Substrate material for growing seagrass, method for producing substrate for growing seagrass, shallow structure for growing seagrass, and method for constructing shallow structure

Abstract

To provide a substrate material for growing seagrass, a method for producing the substrate for growing seagrass, a shallow structure suitable for seagrass growth, and a method for constructing the shallow structure, which are applicable when nitrogen cannot be supplied from the underlying layer to seagrass such as eelgrass or when the nitrogen supply amount from the underlying layer is insufficient, and which enable suppression of redispersion into mud after immersion in water and resistance to drift caused by waves or tidal currents.SOLUTION: The substrate material for growing seagrass comprises, as a main raw material, granular matter with a particle size of 25 mm or less, which is formed by solidification of a mixed material obtained by mixing dredged soil, steelmaking slag, a strength-increasing agent, and a nitrogen-supplying material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a growth substrate material for seaweeds such as eelgrass, a method for manufacturing a growth substrate for seaweeds, a shallow-bottom structure suitable for seaweed growth, and a method for constructing a shallow-bottom structure.

Background Art

[0002] As a measure against global warming, carbon (blue carbon) taken up by seaweed beds and shallow bottoms has attracted attention. Eelgrass is a seaweed distributed in the sandy mud area of shallow seas, and it has been reported that it grows in places containing gravel even in places with severe wave conditions (Non-Patent Document 5). Since the carbon dioxide absorption coefficient of eelgrass beds where eelgrass grows densely is larger than that of kelp beds and sargassum beds where rocky reefs are formed (Non-Patent Document 1), it is expected to create a shallow bottom suitable for eelgrass growth and create an eelgrass bed. As the establishment conditions of an eelgrass bed, there are water depth (light), bottom sediment, waves, water quality, etc. Nutrients are required for the growth of eelgrass, and nitrogen in the bottom sediment affects the plant height (Non-Patent Document 2).

[0003] Patent Document 1 discloses a modified soil for creating an eelgrass bed in a brackish water area, which is composed of a mixture of dredged sediment and fine-particle-removed steel slag obtained by removing fine particles from steel slag. When there is little nitrogen, phosphorus, etc. in the interstitial water of the dredged sediment, it is described that in addition to the dredged sediment and the fine-particle-removed steel slag, humus soil or the like may be added (paragraph 0031).

[0004] Patent Document 2 discloses a method for constructing a seaweed bed by laying a mixture of blast furnace granulated slag and other bottom sediment materials on the seabed to provide a base for fixing the rhizomes or roots of seaweeds, transplanting seaweeds to the base or sowing seeds of seaweeds to allow the seaweeds to grow and proliferate and form a seaweed bed. It is described that the other bottom sediment materials are one or more selected from natural sand, dredged sediment, bottom sediment soil at the laying site, and slag other than blast furnace granulated slag, and as the slag other than blast furnace granulated slag, there are various slags such as steelmaking slag, municipal waste molten slag, and municipal waste incineration ash molten slag (paragraph 0018).

[0005] Patent Document 3 discloses a method for modifying or constructing a settlement substrate for seagrasses, etc., which supplies silicic acid or / and silicate compounds on or / and in the bottom sediment at the bottom where seagrasses or / and microalgae have settled or are to be settled with seagrasses or / and microalgae. It describes laying slag generated in the steel manufacturing process on the bottom as at least part of the settlement substrate for seagrasses or / and microalgae, and mixing organic matter into the slag generated in the steel manufacturing process laid on the bottom (paragraph 0009).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Non - Patent Documents

[0007]

Non - Patent Document 1

Non - Patent Document 2

Non - Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] In recent years, the creation of shallow fields using calcia-modified soil has been increasing. However, since calcia-modified soil solidifies, it is difficult for the roots of eelgrass to grow. It is necessary to place a material that serves as a growth substrate for eelgrass on the calcia-modified soil to ensure space for the roots and rhizomes of eelgrass to grow. However, as shown in Fig. 10, simply placing a sand covering material consisting only of sand as a growth substrate on calcia-modified soil may result in nitrogen deficiency and suppression of eelgrass growth when nitrogen supply from the underlying calcia-modified soil or the original ground cannot be expected.

[0009] In addition, when there is nitrogen supply from the original seabed, although nitrogen may be supplied from the bottom surface by pouring sand covering material on the original seabed and contribute to the growth of eelgrass, the sand covering material may remudify during underwater pouring or flow out due to waves or tidal currents, and ultimately, it cannot contribute to the growth of eelgrass.

