, it may be a pipe 12a connected to the storage container 11 and having an opening for releasing the carbonate into the ocean. The material and shape (diameter, total length, etc.) of the pipe 12a are not particularly limited, and may be appropriately selected taking into consideration smooth transport of the carbonate and prevention of deterioration due to seawater, etc. Other examples of the insertion section 12 include a housing that holds carbonates inside and has a structure that allows seawater to flow in and out, and a hanging fixture for this housing, and the entire housing is inserted into the ocean.

[0024] The power supply means for driving each system involved in the deployment process is not particularly limited, but it is preferable to use, for example, power supply equipment that uses renewable energy such as solar, wind, or wave power, or surplus electricity from other facilities. In particular, adopting a power supply means that uses renewable energy that does not emit carbon dioxide when generating electricity has the effect of also promoting the reduction of carbon dioxide emissions. Furthermore, as shown in Figure 1, when the system involved in the deployment process is driven at sea, it is preferable to install a power supply means that uses renewable energy such as solar or wind power on the floating structure 10 to enable continuous operation at sea.

[0025] The method for inhibiting ocean acidification in this embodiment involves injecting carbonate into the ocean through the above-mentioned injection step. However, carbonate (particularly calcium carbonate) is generally a stable compound, and simply injecting carbonate into the ocean will result in the carbonate being deposited on the seabed as is, without changing the physical properties of seawater and without affecting the marine environment.

[0026] On the other hand, carbonate dissolution is not a completely inert reaction; for example, it is known that carbonate dissolution occurs when a low pH aqueous solution is used under pressurized conditions. Because ocean water pressure varies depending on depth, pressure in the ocean is higher than atmospheric pressure vertically below the ocean surface. While the ocean surface has a pH of approximately 8.1, there are regions of lower ocean acidity (pH) below the ocean surface. By storing carbonates in areas of low ocean acidity, the carbonates dissolve in those areas, increasing the alkalinity of seawater and enhancing the carbon dioxide absorption efficiency. This promotes the alkaline pump effect, neutralizing seawater (suppressing ocean acidification) and improving the carbon dioxide absorption efficiency, thereby improving the marine environment. This also enables safe and stable processing of carbonates, particularly for the treatment of large quantities of excess carbonate generated during carbon dioxide fixation.

[0027] The retention location determination step in this embodiment is for determining a location for retaining carbonates based on ocean acidity. As mentioned above, when carbonates are introduced into the ocean, they can be retained in areas with low ocean acidity, thereby dissolving the carbonates and suppressing ocean acidification. Therefore, a specific example of a system for carrying out the retention location determination process in this embodiment is one that is provided with a calculation means 20 that uses the ocean acidity of the ocean surface layer as a standard and selects and determines a location in a lower pH range than the ocean surface layer where carbonate dissolution is progressing as a carbonate retention location.

[0028] This calculation means 20 may include, for example, a means for acquiring and inputting ocean acidity (pH) in the ocean surface and vertically downward (depth) in any region, and a means for determining an area that satisfies the conditions for carbonate dissolution to proceed as a carbonate retention location (point A in Figure 1) from the acquired information on ocean acidity (pH) and outputting it. In this case, the means for acquiring and inputting ocean acidity may involve measuring pH at each depth in any ocean area and directly acquiring information related to ocean acidity, or may involve selecting and acquiring the necessary information from known information related to ocean acidity (such as a database). One example of a means for determining and outputting carbonate retention locations is to set a numerical range of ocean acidity (e.g., pH 8.0 or less) that satisfies the conditions for carbonate dissolution, and select an area that satisfies this set numerical range as a carbonate retention location. Another example is to set the ocean acidity of the ocean surface as a reference value, and select an area where the change or difference from this reference value is within a predetermined range as a carbonate retention location. More specifically, for example, an area where the ocean acidity value is 95% or less of the reference value, or where the difference from the reference value is 0.1 or more, may be selected as a carbonate retention location.

[0029] In addition to ocean acidity, the retention location determination step of this embodiment may also use other parameters related to conditions under which carbonate dissolution progresses, such as depth related to pressurization conditions and carbonate saturation. In particular, the carbonate saturation may be determined by using aragonite saturation or calcite saturation, which are saturations related to calcium carbonate. For example, in regions where the aragonite saturation is lower than in the ocean surface, the dissolution of carbonate (calcium carbonate) is more likely to proceed. Therefore, by determining a retention location using information related to aragonite saturation in addition to information related to ocean acidity in the calculation means 20, it is possible to determine a location that satisfies the conditions for further carbonate dissolution.

