Nutrient salt-eluting block and method for producing same

Abstract

Provided is a method for producing a block that can elute nutrient salts, the block being produced by mixing a cement material and a phosphorus compound that is a phosphate that can elute phosphorus in the form of phosphoric acid, and the method comprising: a step for adjusting the content of a low-alkali cement additive, to be added to the cement material, such that the pH of an immersion liquid for the block will become lower than that of Portland cement; and adjusting the content of the phosphorus compound. As a result, recycled resources can be utilized in the production of a block that can elute nutrient salts, and an appropriate elution rate of nutrient salts from the produced block can be maintained.

Description

Nutrient Salt Dissolution Block and Method for Producing the Same

[0001] The present disclosure relates to a nutrient salt dissolution block and a method for producing the same.

[0002] The impact of global warming caused by carbon dioxide and the like emitted along with socio-economic activities has become significant, and efforts towards decarbonization to mitigate this are being considered. Energy-saving technologies for reducing carbon dioxide emissions from power generation and renewable energy technologies such as solar and wind power have been developed and are entering the stage of social implementation. Furthermore, as a carbon-negative technology for advancing decarbonization, the development of DAC technology for directly recovering carbon dioxide from the atmosphere is also underway. Here, DAC is an abbreviation for Direct Air Capture.

[0003] In DAC technology, industrial-based technologies using absorbents and the like are leading the way, but in parallel, studies on DAC using natural-based technologies, namely green carbon which is DAC in forests and blue carbon which is DAC in marine ecosystems, are also being advanced. These natural-based technologies are highly anticipated because they may relatively keep costs low and can secondarily improve the environment other than global warming.

[0004] In particular, blue carbon is a technology area that has been accelerating in recent years because it has advantages such as a larger potential carbon dioxide recovery amount and a longer carbon dioxide fixation period compared to green carbon. It has been scientifically clarified that carbon dioxide recovery in blue carbon is carried out in marine ecosystems such as seaweed and algae beds, mangrove forests, saline wetlands, and phytoplankton breeding areas, and various findings have been accumulated.

[0005] Carbon capture through blue carbon is quantified through ocean monitoring and ultimately converted into carbon offset credits, which are traded on the carbon emissions market. This ocean monitoring typically involves assessing the area of ​​seaweed beds and mangrove forests using methods such as underwater measurements and satellite remote sensing. Assuming this area is proportional to carbon dioxide absorption, carbon offsets are assigned based on the amount of area maintained or expanded.

[0006] The area of ​​seagrass beds and mangrove forests in the target marine area is affected by several factors, but the main factors are known to be nutrients necessary for the proliferation of seagrasses, seaweed, and mangroves, namely nitrogen and phosphorus. Therefore, carbon offsets from seagrass beds and mangrove forests maintained and expanded through appropriate nutrient management in the target marine area will be credited to the implementing body for nutrient management policies.

[0007] Several sources of nutrients exist in the coastal watersheds of the target sea area, with sewage treatment plants and wastewater treatment facilities being the main sources. If carbon offsetting is provided through measures to appropriately manage the amount of nutrients supplied to the sea area to which the discharged water reaches, it will provide an incentive for the operators of sewage treatment plants and wastewater treatment facilities to optimize the treated water quality in terms of nitrogen and phosphorus, and it is expected that efforts to contribute to decarbonization will become even more active.

[0008] Furthermore, means of supplying nutrients to the sea area are not limited to the effluent from sewage treatment plants as described above, but also include methods using equipment and materials that can prioritize supply to the necessary locations.

[0009] For example, Patent Document 1 discloses a sustained-release member capable of sustainably releasing iron ions in seawater or water, comprising at least a first layer containing an iron-containing component and a second layer laminated on the surface of the first layer containing a chelating agent, wherein in seawater or water, iron ions are generated from the first layer, and the iron ions combine with the chelating agent to form a divalent iron complex, and the divalent iron ions are released from the sustained-release member, and the first layer and / or the second layer further contain one or more nutrients selected from the group consisting of nitrogen-containing components, phosphorus-containing components and silicon-containing components.