[0010] In addition, there is Hi Beads (registered trademark) made from coal ash as a granular material, which is used for creating eelgrass beds. However, since its wet density (1.0 - 1.4 g / cm 3 ) is relatively small, it may flow out due to waves and currents, and it does not mix a nitrogen supply source.

[0011] In view of the problems of the prior art as described above, the present invention can be applied when nitrogen supply from the lower layer cannot be expected or the nitrogen supply amount from the lower layer is small for seaweeds such as eelgrass, and provides a growth substrate material for seaweeds that is difficult to remudify after underwater pouring and difficult to be washed away by waves and tidal currents, a manufacturing method of the growth substrate material for seaweeds, a shallow field structure suitable for seaweed growth, and a method for creating the shallow field structure.

Means for Solving the Problems

[0012] The growth substrate material for seaweeds for achieving the above object is mainly composed of solidified granular materials with a particle size of 25 mm or less, which are obtained by mixing dredged soil, steelmaking slag, strength enhancer, and nitrogen supply material.

[0013] According to this growth substrate material for seaweeds, even when nitrogen supply from the lower layer cannot be expected or the nitrogen supply amount from the lower layer is small, nitrogen is supplied from the nitrogen supply material to the roots of seaweeds from the growth substrate constructed by underwater pouring of the growth substrate material, so it can contribute to the growth of seaweeds. Since a strength enhancer is mixed, the growth substrate material has a predetermined strength and is difficult to remudify after underwater pouring. Also, because it is a granular material with a particle size of 25 mm or less, it is difficult to be washed away by waves and tidal currents.

[0014] In the above-mentioned seaweed growth substrate material, the strength enhancer is preferably any one of blast furnace slag fine powder, cement, lime, and paper sludge incineration ash, or a combination of any two or more of them.

[0015] It is preferable that the uniaxial compressive strength of the mixed material at 28 days of age is at least 500 kN / m 2 This ensures that the seaweed growth substrate material does not remudify after being put into water.

[0016] The nitrogen supply material is preferably any one of compost, seaweed, sea grass, rice straw, rice husk, wood chip, bamboo chip, and fish meal, or a combination of any two or more of them.

[0017] It is preferable that the nitrogen content of the mixed material is 0.2 kg-N / m 3 or more, or the ammonia nitrogen elution amount (sediment survey method) is 0.3 mg / l or more.

[0018] The method for manufacturing a seaweed growth substrate material for achieving the above object uses a mixed material obtained by mixing dredged soil, steelmaking slag, a strength enhancer, and a nitrogen supply material, cures for a certain period after the mixing, and crushes it to a particle size of 25 mm or less after solidification, or granulates it to a particle size of 25 mm or less during the mixing and then cures and solidifies it for a certain period.

[0019] According to this method for manufacturing a seaweed growth substrate material, a seaweed growth substrate material mainly composed of particulate matter with a particle size of 25 mm or less can be easily manufactured from a mixed material of dredged soil, steelmaking slag, a strength enhancer, and a nitrogen supply material. The growth substrate material put into water can contribute to the growth of seaweed, is difficult to remudify after being put into water, and is difficult to be washed away by waves and tides.

[0020] In the method for manufacturing the seagrass growth substrate material, it is preferable to fix carbon dioxide to the steelmaking slag by supplying carbon dioxide (CO2) to the steelmaking slag before the mixing. Alternatively, during the mixing, carbon dioxide (CO2) may be supplied to the mixed material after crushing or granulation to fix carbon dioxide to the steelmaking slag and the mixed material. By such CO2 fixation, the pH of the mixed material can be suppressed to mitigate the impact on seagrass growth, and furthermore, a carbon storage effect can be expected.

[0021] Also, a carbon-containing material such as biochar may be added to the mixed material, whereby a carbon storage effect can be expected.

[0022] The shallow-bottom structure for achieving the above object is a shallow-bottom structure for seagrass growth, comprising a seagrass growth substrate constructed from the above-mentioned seagrass growth substrate material or a seagrass growth substrate material manufactured by the above-mentioned method for manufacturing the seagrass growth substrate material.

[0023] According to this shallow-bottom structure for seagrass growth, even when nitrogen supply from the lower layer cannot be expected or the nitrogen supply amount from the lower layer is small for the seagrass growth substrate constructed from the seagrass growth substrate material, nitrogen is supplied from the nitrogen supply material to the roots of the seagrass by the growth substrate, so it can contribute to the growth of the seagrass. Since a strength enhancer is mixed, the growth substrate material has a predetermined strength and is difficult to remud after being put into water. Also, being granular with a particle size of 25 mm or less makes it difficult to be washed away by waves and tidal currents. Such a shallow-bottom structure can efficiently create a eelgrass bed.