[0030] Figure 2 shows a graph showing the relationship between ocean acidity (pH) and depth in a given region (ocean area) (top right of Figure 2) and a graph showing the relationship between aragonite saturation (Ωar) and depth (top left of Figure 2) (Source: Kawai, Zhang, Geochemistry 53, 173-182 (2019)). As shown in Figure 2, the ocean acidity and aragonite saturation values ​​vary depending on the ocean area and depth, so the retention site determination process selects and determines a suitable location for retaining carbonates.

[0031] A specific example of the staying place determining step will be illustrated with reference to FIG. For example, in one ocean area (NP in Figure 2), ocean acidity drops sharply at depths of 500 m or more, and aragonite saturation also drops. Therefore, in the retention location determination process, an area that meets the latitude and longitude of this ocean area (NP) and a depth of 500 m or more can be determined as a carbonate retention location. In another ocean area (CB in Figure 2), there is an area where ocean acidity and aragonite saturation drop near a depth of 200 m. Therefore, the latitude and longitude of this ocean area (CB) and a depth of about 200 m can be determined as a carbonate retention location.

[0032] There are no particular limitations on the specific means for retaining the carbonate in the location (retention location) determined in the retention location determining step. For example, if the determined retention location corresponds to the seabed of the sea area, the floating structure 10 in the injection step can be moored in the sea area (on the ocean) and carbonate can be injected through the injection unit 12 (piping 12a) to cause the carbonate to sink and accumulate toward the retention location (seabed). In this case, the injection step may include a mechanism for increasing the settling speed of the carbonate. For example, the injection unit 12 may be provided with a supply mechanism for high-pressure fluid (air / water (seawater)) to propel the injection (discharge) of the carbonate, or a molding mechanism for molding the carbonate in the storage container 11 into a mass. This makes it possible to more reliably transport the carbonate to the determined retention location, even when the carbonate must sink over a considerable distance. Furthermore, if the determined retention location corresponds to a specific depth range in the sea area, the opening of pipe 12a in injection section 12 can be extended to the specific depth and pulverized carbonate can be injected. This allows the carbonate to diffuse horizontally to a certain extent at the injected depth, making it possible to keep the carbonate within the specific depth range. Furthermore, instead of pipe 12a, injection section 12 can be configured to use a housing that holds carbonate inside and has a structure that allows seawater to enter and exit, and a hanging fixture for this housing, and moor the housing within the specific depth range.

[0033] As described above, the method for inhibiting ocean acidification in this embodiment involves injecting carbonate into the ocean, determining a location for retaining the carbonate based on ocean acidity, and supplying (transporting) and retaining the carbonate at that location, thereby effectively promoting the alkali pump effect. This makes it possible to safely and stably treat (dissolve) carbonate while simultaneously improving the marine environment by neutralizing seawater in areas with high ocean acidity (inhibiting ocean acidification) and increasing the efficiency of carbon dioxide absorption.

[0034] [Second embodiment] The method for inhibiting ocean acidification according to the second embodiment of the present invention includes, in addition to the steps of the method for inhibiting ocean acidification according to the first embodiment, a carbonate production step in which water to be treated containing carbon dioxide and alkaline earth metal ions is concentrated by permeation using a semipermeable membrane to produce carbonate. Note that the same components as those in the first embodiment will not be described or illustrated.

[0035] The carbonate production step in this embodiment produces carbonate in association with the carbon dioxide fixation treatment, and furthermore, by performing concentration by permeation using a semipermeable membrane, concentration can be performed with less energy than concentration by thermal evaporation, which enables cost and energy savings in obtaining carbonate to be injected into the ocean in the injection step.

[0036] The carbonate production step in this embodiment uses a semipermeable membrane that allows water molecules to pass through but does not or has poor permeability to the ions necessary for carbonate production. By using such a semipermeable membrane to concentrate the water to be treated, which contains carbon dioxide and alkaline earth metal ions, the concentration of water molecules is reduced while the carbonate ions present in the water to be treated are prevented or made poorly permeable, thereby increasing the carbonate ion concentration in the concentrate. This causes the carbonate ions to react with the alkaline earth metal ions to produce alkaline earth metal carbonates. Furthermore, when water to be treated having a pH exceeding 7 is concentrated using a semipermeable membrane, the concentrate obtained by the semipermeable membrane has a reduced number of water molecules and an increased concentration of hydroxide ions. Therefore, the increased pH of the concentrate facilitates the production of carbonate ions, which has the effect of facilitating the production of alkaline earth metal carbonates.