[0010] Furthermore, Patent Document 2 discloses a nutrient supply material containing methane fermentation digestate or its concentrate obtained from a livestock methane fermentation facility, and seashells such as oyster shells, wherein the nutrients include at least one selected from the group consisting of nitrogen (N), phosphorus (P), and silicon (Si), and the elution of nutrients is controlled.

[0011] Patent Document 3 discloses concrete to which nutrients from algae and plants are added, wherein the nutrients are added to a polymer compound and mixed into the concrete, and the polymer compound is a polyion complex, which is a polymer electrolyte aggregate formed by mixing aqueous solutions of two types of polymers (polyanions and polycations), and the nutrients are adsorbed onto it.

[0012] Japanese Patent Publication No. 2022-149442, Japanese Patent Publication No. 2023-176981, Japanese Patent Publication No. 2024-61188

[0013] Nutrients originating from effluent from sewage treatment plants and other sources are advected and diffused in the sea area where they are discharged, contributing to an overall improvement in nutrient concentration levels in the sea. In this case, however, it is difficult to preferentially and selectively supply nutrients to areas where they are more needed, such as seaweed beds or aquaculture farms.

[0014] Furthermore, the nutrient concentration in wastewater discharged from sewage treatment plants fluctuates depending on the quantity and quality of sewage flowing into the treatment plant at any given time, as well as seasonal fluctuations in water temperature and the activity level of sewage treatment microorganisms (activated sludge). As a result, there are cases where it is difficult to supply the necessary and sufficient amount of nutrients for the growth of marine ecosystems without excess or deficiency.

[0015] The technology disclosed in Patent Document 1 has the advantage of providing long-lasting fertilization effects and being easy to recover after use. The technology disclosed in Patent Document 2 has the advantage of effectively utilizing methane fermentation digestate and seashells, which are currently discarded without being used.

[0016] However, for large-scale applications aimed at absorbing and storing carbon dioxide using blue carbon, it is desirable to obtain both of the advantages described in Patent Documents 1 and 2.

[0017] The inventors have been investigating ways to simultaneously achieve long-term sustained fertilization effects and sustainable use of recycled resources, and are developing a block that utilizes recycled resources while also providing pinpoint, long-term supply of nutrients to the areas where they are needed. To date, they have obtained a sustained-release material (block) that utilizes recycled phosphorus compounds recovered from sewage treatment processes. This material has the practical advantage of maintaining a predetermined strength even when nutrient additives (recycled phosphorus compounds) are added to the base raw material (in this case, cement).

[0018] However, depending on the type and conditions of the regenerated phosphorus compound added, this equipment may not yield the required amount of phosphorus elution. In particular, the elution of magnesium ammonium phosphate (MAP), an example of a regenerated phosphorus compound, is pH-dependent, with a lower elution rate in alkaline conditions.

[0019] Portland cement, the most widely used main material for equipment and materials, is produced by the hydration reaction of calcium hydroxide Ca(OH) ２Because the formation process makes the interpore water in the block strongly alkaline, a practical challenge is that the MAP elution rate becomes lower than the required value.

[0020] The technology disclosed in Patent Document 3 does not utilize recycled resources, nor does it relate to the pH dependence of nutrient elution rates.

[0021] The purpose of this disclosure is to utilize recycled resources in the manufacture of blocks from which nutrients can be leached, and to maintain an appropriate nutrient leaching rate in the manufactured blocks.

[0022] The present disclosure is a method for producing a nutrient-eluting block, comprising mixing a cement material with a phosphorus compound which is a phosphate capable of eluting phosphated phosphorus, to produce a block capable of eluting nutrient salts, the method comprising the steps of adjusting the content of a low-alkalization cement additive added to the cement material so that the pH of the block immersion solution is lower than that of Portland cement, and adjusting the content of the phosphorus compound.