[0024] It is preferable that the above shallow-bottom structure further includes a lower layer constructed on the original ground, and the growth substrate is constructed as an upper layer on the lower layer. In this case, the lower layer preferably consists of a modified soil obtained by mixing dredged soil and steelmaking slag.

[0025] Further, the growth substrate may be constructed on the original ground or on an artificial bio-reef. This is preferably applied when nitrogen supply from the original ground cannot be expected or when the nitrogen supply amount from the original ground is small. Seagrass can grow on the growth substrate constructed on the original ground. Also, seagrass can grow on the growth substrate of seagrass in the artificial bio-reef.

[0026] In addition, in the shallow structure for seagrass growth, it is preferable that the thickness of the growth substrate is 5 to 50 cm.

[0027] A method for constructing a shallow structure for achieving the above object is a method for constructing a shallow structure for seagrass growth, which involves throwing the above-mentioned seagrass growth substrate material or the seagrass growth substrate material manufactured by the above-mentioned method for manufacturing the seagrass growth substrate material into water to construct a seagrass growth substrate.

[0028] According to this method for constructing a shallow structure for seagrass growth, a seagrass growth substrate can be constructed from the seagrass growth substrate material. Even when nitrogen supply from the lower layer cannot be expected or when the nitrogen supply amount from the lower layer is small, nitrogen is supplied to the roots of seagrass by the nitrogen supply material from the growth substrate, so it can contribute to the growth of seagrass. Since a strength enhancing material is mixed, the growth substrate material has a predetermined strength and is difficult to remud after being thrown into water. Also, because it is granular with a particle size of 25 mm or less, it is difficult to be washed away by waves and tidal currents. Such a shallow structure can efficiently create a seagrass bed.

[0029] In the above method for constructing a shallow structure, it is preferable to throw a modified soil mixed with dredged soil and steelmaking slag into water to construct a lower layer on the original ground, and then construct the seagrass growth substrate as an upper layer on the lower layer.

[0030] Further, the growth substrate may be constructed on the original ground or on an artificial bio-reef.

Advantages of the Invention

[0031] According to the present invention, it can be applied when the supply of nitrogen from the lower layer cannot be expected for seagrasses such as eelgrass or when the supply amount of nitrogen from the lower layer is small, and it is difficult to re-mud after being put into water and is difficult to be washed away by waves or tidal currents. A growth substrate for seagrasses, a method for manufacturing a growth substrate for seagrasses, a shallow-bottom structure suitable for seagrass growth, and a method for constructing a shallow-bottom structure can be provided.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying out the Invention

[0033] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a shallow field structure for eelgrass growth according to this embodiment.

[0034] As shown in FIG. 1, a shallow field structure 10 for eelgrass growth, such as eelgrass, includes a lower layer 11 constructed on the original ground G using a modified soil that is a mixture of dredged soil and steelmaking slag, a growth base 12 of eelgrass and the like constructed as an upper layer on the lower layer 11 using a growth base material for eelgrass and the like, and a submerged breakwater 13 constructed on the original ground G on the offshore side. The lower layer 11 and the growth base (upper layer) 12 of eelgrass are laminated and installed on the seabed with a shallow water depth between the quay wall Q and the submerged breakwater 13.

[0035] The growth base material for eelgrass that constitutes the upper layer 12 in FIG. 1 is mainly made of granular materials with a particle size of 25 mm or less, which are manufactured by solidifying a mixed material obtained by mixing dredged soil, steelmaking slag, a strength enhancer, and a nitrogen supply material.

[0036] The shallow field structure 10 in FIG. 1 can be constructed by building a submerged breakwater 13 on the original ground G away from the quay wall Q towards the offshore side so as to extend substantially parallel to the quay wall Q. Next, a modified soil obtained by mixing dredged soil and steelmaking slag is poured into the water to construct the lower layer 11 on the original ground G. Then, a growth base material for eelgrass mainly made of granular materials with a particle size of 25 mm or less composed of a mixed material is poured into the water, and an upper layer (growth base of eelgrass) 12 is constructed on the lower layer 11.

[0037] The thickness of the upper layer (growth base of eelgrass) 12 in FIG. 1 is preferably 5 - 50 cm, more preferably 10 - 30 cm.

[0038] It is preferable to use any one of blast furnace slag fine powder, cement, lime, and paper sludge incineration ash (PS ash), or to use a combination of at least any two of them. By mixing such a strength enhancer, the growth substrate material for seagrass has a predetermined strength and is difficult to remudify after being put into water. None of Patent Documents 1 to 3 disclose the strength of the growth substrate material for preventing remudification during water input.