[0037] Here, to explain why an increase in the pH of the concentrated liquid makes it easier for carbonate ions to be produced, in carbonated water with dissolved carbon dioxide, a chemical equilibrium equation such as that shown in Equation 1 generally holds.

number

[0038] As shown in Equation 1, in carbonated water, some of the carbonic acid (H2CO3) is converted into hydrogen ions (H + ) and bicarbonate ions (HCO3 - ) and hydrogen ions are further ionized from the bicarbonate ions to form carbonate ions (CO3 2- ) occurs.

[0039] Here, carbon dioxide (H2CO3) and bicarbonate ions (HCO3 - ) to carbonate ions (CO3 2- To increase the ratio of carbonate ions (CO3 2- It is known that the abundance ratio of

[0040] In the carbonate generation process of this embodiment, the above phenomenon is utilized, and the water to be treated having a pH of more than 7 is concentrated to increase the pH, thereby generating carbonate ions (CO 2- ) can be more efficiently produced carbonates of alkaline earth metals.

[0041] Furthermore, the carbonate production process in this embodiment uses a semipermeable membrane as described above to concentrate the water to be treated, and as a result, the water to be treated can be concentrated and carbonate obtained using less energy than in the conventional method of concentrating water to be treated, such as seawater, by evaporating it (such as a method called simple distillation). Specifically, when trying to evaporate and concentrate the water in seawater to be treated and obtain carbonates, the energy required to evaporate the water is approximately 626 kWh / m. 3 In contrast, the energy required to produce pure water from seawater using a semipermeable membrane is approximately 0.69 kWh / m 3 is.

[0042] In the carbonate production step of this embodiment, it is preferable to introduce salt-containing water to be treated into the concentrated side and a salt-containing liquid into the dilution side. The salt concentration of the liquid on the dilution side is preferably the same as that of the water to be treated on the concentrated side, and more preferably the salt concentration of the liquid on the dilution side is higher than that of the water to be treated on the concentrated side. By containing salt in the liquid on the dilution side, the difference in salt concentration between the water to be treated on the concentration side and the liquid on the dilution side becomes smaller, allowing the water to be concentrated with less energy and carbon dioxide fixation treatment to be carried out.Furthermore, by making the salt concentration of the liquid on the dilution side higher than the salt concentration of the water to be treated on the concentration side, osmotic pressure (forward osmosis) is generated, allowing the water to be treated on the concentration side to be concentrated with less energy.

[0043] FIG. 3 is a schematic explanatory diagram showing an example of a system for carrying out the carbonate production step in the method for suppressing ocean acidification according to the second embodiment of the present invention. Hereinafter, with reference to FIG. 3, a specific example of a system for carrying out the carbonate production step in this embodiment (hereinafter referred to as a "carbonate production device") will be described. The carbonate production apparatus 100 of this embodiment has a concentration section 110, which produces carbonate by concentrating the water to be treated W. The carbonate production apparatus 100 of this embodiment may be disposed on the floating structure 10 in the input step, or may be disposed on land so that the produced carbonate can be collected and transported to a system that performs the input step.

[0044] [Untreated water] The water to be treated W is an aqueous solution containing carbon dioxide and alkaline earth metal ions, and is not particularly limited as long as the concentration of carbonate ions (carbon dioxide) increases and alkaline earth metal carbonates are more likely to be produced when the water to be treated W is concentrated by the semipermeable membrane 130. The increased concentration of carbonate ions has the effect of reacting with the alkaline earth metal ions and more likely to produce alkaline earth metal carbonates. The carbon dioxide contained in the water to be treated W is a mixture of carbon dioxide (H2CO3) in the aqueous solution and bicarbonate ions (HCO3 - ) and carbonate ions (CO3 2- ) and gaseous carbon dioxide (CO2) dissolved in an aqueous solution. - ) and carbonate ions (CO3 2- ) are referred to as carbonate substances, and carbon dioxide (CO2) in gaseous form dissolved in an aqueous solution is referred to as carbon dioxide gas. In addition, in Figure 3, calcium ions (Ca 2+ ) is shown as an example.