[0023] According to this disclosure, recycled resources can be utilized in the manufacture of blocks from which nutrients can be leached, and an appropriate leaching rate of nutrients in the manufactured blocks can be maintained.

[0024] This figure shows a method for producing nutrient-eluting blocks in a block manufacturing facility according to the embodiment. This is a flow chart showing the details of the low-alkalinization cement material adjustment process S200 in Figure 1. This is a graph showing the relationship between the mixing ratio of cement materials and the pH of the block pore water. This is a flow chart showing the details of the phosphorus compound adjustment process S300 in Figure 1. This is a flow chart showing the details of the block manufacturing process S400 in Figure 1.

[0025] This disclosure relates to a technology for the direct capture of atmospheric carbon dioxide from the air for decarbonization, specifically focusing on blue carbon, which is carbon dioxide capture by marine ecosystems, and concerns the manufacturing technology for materials and equipment that can supply nutrients that contribute to the maintenance and expansion of marine ecosystems such as seaweed beds, which are the main components of this capture effect.

[0026] The embodiments will be described below with reference to the drawings. This embodiment describes an example of a method for producing a nutrient-eluting block using phosphorus compounds.

[0027] Figure 1 shows a method for producing nutrient-eluting blocks in a block manufacturing facility according to an embodiment.

[0028] In this figure, the block manufacturing facility 100 manufactures nutrient-eluting blocks 20 using cement material 1, which is the main material of the block, and phosphorus compound 5, through three steps: a low-alkalinity cement material preparation step S200, a phosphorus compound preparation step S300, and a block manufacturing step S400.

[0029] Here, cement material 1 includes Portland cement. The low-alkali cement material includes cement material 1 and a low-alkali cement additive.

[0030] Furthermore, as phosphorus compound 5, for example, magnesium ammonium phosphate (MAP), a phosphate fertilizer recovered from sewage sludge and wastewater sludge through crystallization treatment, can be used. MAP is a type of phosphate salt that can elute phosphate phosphorus. Since Japan relies almost 100% on imports for phosphorus resources used as industrial raw materials and fertilizers, deliberately utilizing phosphorus recovered from waste is important not only because it contributes to resource recycling but also because it can mitigate competition for the use of valuable phosphorus resources.

[0031] The following describes each step in Figure 1.

[0032] Figure 2 is a flowchart showing the details of the low-alkali cement material preparation process S200 in Figure 1.

[0033] The low-alkali cement material preparation process S200 prepares the block material so that it can be used in the subsequent block manufacturing process S400 (Figure 1).

[0034] In Figure 2, in the initial block material selection step S210, a low-alkalization cement additive is selected that results in a block pore water pH that satisfies the required amount of phosphorus compounds supplied to seawater, i.e., the elution rate, according to the intended use of the nutrient-eluting block 20. Here, pH is the hydrogen ion concentration.

[0035] In the block material delivery process S220, block materials are delivered to the block manufacturing facility 100. The block materials are materials mixed as constituent elements of the block and include at least cement material 1, phosphorus compound 5, and aggregate. Typically, sand or gravel is used as aggregate. In addition to these materials, other materials may be added depending on the purpose and application. For example, as usable waste, water treatment soil, which is residue generated during water treatment at a water treatment facility (not shown), can be used. Water treatment soil is a mixture of turbidity components (mainly silicon) and coagulant components (such as aluminum hydroxide) in raw tap water, and by using it appropriately in a mixing ratio that keeps the mechanical strength of the manufactured block within an acceptable range, it is possible to reduce the amount of cement used.

[0036] In the next block material particle size adjustment step S230, the material is processed to achieve a particle size that does not impair the material's mixability or the uniformity of the block's material. Specifically, this is done by crushing or sieving. If the material has already been particle-sized at the time of the block material delivery step S220, this step can be omitted.

[0037] Then, in the block material weighing process S240, the weight or volume of each material is measured for subsequent processes. Note that if there is equipment that can supply each material in a specified amount in the subsequent block manufacturing process S400 (Figure 1), this process can be omitted.