[0039] If it is a low-strength mixed material, the strength may gradually decrease and remudify after being put into water. However, when the uniaxial compressive strength of the mixed material at 28 days (after 28 days of mixing) is at least 500 kN / m 2 it will not remudify after being put into water. The mixing amount of the strength enhancer in the mixed material is determined by a preliminary mixing test so that the uniaxial compressive strength of the mixed material at 28 days is at least 500 kN / m 2 is achieved.

[0040] As the nitrogen supply material, it is preferable to use any one of compost, seaweed, seagrass, rice straw, rice husk, wood chip, bamboo chip, and fish meal, or a combination of at least any two of them. Also, it is desirable that the nitrogen content of the mixed material is 0.2 kg-N / m 3 or more, or the ammonia nitrogen elution amount (substrate survey method) is 0.3 mg / l or more.

[0041] As a method for growing eelgrass on the growth substrate 12 of the shallow field structure 10 in FIG. 1, general eelgrass bed construction methods such as sowing eelgrass seeds on the growth substrate 12 or transplanting eelgrass seedlings or stocks can be applied ( "Eelgrass Bed Restoration Handbook", Mie Prefectural Fisheries Research Institute, etc., https: / / www.pref.mie.lg.jp / common / content / 000661738.pdf)

[0042] FIG. 2 is a cross-sectional view schematically showing the nitrogen supply state in the shallow-bottom structure 10 of FIG. 1 and the growth state of seaweeds such as eelgrass. Even when there is no nitrogen supply from the lower layer 11 and the original ground G in FIG. 2 or when the nitrogen supply amount is small, in the growth base (upper layer) 12 composed of the growth base material for seaweeds, nitrogen is supplied from the nitrogen supply material mixed in the growth base material to the whisker-like roots 16 extending from the rhizome 15 of the eelgrass ZM in the direction of arrow a in the figure, so that it can contribute to the growth of the eelgrass ZM. That is, the growth base material for seaweeds mainly composed of particulate matter with a particle size of 25 mm or less of the mixed material according to the present embodiment is preferably applied when nitrogen supply from the lower layer where the growth base material for seaweeds is laid cannot be expected for seaweeds such as eelgrass or when the nitrogen supply amount from the lower layer is small. The shallow-bottom structure 10 can efficiently create an eelgrass bed.

[0043] FIG. 3 shows another shallow-bottom structure 20 according to the present embodiment. The shallow-bottom structure 20 in FIG. 3 is constructed by directly introducing the growth base material for seaweeds according to the present embodiment onto the original ground G to form a seaweed growth base 14 similar to the growth base 12 in FIG. 1. In the seaweed growth base 14, nitrogen is supplied from the nitrogen supply material mixed in the growth base material to the whisker-like roots 16 extending from the rhizome 15 of the eelgrass ZM, so that it can contribute to the growth of the eelgrass ZM. Therefore, the shallow-bottom structure 20 is preferably applied when there is no nitrogen supply from the original ground G or when the nitrogen supply amount is small. Note that the shallow-bottom structure 20 may be constructed by directly introducing the growth base material for seaweeds onto the constructed biological symbiotic revetment instead of the original ground to form the seaweed growth base 14. The shallow-bottom structure 20 can efficiently create an eelgrass bed.

[0044] The growth base material for seaweeds according to the present embodiment uses particulate matter with a particle size of 25 mm or less of the mixed material as the main raw material, so it is difficult to be washed away by waves and tidal currents. Also, although it is initially alkaline, due to its coarse granular shape and the pH buffering effect in seawater, the increase in pH is suppressed. Such particulate matter with a particle size of 25 mm or less contains fine particles generated in the manufacturing process of crushing and granulation. However, since seaweeds such as eelgrass grow in the sandy mud area and the bottom sediment also contains those with a particle size of 0.45 μm or less, there is no problem even if it contains fine particles.