[0045] The water to be treated W that can be used in this embodiment is not particularly limited in terms of its origin, as long as it is an aqueous solution containing carbon dioxide and alkaline earth metal ions. It may be water in which carbon dioxide has been artificially dissolved, or in which a substance that becomes alkaline earth metal ions has been artificially dissolved, or an aqueous solution in which carbon dioxide and alkaline earth metal ions have been dissolved from the beginning may be used. Specific examples of the water to be treated W include seawater, river water, tap water, pure water, wastewater or effluent from factories, and leachate from landfills.

[0046] The water to be treated W is preferably an aqueous solution containing carbon dioxide and alkaline earth metal ions and having a pH of more than 7.0. The pH of the water to be treated W is preferably 7.5 or higher, and more preferably 8.0 or higher. If the pH of the water to be treated W exceeds 7, when the water to be treated W is concentrated, water molecules pass through the semipermeable membrane 130 and decrease in number, while hydroxide ions do not pass through and their concentration increases, which has the effect of increasing the pH of the concentrated water to be treated W and making it easier for carbonate ions to be produced.

[0047] Furthermore, the water to be treated W is preferably an aqueous solution containing other salts other than salts of carbonate ions and salts of alkaline earth metal ions. An example of the water to be treated W containing other salts is seawater. Figure 4 is a graph showing the abundance ratio of carbonate substances in seawater and freshwater that does not contain other salts as the pH changes. Figure 4 shows that in seawater, carbonate ions begin to be generated at a pH of approximately 6.5, while in freshwater that does not contain other salts, carbonate ions begin to be generated at a pH of approximately 8. In other words, when the pH of an aqueous solution containing other salts is the same as the pH of an aqueous solution not containing other salts, the aqueous solution containing other salts is more likely to produce more carbonate ions, so when the water to be treated W contains other salts, carbonate ions can be produced efficiently without increasing the pH. As for the tendency related to the pH at which carbonate ions begin to be generated, the greater the content of other salts, the lower the pH at which carbonate ions begin to be generated.

[0048] For these reasons, the water to be treated W is preferably an aqueous solution containing carbon dioxide and alkaline earth metal ions, having a pH of 8.0 or higher, and containing other salts. Specifically, seawater is preferred.

[0049] [Concentration section] The carbonate generating apparatus 100 in this embodiment includes a concentration section 110 , which includes a treatment tank 120 , a semipermeable membrane 130 , and a pressurizing means 140 .

[0050] [Treatment tank] The treatment tank 120 is not particularly limited in terms of material, shape, or size as long as it is capable of storing the water to be treated W. The treatment tank 120 is divided into a first chamber 120a and a second chamber 120b, which are separated by a semipermeable membrane 130 described below. The water to be treated W is supplied to each of the first chamber 120a and the second chamber 120b. The water to be treated W in the first chamber 120a and the water to be treated W in the second chamber 120b are not mixed with each other.

[0051] [Semi-permeable membrane] The semipermeable membrane 130 is a membrane that allows water molecules of the water to be treated W to pass through but does not allow ions necessary for carbonate production, including carbonate ions and alkaline earth metal ions contained in the water to be treated W, to pass through, or a membrane that does not allow ions necessary for carbonate production to pass through easily. The reason why the semipermeable membrane 130 in this embodiment allows water molecules to pass through but does not or does not easily allow ions necessary for carbonate generation contained in the water to be treated W to pass through is that ions in the aqueous solution undergo a phenomenon called hydration, and the ions in the aqueous solution interact with the water molecules. Therefore, ions in the hydrated state are larger than single water molecules that are not hydrated. Here, the semipermeable membrane 130 has pores large enough to allow unhydrated water molecules to pass through, but large enough to prevent hydrated ions from passing through. Therefore, even if hydrated ions attempt to pass through the semipermeable membrane 130 together with the interacting water molecules, they are unable to do so. On the other hand, unhydrated water molecules are able to pass through the semipermeable membrane 130. For the above reasons, the semipermeable membrane 130 exhibits the function of allowing water molecules of the water to be treated W to pass through, while preventing or limiting the permeation of ions necessary for carbonate production contained in the water to be treated W.