[0038] The above is an explanation of the flow example for the low-alkalinity cement material adjustment process S200.

[0039] Figure 3 is a graph showing the relationship between the mixing ratio of cement materials and the pH of the pore water between blocks.

[0040] In this figure, it shows an example of data for reference in the block material selection step S210 of FIG. 2 regarding the pH characteristics of the block interstitial water for each low-alkalinity cement material. By preparing such data in advance and referring to it, the selection of the block material can be appropriately carried out. Note that the pH of the block interstitial water is also called "immersion liquid pH".

[0041] The curve in FIG. 3 shows three types of cement materials. The solid line represents the reference Portland cement, the dashed line represents the low-alkalinity cement A, and the dash-dotted line represents the low-alkalinity cement B.

[0042] As shown in FIG. 3, the low-alkalinity cement A has a lower pH of the block interstitial water compared to Portland cement. This is because Portland cement does not contain a low-alkalinity cement additive. Also, the low-alkalinity cement B has a lower pH of the block interstitial water compared to the low-alkalinity cement A. This is because the low-alkalinity cement B has a higher content rate of the low-alkalinity cement additive compared to the low-alkalinity cement A.

[0043] As described above, since MAP, a typical phosphorus compound, shows a high elution rate on the acidic side, the upper pH limit value α for a predetermined MAP elution rate is set by a prior elution test or the like.

[0044] Also, as another constraint condition for selecting the low-alkalinity cement additive, a lower limit value β of the cement material blending ratio for a predetermined block strength is set. Here, as the predetermined block strength, for example, from the viewpoints of the versatility and performance of the block, it is desirable to be 18 N / mm ２ or more. However, the block strength is not limited to this value. The higher the block strength, the more preferable, and there is no particular limitation on its upper limit. For example, it can be 45 N / mm ２ etc. Note that the block strength refers to the mechanical compressive strength (compressive strength) of the block. The compressive strength is calculated in accordance with JIS R 5201 (Physical test methods for cement).

[0045] The key to selecting a low-alkalinity block material is to choose a material that results in a lower pH of the interstitial water than Portland cement, the most widely used block material. As illustrated in Figure 3, based on the above-mentioned α and β, the only material that fits within the selectable range that satisfies the constraints is low-alkalinity cement B, which is selected.

[0046] Typical examples of low-alkali cement additives include calcium aluminate and calcium sulfoaluminate. However, low-alkali cement additives are not limited to these.

[0047] Portland cement is defined in JIS R 5210. An example of the composition of Portland cement, by mass, is 64.8% calcium oxide, 22.0% silicon dioxide, 5.5% aluminum oxide, 3.0% ferric oxide, 1.4% magnesium oxide, and 1.9% sulfur trioxide.

[0048] The pH of the block pore water is measured by measuring a sample obtained using a procedure in accordance with JIS K 0058-1 (Chemical Test Methods for Slags - Part 1: Leaching Test Method (Tank Reaching Test)). The solvent used in this test method is normally pure water, but if the block is used in the sea, artificial seawater may be used.

[0049] The pH of the sample will be measured in accordance with JIS K 0102 (Test Methods for Industrial Wastewater), "12.1 Glass Electrode Method".

[0050] Furthermore, MAP, a typical example of a phosphorus compound, typically experiences decreased solubility above pH 7, and its solubility becomes very low in the pH range of 8.0 to 9.0, which is the pH range used for MAP removal.

[0051] The nutrient-eluting block of this disclosure has a composition that maintains the sustained release of phosphorus compounds such as MAP at a pH that allows the interstitial water pH of the block to be maintained. For this purpose, Portland cement and phosphorus compounds are mixed, and low-alkalinization cement additives such as calcium aluminate and calcium sulfoaluminate are added, so that the pH of the interstitial water of the block is lower than that of the Portland cement.