[0045] By using a growth substrate material with a relatively large particle size, it is possible to suppress the outflow of the growth substrate material due to waves and currents during high-wave periods. The conditions for suppressing such outflow of the growth substrate material will be examined. There is a Shields number Ψ as an index representing the suitable growth area for eelgrass (see Non-Patent Document 3). Ψ < 0.1: Does not move 0.1 < Ψ < 0.2: Sweep flow state (sand particles roll on the seabed) 0.2 < Ψ < 0.5: Suspended movement (sand particles are suspended and sand reefs are formed) 0.5 < Ψ: Sheet flow (sand moves in layers) The Shields number Ψ is a dimensionless quantity indicating the ease of movement of the seabed sediment due to waves, and is the ratio of the external force (bottom shear stress) due to waves or tidal currents attempting to move the seabed sediment to the resistance force due to the self-weight of the seabed sediment, and is expressed as the following formula (1). Ψ = (1 / 2)×ρf cw u 2 / ((ρ s - ρ)gD) (1) However, Ψ: Shields number, ρ: Density of seawater, ρ s : Density of bottom sediment soil particles, g: Acceleration due to gravity (m / s 2 ), D: Median grain size of the bottom sediment (mm), u: Bottom wave flow velocity (m / s), f cw u: Friction coefficient, is.

[0046] The roots and rhizomes of eelgrass extend into the sandy mud. However, when the Shields number becomes large, exceeds 0.5, and enters the sheet flow state, the sandy mud where the roots and rhizomes are distributed is lost, and the eelgrass will flow out. As a condition for suppressing the outflow of eelgrass, the Shields number of 0.2 is often used as an index (see Non-Patent Document 4). Therefore, it is desirable to produce a growth substrate material with a Shields number of 0.2 or less. For example, for the conditions of the sea area with a water depth of 3.0 m, a wave height of 2 m, a period of 6 seconds, and the density of the growth substrate material of 2.0 g / cm 3As a result, when the condition for the number of shields to be 0.2 or less is obtained from the above formula (1), the median particle size becomes 2 mm or more. Under the conditions of such a sea area, it can be seen that the seagrass growth base material using, as the main raw material, particulate matter with a particle size of 25 mm or less and a median particle size of, for example, 5 mm according to the present embodiment can achieve suppression of the outflow of eelgrass.

[0047] Next, a method for manufacturing the seagrass growth base material according to the present embodiment will be described with reference to FIGS. 4 and 5. The method for manufacturing the seagrass growth base material in FIG. 4 includes a step (S01) of mixing each material of dredged soil, steelmaking slag, strength enhancer, and nitrogen supply material, a step (S02, S03) of curing the mixed material for a certain period after mixing to solidify the mixed material, a step (S04) of crushing the solidified mixed material to a particle size of 25 mm or less, and a step (S05) of obtaining a large number of particulate matters with a particle size of 25 mm or less.

[0048] Another method for manufacturing the seagrass growth base material in FIG. 5 includes a step (S11) of mixing each material with a mixer, a step (S12) of granulating the mixed material to a particle size of 25 mm or less using the mixed material during this mixing, a step (S13, S14) of curing the granulated mixed material for a certain period to solidify it, and a step (S15) of obtaining a large number of particulate matters with a particle size of 25 mm or less.

[0049] Note that a carbon-containing material such as biochar may be added during the mixing of each material in FIGS. 4 and 5, and thereby, a carbon storage effect can be expected. The carbon-containing material preferably has a carbon content of at least 10% by mass.

[0050] Also, in FIGS. 4 and 5, steelmaking slag that has fixed CO2 in advance (before mixing) may be used. Also, CO2 may be fixed during the mixing, after crushing, and after granulation of the mixed material. Such CO2 fixation will be described with reference to FIGS. 6 to 8.

[0051] Figure 6 is a schematic diagram (a) showing an example of using the exhaust gas of a plant for CO2 fixation before mixing with steelmaking slag and for CO2 fixation with particulate matter in FIGS. 4 and 5, and a schematic diagram (b) similarly showing an example of using the exhaust gas of an excavator or a generator. As shown in FIG. 6(a), for the steelmaking slag SS stored in the steelmaking slag CO2 fixation yard 30, the exhaust gas, which is a CO2-containing gas discharged from the plant PL, is supplied through the CO2 supply pipe 32 by the CO2 supply device 31. Also, as shown in FIG. 6(b), for the steelmaking slag SS stored in the steelmaking slag CO2 fixation yard 30, the exhaust gas, which is a CO2-containing gas discharged from the excavator BH or the generator GP, is supplied through the CO2 supply pipe 32 by the CO2 supply device 31. The CO2 supply pipe 32 is preferably composed of a plurality of pipes having a large number of holes, and is installed in advance at the bottom of the steelmaking slag CO2 fixation yard 30, and the steelmaking slag SS is stacked and stored thereon.