[0052] Furthermore, the semipermeable membrane 130 is preferably permeable to carbon dioxide gas. When the semipermeable membrane 130 allows carbon dioxide gas to pass through, the concentration of gaseous carbon dioxide does not increase on the side of the concentrated liquid 150 obtained by concentrating the water to be treated W. Therefore, the gaseous carbon dioxide becomes a carbonate substance, which can prevent a decrease in the pH of the concentrated liquid and create a state in which carbonate ions are easily generated. In particular, when water to be treated W having a pH exceeding 7 is used, the synergistic effect of the effect of increasing the pH due to the increase in the hydroxide ion concentration and the effect of suppressing the increase in the carbon dioxide concentration makes it easier to generate carbonate ions.

[0053] [Pressure means] The pressurizing means 140 is not particularly limited as long as it is a means for applying pressure to the water to be treated W in the first chamber 120a and the semipermeable membrane 130. An example of the pressurizing means 140 is one that applies pressure to the water to be treated W by an external force, such as a method in which a pump that sends air is connected to the first chamber 120a and the air is sent in a sealed state to apply pressure. The pressurizing means 140 applies pressure to the water W in the first chamber 120a and the semipermeable membrane 130, causing water molecules to permeate from the first chamber 120a to the second chamber 120b, concentrating the water W in the first chamber 120a. The water W in the first chamber 120a becomes a concentrated liquid 150, and the water W in the second chamber 120b becomes a diluted liquid 160.

[0054] [Carbonate generator operation] The operation of the carbonate production device 100 in the carbonate production step will be described with reference to Figure 3. In the following description, the case will be described in which water to be treated W having a pH exceeding 7.0 is used, and the semipermeable membrane 130 is a membrane that is permeable to water molecules and carbon dioxide gas in the water to be treated W, but is impermeable or has poor permeability to ions necessary for carbonate production. First, as shown in the upper diagram of Fig. 3, the water to be treated W is supplied to the treatment tank 120 (first chamber 120a and second chamber 120b). This step is referred to as the water to be treated supply step. The first chamber 120a and the second chamber 120b have the same shape, and the same amount of water to be treated W is supplied to each chamber, so that the water level of the water to be treated W in the first chamber 120a and the water level of the water to be treated W in the second chamber 120b are set to the same level.

[0055] Next, the water W to be treated in the first chamber 120a is pressurized by the pressurizing means 140. This step is referred to as the pressurizing step.

[0056] Next, as shown in the lower diagram of FIG. 3, the water W to be treated in the first chamber 120a is pressurized, causing water molecules and carbon dioxide gas in the water W to pass through the semipermeable membrane 130 and move toward the second chamber 120b. At this time, hydroxide ions, bicarbonate ions, carbonate ions, and alkaline earth metal ions (calcium ions) contained in the water to be treated W do not move from the first chamber 120a to the second chamber 120b. Ions that do not pass through the semipermeable membrane 130 or that are difficult to pass through, such as hydroxide ions, bicarbonate ions, carbonate ions, and alkaline earth metal ions, are hereinafter referred to as impermeable ions. Therefore, the non-permeating ions remain in the first chamber 120a, and the volume of the original water to be treated W decreases, resulting in a concentrated state. This concentrated state of the water to be treated W in the first chamber 120a is the concentrated liquid 150. The process of producing the concentrate 150 from the water to be treated W by the concentrating section 110 is referred to as a concentration step in which the water to be treated is concentrated to produce the concentrate.

[0057] On the other hand, the impermeable ions of the water W to be treated in the second chamber 120b do not move from the second chamber 120b to the first chamber 120a. Therefore, the water W to be treated in the second chamber 120b becomes diluted as the volume of the original water W increases due to the permeation of water molecules and carbon dioxide gas from the first chamber 120a. This diluted state of the water W to be treated in the second chamber 120b is the dilution liquid 160. The process of producing the diluent 160 from the water to be treated W by the concentrating section 110 is referred to as a dilution step in which the water to be treated is diluted to produce the diluent.

[0058] Here, the concentrated liquid 150 is concentrated from the state of the water to be treated W, and the pH increases as a result of a decrease in water molecules and carbon dioxide gas. Therefore, the concentration of carbonate ions in the concentrated liquid 150 increases, and carbonate salts are generated by reaction with alkaline earth metal ions. The above-mentioned operation results in the production of carbonates accompanying the fixation of carbon dioxide. The produced carbonates are recovered and used as carbonates in the charging step.