[0052] The pH of the interstitial water in the nutrient-eluting block of this disclosure is preferably 7 or less. This is to prevent the solubility of MAP from decreasing. Furthermore, the pH of the interstitial water in the block is preferably 6 or less, and preferably 5 or less if it is desirable to increase the supply of phosphorus to seawater, etc.

[0053] Figure 4 is a flow chart showing the details of the phosphorus compound preparation step S300 in Figure 1.

[0054] The phosphorus compound adjustment step S300 involves adjusting the content of the phosphorus compound 5 as a material so that the nutrient elution block 20 shown in Figure 1 meets the appropriate performance requirements. Here, performance refers to the mechanical compressive strength (compressive strength) of the block.

[0055] In Figure 4, the phosphorus compound moisture content confirmation step S310 confirms the moisture content of the phosphorus compound 5 that was delivered in the block material delivery step S220 (Figure 2). The moisture content of the phosphorus compound 5 may be measured on-site at the stock site using a moisture meter, or it may be calculated from the weight before and after drying by sampling a portion. If the moisture content of the phosphorus compound 5 is known at the time of delivery, the phosphorus compound moisture content confirmation step S310 can be omitted.

[0056] In step S320, which involves confirming the upper limit of the phosphorus compound content, the upper limit of the phosphorus compound 5 content that allows the block to meet the required mechanical compressive strength is confirmed. A higher content is desirable for leaching more nutrients and supplying them to the installation area, but this also reduces the mechanical compressive strength. Therefore, in order to satisfy the required mechanical compressive strength, it is essential to determine the upper limit of the content and keep the content below that limit.

[0057] A key feature of setting the upper limit of the phosphorus content in this process is the use of the relationship formula F between the phosphorus compound content P and the concrete block compressive strength S. Here, the phosphorus compound content P is the phosphorus compound content contained in the concrete block.

[0058] The relational equation F is prepared as a functional approximation formula based on test data. Instead of a continuous function, relational equation F may be divided into several numerical ranges for the phosphorus compound content P, and a data table corresponding to the compressive strength S value may be prepared. This relational equation F may be prepared, for example, for each type of cement, which is the main raw material of the block, or for each type of aggregate, such as sand or gravel, which is a secondary material.

[0059] By using this relational equation F, the phosphorus compound content P can be determined for the required concrete block compressive strength S. It is preferable that the content used here be based on dry weight, not wet weight (including moisture). It is important that the required concrete block compressive strength S satisfies a predetermined standard value. Therefore, from the viewpoint of block versatility and performance, the concrete block compressive strength S is set at 18 N / mm². ２ The phosphorus compound content P is calculated within the range that satisfies the above conditions.

[0060] In the phosphorus compound content setting step S330, the staff (workers) of the block manufacturing facility 100 set the content within a range that is less than or equal to the upper limit of the phosphorus compound content P determined in the phosphorus compound content upper limit confirmation step S320, according to the intended use (whether the emphasis is on the amount of nutrients leached out or on mechanical compressive strength).

[0061] The phosphorus compound content P is preferably approximately 5 to 10% by mass. However, the phosphorus compound content P is not limited to this range. The concrete block compressive strength S is 18 N / mm². ２ If the above conditions are met, the phosphorus compound content P may exceed 10% by mass. If the phosphorus compound content P is between 5% and 10% by mass, in most cases the concrete block compressive strength S is 18 N / mm². ２The above is acceptable. The compressive strength S of the concrete block is preferably higher, and there is no particular upper limit, but for example, 45 N / mm². ２ It can be considered to be of a certain degree.

[0062] Figure 5 is a flowchart showing the details of the block manufacturing process S400 in Figure 1.

[0063] In the block manufacturing process S400 shown in Figure 5, the nutrient elution block 20 is manufactured according to the phosphorus compound content set in the phosphorus compound content upper limit confirmation process S320.

[0064] In the first block material mixing step S410, measured cement, aggregate, and phosphorus-recycled phosphorus compounds are placed in a mixer and mixed together with water and, if necessary, pigments.