[0052] As shown in FIGS. 6(a) and (b), the calcium (Ca) contained in the steelmaking slag SS reacts with the CO2 in the supplied exhaust gas and is chemically fixed as calcium carbonate (CaCO3) or the like. Then, the steelmaking slag SS is mixed with other materials in step S01 of FIG. 4 and step S11 of FIG. 5, and thereafter, the CO2 is physically and stably retained in the solidified mixed material.

[0053] Note that examples of the plant PL in FIG. 6(a) include blast furnaces, converters, thermal power plants, petroleum refineries, cement plants, asphalt plants, incineration facilities, compost manufacturing plants, etc. The excavator BH in FIG. 6(b) may be other construction machines or mixer trucks, etc. Also, instead of the steelmaking slag SS in FIGS. 6(a) and (b), the exhaust gas may be supplied to the particulate matter in FIG. 4 or the particulate matter in FIG. 5, and the CO2 may be reacted and fixed with the calcium (Ca) eluted from the steelmaking slag and contained in the particulate matter.

[0054] FIG. 7 is a schematic diagram showing an example of using the exhaust gas of a mixer truck or a generator for CO2 fixation during mixer mixing in FIG. 5 or for CO2 fixation on the granular materials in FIGS. 4 and 5. Each material is supplied to the rotating drum 40 of the mixer truck MD in FIG. 7 and mixed, and after passing through the granulation process, it becomes granular. However, the exhaust gas, which is a CO2-containing gas discharged from the mixer truck MD or the generator, is supplied from the CO2 supply device 31 through the CO2 supply pipe 41 to the mixed material MM in the rotating drum 40. Calcium (Ca) contained in the steelmaking slag reacts with CO2 contained in the exhaust gas and is chemically fixed as calcium carbonate (CaCO3), etc., and CO2 is physically and stably retained in the solidified granular mixed material. Note that dry ice may be introduced instead of the exhaust gas during mixing. Further, FIG. 7 shows a configuration in which the exhaust gas is supplied during material mixing in the rotating drum 40 of the stopped mixer truck MD. However, the CO2 supply device 31 may be mounted on the mixer truck MD, and the exhaust gas may be supplied inside the moving mixer truck MD, or dry ice may be introduced. Further, the exhaust gas may be supplied to the granular material in FIG. 4 or the granular material in FIG. 5 instead of the mixed material MM, and CO2 may be reacted with calcium (Ca) eluted from the steelmaking slag and contained in the granular material to be fixed.

[0055] FIG. 8 is schematic diagrams (a) and (b) showing an example of performing CO2 fixation on steelmaking slag and the granular materials in FIGS. 4 and 5 using dry ice, and a schematic diagram (c) showing an example of performing the same on a gut boat. As shown in FIG. 8(a), dry ice 51 is laid on the CO2 fixation yard 50. Next, as shown in FIG. 8(b), the steelmaking slag SS is laid on the dry ice 51 of the CO2 fixation yard 50, and CO2 generated by the vaporization of the dry ice 51 is supplied to the steelmaking slag SS, and CO2 is fixed to the steelmaking slag SS. Further, as shown in FIG. 8(c), a CO2 fixation yard 50 similar to that in FIG. 8(a) may be provided on the gut boat GT, the steelmaking slag SS may be laid on the dry ice 51, and CO2 may be fixed to the steelmaking slag SS in the same manner as in FIG. 8(b). Note that the dry ice and the steelmaking slag may be laid in multiple layers.

[0056] According to the examples of FIGS. 8(a) to 8(c), by appropriately setting the laying amounts (laying thicknesses) of the dry ice 51 and the steelmaking slag SS, the CO2 emission amount from the dry ice 51 and the CO2 fixation amount in the steelmaking slag SS can be controlled, and it is possible to avoid wastefully releasing CO2 into the atmosphere.

[0057] Further, in FIGS. 8(a) to 8(c), instead of the steelmaking slag SS, the granular material of FIG. 4 or the granular material of FIG. 5 may be laid on the dry ice 51, and CO2 may be reacted with calcium (Ca) eluted from the steelmaking slag and contained in the granular material for fixation.

[0058] By fixing CO2 in FIGS. 6 to 8, the pH of the mixed material can be suppressed to mitigate the influence on the growth of seagrass, and further, a carbon storage effect can be expected. Also, a carbon storage effect can be expected by adding a carbon-containing material when mixing the materials of FIGS. 4 and 5. Furthermore, since the organic matter contained in the nitrogen supply material is solidified in the mixed material and microbial decomposition is suppressed under high-alkali conditions, a carbon storage effect can be expected.

[0059] As described above, the seagrass growth substrate according to the present embodiment can be made into a carbon-negative material by CO2 fixation, addition of a carbon-containing material, etc., and it is possible to promptly exhibit a carbon storage effect as blue carbon by the growth of seagrass.