[0059] In the above description of the operation of the carbonate generation device 100, the treated water W having a pH exceeding 7.0 is used, and the semipermeable membrane 130 is a membrane that allows water molecules and carbon dioxide gas in the treated water W to pass through, but does not allow or has poor permeability to ions necessary for carbonate generation.However, the carbonate generation device 100 that performs the carbonate generation process in this embodiment is not limited to cases where the treated water W has a pH exceeding 7. For example, if the water to be treated W contains other salts, has a pH of 7 or higher, and contains carbonate ions, the semipermeable membrane 130 may be a membrane that is permeable to water molecules, carbon dioxide gas, and hydrogen ions, but is impermeable to or has poor permeability to other ions necessary for carbonate production, excluding hydrogen ions. This prevents hydrogen ions from concentrating in the concentrated liquid 150, thereby preventing a decrease in pH and increasing the concentration of carbonate ions, facilitating the production of alkaline earth metal carbonates.

[0060] Furthermore, in the carbonate generation apparatus 100 of this embodiment, the same water to be treated W is used in the first chamber 120a and the second chamber 120b, and the concentrated liquid 150 and the diluted liquid 160 are generated by the pressurizing means 140, but this is not limited to this. FIG. 5 is a schematic explanatory diagram showing another aspect of the carbonate generating device in this embodiment. 5, the first chamber 120a and the second chamber 120b may be formed to have the same shape, with the water to be treated W being introduced into the first chamber 120a, and high-concentration water to be treated 170 having a higher salt concentration than the water to be treated W in the first chamber 120a being introduced into the second chamber 120b in the same amount as the water to be treated W in the first chamber 120a. The water level in the first chamber 120a and the water level in the second chamber 120b are the same height. 5, since the salt concentration in the second chamber 120b is higher than that in the first chamber 120a, the water molecules of the water to be treated W in the first chamber 120a permeate into the second chamber 120b (forward osmosis) due to osmotic pressure, and the water to be treated W in the first chamber 120a is concentrated to become a concentrated liquid 150. In addition, the high-concentration water to be treated 170 in the second chamber 120b is diluted to become a diluted liquid 160. As shown in Fig. 5, when there is a difference in concentration between the water to be treated W in the first chamber 120a and the high-concentration water to be treated 170 in the second chamber 120b that is sufficient to generate osmotic pressure (forward osmosis), concentration is performed by osmotic pressure (forward osmosis), and therefore concentration can be performed without using the pressurizing means 140. Note that the pressurizing means 140 may also be used in the carbonate production apparatus shown in Fig. 5. In this case, because osmotic pressure (forward osmosis) is generated, the pressure by the pressurizing means 140 can be reduced, and the concentrated liquid 150 and the diluted liquid 160 can be produced with less energy.

[0061] As described above, in the method for suppressing ocean acidification in this embodiment, carbonates produced in the course of carbon dioxide fixation treatment can be used as the carbonates to be injected into the ocean. Furthermore, in this carbonate production step, concentration by permeation using a semipermeable membrane is performed, so that the water to be treated can be concentrated and carbonates obtained using less energy than when the water to be treated is concentrated by heating and evaporating it. Therefore, it is possible to treat surplus carbonates that accompany large-scale carbon dioxide fixation treatment, and it is also possible to achieve cost and energy savings in obtaining carbonates to be used for suppressing ocean acidification.

[0062] [Third embodiment] The method for mitigating ocean acidification according to the third embodiment of the present invention includes, in addition to the steps of the method for mitigating ocean acidification according to the first embodiment, an injection position determination step of determining a position for injecting carbonate based on ocean current prediction. Note that the same components as those in the first embodiment will not be described or illustrated.

[0063] In the injection position determination step of this embodiment, when injecting carbonate into the ocean, the injection position of the carbonate is determined in advance based on ocean current prediction, which makes it possible to use ocean currents as a means for transporting the carbonate to a retention location, thereby making it possible to significantly reduce the energy and initial costs required to transport the carbonate to a predetermined location (retention location).

[0064] FIG. 6 is a schematic explanatory diagram showing an example of each step in the method for suppressing ocean acidification according to the third embodiment of the present invention and a system for carrying out each step. The injection location determination process in this embodiment uses ocean current predictions to determine the location for injecting carbonate into the ocean, and this injection location is a location where the carbonate can be transported to a retention location using ocean currents. A specific example of a system that performs the injection position determination process in this embodiment is one that includes a calculation means 30 that acquires information related to ocean current predictions, compares this with information related to the retention location determined in the retention location determination process, and selects and determines an appropriate carbonate injection position for transporting the carbonate to the retention location by ocean currents.