[0065] Next, in the block molding process S420, the mixed material is supplied from the mixer to the molding machine. The material supplied to the molding machine is placed into a mold in fixed amounts and compacted by vibration and pressure to form the block. At this stage, the block has not yet completely hardened, so in the next block curing process S430, the block is further hardened by heating or other means. In the final block processing process S440, the block is cut into a predetermined shape, and the nutrient salt eluting block 20 is completed.

[0066] By going through these processes, it is possible to manufacture a nutrient-releasing block 20 that effectively utilizes phosphorus compound 5 and supplies phosphate fertilizer components to the target sea area at the required releasing rate. By utilizing this block, it is possible to promote the growth of marine ecosystems such as seaweed beds, increase the amount of carbon dioxide absorbed and stored by blue carbon, and ultimately contribute to decarbonization.

[0067] The effects of this disclosure are summarized below.

[0068] According to this disclosure, the elution rate of MAP and other substances can be increased, thereby increasing the amount of phosphate eluted into seawater that is required.

[0069] Furthermore, it can suppress the formation of calcium hydroxide due to the hydration reaction of Portland cement, etc., mitigate alkalization that inhibits the elution of MAP, and increase the elution rate.

[0070] Furthermore, recycled phosphorus compounds recovered from sewage treatment processes and other sources can be effectively utilized.

[0071] Furthermore, by installing the blocks described in this disclosure in marine ecosystems, it becomes possible to supply the amount of phosphate necessary for blue carbon, thereby promoting the absorption and storage of atmospheric carbon dioxide by marine ecosystems. This can accelerate decarbonization.

[0072] 1: Cement material, 5: Phosphorus compound, 20: Nutrient salt elution block, 100: Block manufacturing facility, S200: Low alkalinity cement material adjustment process, S210: Block material selection process, S220: Block material delivery process, S230: Block material particle size adjustment process, S240: Block material weighing process, S300: Phosphorus compound adjustment process, S310: Phosphorus compound moisture content confirmation process, S320: Phosphorus compound content upper limit confirmation process, S330: Phosphorus compound content setting process, S400: Block manufacturing process, S410: Block material mixing process, S420: Block molding process, S430: Block curing process, S440: Block processing process.

Claims

1. A method for producing a block capable of eluting nutrients by mixing a cement material with a phosphorus compound which is a phosphate capable of eluting phosphated phosphorus, comprising: a step of adjusting the content of a low-alkalization cement additive added to the cement material such that the pH of the immersion liquid of the block is lower than that of Portland cement; and a step of adjusting the content of the phosphorus compound.

2. The method for producing a nutrient-eluting block according to claim 1, wherein the low-alkalization cement additive comprises at least one of calcium aluminate and calcium sulfoaluminate.

3. The method for producing a nutrient-eluting block according to claim 1, wherein the cement material includes Portland cement.

4. The method for producing a nutrient salt elution block according to claim 1, wherein the pH of the immersion liquid of the block is 7 or less.

5. A method for producing a nutrient-eluting block according to claim 1, further comprising the steps of mixing the cement material, the phosphorus compound, and the low-alkalization cement additive, molding the mixture, and producing the block.

6. A nutrient-eluting block comprising: a cement material; a phosphorus compound which is a phosphate capable of eluting phosphated phosphorus; and a low-alkalinity cement additive, wherein the low-alkalinity cement additive is added to the cement material such that the pH of the block's immersion solution is lower than that of Portland cement; and the content of the phosphorus compound is adjusted so that the compressive strength of the block is within a predetermined range.

7. The nutrient elution block according to claim 6, wherein the low-alkalization cement additive comprises at least one of calcium aluminate and calcium sulfoaluminate.

8. The nutrient elution block according to claim 6, wherein the cement material comprises Portland cement.

9. The nutrient elution block according to claim 6, wherein the pH of the immersion liquid of the block is 7 or less.

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