[0060] (Experimental Example) Next, the present invention will be specifically described with reference to experimental examples, but the present invention is not limited to these experimental examples.

[0061] Experimental Example 1 Using dredged soil (water content ratio 163%, liquid limit 65.3%), with a dredged soil volume mixing ratio of 50% and 1066 kg / m of steelmaking slag with a particle size of 9.5 mm 3 , 421 kg / m of blast furnace slag fine powder as a strength enhancer 3 was mixed (wet density 2.0 g / cm 3 ), and compost was used as a nitrogen supply material at 50, 100, and 150 kg / m on an external basis3 When added, and compost is 90 kg / m by external division 3 · 10 kg / m of fish meal 3 For each mixed material when added, a nitrogen content measurement test and a uniaxial compression test (JIS A1216:2020) were carried out 28 days after mixing. The measurement results of the 28-day uniaxial compression strength and nitrogen content are shown in Fig. 9.

[0062] Experimental Example 2 Using dredged soil (water content ratio 131%, liquid limit 65.3%), with a dredged soil volume mixing ratio of 50%, 827 kg / m of steelmaking slag with a particle size of 9.5 mm 3 , 612 kg / m of blast furnace slag fine powder as a strength enhancer 3 were mixed (wet density 2.0 g / cm 3 ). For the mixed material with rice husks added as a nitrogen supply material at 50 kg / m by external division 3 , a nitrogen content measurement test and a uniaxial compression test (JIS A1216:2020) were carried out 28 days after mixing. The measurement results of the 28-day uniaxial compression strength and nitrogen content are shown together in Fig. 9.

[0063] The 28-day uniaxial compression strength of the material without the nitrogen supply material in Experimental Example 1 is 7210 kN / m 2 , and the strength decreases with the addition of compost and fish meal. It can be seen from Fig. 9 that at least 500 kN / m 2 of the 28-day uniaxial compression strength was obtained, including the case of rice husks in Experimental Example 2. Also, since the nitrogen content of the nitrogen supply material is compost 1.5% > rice husks 0.4%, there is a difference in the nitrogen content of the seaweed growth base material. However, it can be seen from Fig. 9 that the nitrogen content is 0.2 kg-N / m in both Experimental Examples 1 and 2 3 or more of the mixed material.

[0064] Experimental Example 3 For each of the mixed materials when using dredged soil (water content ratio 131%, liquid limit 65.3%), steelmaking slag, and CO₂-fixed steelmaking slag, the mixing conditions, pH (JGS 0211), CO₂ emissions of the materials, uniaxial compressive strength at 28 days of age (JIS A1216:2020), and for the granular material after crushing, seaweed (Corethron spp. 5 plants per case, average leaf area 17.6 cm 2 ) was planted in seawater, and the leaf area measured one month later is shown in Table 1 below. Also, for the case of adding compost in Table 1, the growth status of the seaweed planted in a container with a diameter of 7.5 cm one month later is shown in the photograph in Figure 11.

[0065]

Table 1

[0066] As can be seen from Table 1 and Figure 11, by adding compost, the leaf area of Corethron spp. increased compared to the case of only dredged soil or without adding compost, and it grew well. Also, by using CO₂-fixed steelmaking slag, the pH decreased and the CO₂ emissions of the materials became smaller. Note that the following values were used for the calculation of CO₂ emissions. Steelmaking slag: 2.6 kg-CO₂ / t Fine powder of blast furnace slag: 39.6 kg-CO₂ / t Compost: 147 kg-CO₂ / t

[0067] Experimental Example 4 Dredged soil (water content ratio 131%, liquid limit 65.3%), steelmaking slag, and CO₂-fixed steelmaking slag were used, and commercially available compost and seaweed (fresh Undaria pinnatifida) were added externally as nitrogen supply materials. The mixing conditions of the mixed materials, uniaxial compressive strength (JIS A1216:2020), and measurement results of ammonia nitrogen elution amount (sediment survey method) are shown in Table 2 below. Note that for fresh Undaria pinnatifida, the amount of water contained was calculated, and the water content was taken into account and adjusted to a predetermined dredged soil water content ratio.

[0068]

Table 2

[0069] As a result of the test, it can be seen from Table 2 that the uniaxial compressive strength at 28 days of the material age is 500 kN / m 2 or more, and the elution amount of ammonia nitrogen is 0.3 mg / l or more.