[0065] The calculation means 30 may be integrated with the calculation means 20 described above, or may be provided separately. The calculation means 30 may include, for example, a means for acquiring and inputting information related to ocean current prediction, a means for acquiring and inputting information (latitude, longitude, and depth) related to the retention location (point A) determined in the retention location determination process, and a means for regarding the information related to the retention location as the destination point and the information related to the ocean current prediction as the route, selecting and determining an appropriate starting point based on the destination point and the route, and outputting the carbonate injection position (latitude, longitude). The information related to ocean current prediction may use actual measurements or past measurements of the speed and direction of ocean currents, or may use calculated values ​​obtained through simulations using topography and seawater temperature.

[0066] Here, the location selected and determined as the starting point (carbonate injection location) may be on the sea or on land. When the carbonate injection location is on land, map information of the land (coastal area), such as a topographical map or a city block map, may be used as one of the factors for determining whether the starting point is appropriate, and the ease of work, such as securing a work location for the carbonate injection process, may be taken into consideration.

[0067] Furthermore, as the charging step in this embodiment, when the carbonate charging position is on the sea, the system for the charging step shown in the first embodiment can be used, but when the carbonate charging position is on land, a carbonate storage container 11 and a charging unit 12 can be provided on land as shown in Fig. 6. In this case, the storage container 11 and the charging unit 12 may be fixed at a specific location on land, or may have a function to be movable according to the carbonate charging position determined in the charging position determination step.

[0068] The method for inhibiting ocean acidification in this embodiment transports carbonates using ocean currents. Therefore, regardless of the carbonate injection location, the injection section 12 in the injection step in this embodiment only needs to be capable of injecting carbonates into the ocean, and there is no need to provide the injection section 12 with a function for allowing it to reach a retention location, or to design the injection section 12 itself to be long enough to reach the retention location. This makes it possible to significantly reduce the initial cost and energy consumption associated with the injection step.

[0069] As described above, the method for suppressing ocean acidification in this embodiment makes it possible to utilize ocean currents to retain carbonates in a predetermined retention location, thereby reducing the cost of constructing a transport route for retaining carbonates in the predetermined retention location and the energy required to transport carbonates, thereby achieving cost and energy savings in carbonate treatment and marine environment improvement. Furthermore, the method for inhibiting ocean acidification in this embodiment may further include the carbonate production step described in the second embodiment, which also makes it possible to reduce the cost of obtaining carbonate.

[0070] The above-described embodiment shows an example of a method for suppressing ocean acidification. The method for suppressing ocean acidification according to the present invention is not limited to the above-described embodiment, and the method for suppressing ocean acidification according to the above-described embodiment may be modified within the scope of the gist of the claims.

[0071] For example, the carbonate production step in this embodiment may be carried out in multiple steps. In addition, the concentrate introduced into the concentration section in the carbonate production step may be water to be treated that has been supplied to a reverse osmosis device or a forward osmosis device and treated therein.

[0072] Furthermore, instead of the carbonate generation step in this embodiment, a known technique for generating carbonate may be used, such as a technique for immobilizing carbon dioxide by electrolysis, which involves alkalizing a solution. [Industrial Applicability]

[0073] The method for suppressing ocean acidification of the present invention can be suitably used for improving the marine environment and for treating carbonates, particularly for treating excess carbonates produced by carbon dioxide fixation treatment. [Explanation of symbols]

[0074] 10 floating structure, 11 storage container, 12 input section, 12a piping, 20, 30 calculation means, 100 carbonate generation device, 110 concentration section, 120 treatment tank, 120a first chamber, 120b second chamber, 130 semipermeable membrane, 140 pressurization means, 150 concentrated liquid, 160 diluted liquid, 170 high-concentration treated water, point A (carbonate retention location), W treated water

Claims

1. an injection step of injecting carbonate into the ocean; An acquisition step of acquiring ocean acidity in a given region; and a retention location determination step of determining a retention location of carbonates based on the ocean acidity obtained in the obtaining step, A method for inhibiting ocean acidification, characterized in that carbonates are retained in the location determined in the retention location determination step.

2. 2. The method for inhibiting ocean acidification according to claim 1, further comprising a carbonate production step of concentrating the water to be treated, which contains carbon dioxide and alkaline earth metal ions, by permeation using a semipermeable membrane to produce carbonates.

3. 3. The method for suppressing ocean acidification according to claim 1, further comprising an injection position determination step of determining a position for injecting carbonate based on ocean current prediction.

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