[0070] Although the embodiments and experimental examples for carrying out the present invention have been described as above, the present invention is not limited thereto, and various modifications are possible within the scope of the technical idea of the present invention. For example, in the present embodiment, eelgrass has been described as an example of seagrass, but the present invention is not limited to eelgrass and can also be applied to other seagrasses (such as core eelgrass, ribbon eelgrass, etc.).

[0071] The seagrass growth base material according to the present embodiment is mainly composed of granular materials with a particle size of 25 mm or less obtained by solidifying a mixed material obtained by mixing dredged soil, steelmaking slag, strength enhancer, and nitrogen supply material, and a small amount of other materials may be added to such granular materials, but there may also be cases where no other materials are added.

Industrial Applicability

[0072] According to the present invention, it is possible to promote the growth of seagrass such as eelgrass, efficiently create an eelgrass bed, and expect the carbon storage effect as blue carbon due to the growth of seagrass such as eelgrass.

Explanation of Signs

[0073] 10, 20 shallow field structure 11 lower layer 12 seagrass growth base, upper layer 13 submerged breakwater 14 seagrass growth base 15 eelgrass rhizome 16 eelgrass root G original ground Q quay wall SS steelmaking slag ZM eelgrass

Claims

1. A growth substrate for seagrasses, comprising as the main raw material granular materials with a particle size of 25 mm or less obtained by solidifying a mixed material containing dredged soil, steelmaking slag, strength enhancer, and nitrogen supply material.

2. The growth substrate for seagrasses according to claim 1, wherein the strength enhancer is any one of blast furnace slag fine powder, cement, lime, and paper sludge incineration ash, or a combination of any two or more thereof.

3. The uniaxial compressive strength of the above-mentioned admixture at 28 days of age is at least 500 kN / m ２ The seaweed growth substrate according to claim 1, which is such.

4. The growth substrate for seagrasses according to claim 1, wherein the nitrogen supply material is any one of compost, seaweed, seagrass, rice straw, rice husk, wood chip, bamboo chip, and fish meal, or a combination of any two or more thereof.

5. The nitrogen content of the above-described mixed material is 0.2 kg-N / m ３ or more, or the elution amount of ammonia nitrogen (sediment survey method) is 0.3 mg / l or more, and the seagrass growth substrate according to claim 1.

6. A method for manufacturing a growth substrate for seagrasses, using a mixed material containing dredged soil, steelmaking slag, strength enhancer, and nitrogen supply material, curing the mixture for a certain period after mixing, crushing it to a particle size of 25 mm or less after solidification, or granulating it to a particle size of 25 mm or less during mixing and then curing and solidifying it for a certain period.

7. The method for manufacturing a growth substrate for seagrasses according to claim 6, wherein carbon dioxide is supplied to the steelmaking slag before mixing to fix carbon dioxide in the steelmaking slag.

8. The method for manufacturing a growth substrate for seagrasses according to claim 6, wherein carbon dioxide is supplied to the mixed material during mixing, after crushing, or after granulating to fix carbon dioxide in the steelmaking slag and the mixed material.

9. The method for manufacturing a growth substrate for seagrasses according to claim 6, wherein a carbon-containing material is added.

10. A shallow field structure for seagrass growth, comprising: a growth substrate for seagrasses according to any one of claims 1 to 5, or a growth substrate for seagrasses manufactured by the method for manufacturing a growth substrate for seagrasses according to any one of claims 6 to 9.

11. further comprising a lower layer constructed on the original ground, wherein the growth substrate is constructed as an upper layer on the lower layer, as described in claim 10.

12. The shallow field structure according to claim 11, wherein the lower layer is made of modified soil obtained by mixing dredged soil and steelmaking slag.

13. The shallow field structure according to claim 10, wherein the growth substrate is constructed on the original ground or on an artificial reef for symbiotic organisms.

14. The shallow field structure according to claim 10, wherein the thickness of the growth substrate is 5 to 50 cm.

15. A method for constructing a shallow field structure for seagrass growth, comprising: A method for constructing a shallow field structure for constructing a seagrass growth substrate by throwing into water a seagrass growth substrate according to any one of claims 1 to 5, or a seagrass growth substrate produced by the method for producing a seagrass growth substrate according to any one of claims 6 to 9.

16. Throwing into water a modified soil obtained by mixing dredged soil and steelmaking slag to construct a lower layer on the original ground, Next, the method for constructing a shallow field structure according to claim 15, wherein the seagrass growth substrate is constructed as an upper layer on the lower layer.

17. The method for constructing a shallow field structure according to claim 15, wherein the growth substrate is constructed on the original ground or on a constructed biological symbiotic revetment.

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