Floating artificial wetland

Abstract

To provide a floating constructed wetland that can be easily installed and can exhibit an enhanced action of water purification.SOLUTION: A floating constructed wetland 1 is installed in a water area 2 in a floating manner. The floating constructed wetland 1 has a plurality of granular substrates 10, a housing 20 for accommodating the plurality of substrates 10, and plants 30 to be planted in the plurality of substrates 10. The plants 30 have their roots to settle in the gaps among the plurality of substrates 10.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a floating artificial wetland.

Background Art

[0002] As a method for purifying water quality in waters such as lakes and rivers, artificial floating islands in which a base planted with plants is floated in the water area to be purified are known (see, for example, Patent Document 1 and Patent Document 2). Further, as another method, an artificial wetland system having a plurality of subsurface-flow artificial wetlands arranged so that the water to be purified sequentially flows through is known (see, for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the artificial floating islands described in Patent Documents 1 and 2, plants root in the water through the base, thereby exhibiting a water purification effect by absorbing nutrients such as nitrogen and phosphorus in the water or decomposing organic substances. However, depending on the water area to which the artificial floating island is applied, a higher water purification effect may be required. In addition, the installation of the artificial wetland described in Patent Document 3 requires securing a large installation site and involves a large number of man-hours associated with large-scale construction. Therefore, it is desired to facilitate installation and improve the water purification effect.

[0005] An object of the present disclosure is to provide a floating artificial wetland that facilitates installation and can exhibit a higher water purification effect.

Means for Solving the Problem

[0006] A floating artificial wetland according to one aspect of the present disclosure is a floating artificial wetland installed by floating in a water area, and includes a plurality of granular base materials, a housing portion that houses the plurality of base materials, and a plant body planted on the plurality of base materials, and the roots of the plant body take root in the gaps between the plurality of base materials.

[0007] The roots of the plant body in this floating artificial wetland take root in the gaps defined by the plurality of base materials. As a result, due to the rhizosphere effect, many microorganisms accumulate not only around the roots of the plant body but also in the gaps between the plurality of base materials and the plurality of base materials. Since the microorganisms accumulated by the rhizosphere effect have a water purification effect, the floating artificial wetland can exhibit a higher water purification effect due to the accumulation of many microorganisms. In addition, the floating artificial wetland is installed by floating in the water area. Therefore, it is not necessary to prepare a separately large installation location outside the water area like an artificial wetland provided on land, and large-scale construction is not required. Therefore, the floating artificial wetland can be easily installed compared to an artificial wetland installed on land. As described above, this floating artificial wetland facilitates installation and can exhibit a higher water purification effect.

[0008] In one embodiment, each of the plurality of base materials may be porous. In this case, the microorganisms accumulated by the rhizosphere effect can enter each of the porous plurality of base materials. Therefore, more microorganisms can be retained in the floating artificial wetland, so that the floating artificial wetland can exhibit an even higher water purification effect.

[0009] In another embodiment, the housing portion may be provided with an opening through which the water in the water area can enter the housing space defined by the housing portion. In this case, when the water in the water area enters the housing portion through the opening provided in the housing portion, the plurality of base materials in the housing space are flooded. Therefore, water can be supplied into the housing portion only by floating the floating artificial wetland in the water area.

[0010] In yet another embodiment, the floating artificial wetland may further include a floating body portion that floats the housing portion in the water area. For example, with only a plurality of base materials, the housing portion, and the plant body, it may not be possible to float the floating artificial wetland in the water area due to their weight. Since the floating artificial wetland is provided with the floating body portion, even if the plurality of base materials, the housing portion, and the plant body are heavy, the floating artificial wetland can be floated in the water area. Therefore, the degree of freedom in the configuration of the plurality of base materials, the housing portion, and the plant body can be increased.

[0011] In yet another embodiment, the floating body portion may be detachably provided to the housing portion. For example, as the plant body grows, the weight of the floating artificial wetland may change. In such a case, it may be necessary to adjust the floating position of the floating artificial wetland. According to the above configuration, since the floating body portion can be attached to and detached from the housing portion, it can be replaced with an appropriate floating body portion according to the weight of the floating artificial wetland. Therefore, it is possible to flexibly respond to changes in the weight of the floating artificial wetland.

[0012] In yet another embodiment, a part of the plant body may be exposed above the water. In this case, the part of the plant body exposed above the water can exhibit the transpiration effect. Therefore, the amount of water in the water area can be reduced by the transpiration effect of the plant body.

[0013] In yet another embodiment, the plant body may be an aquatic plant having resistance to sewage. In this case, since the plant body has resistance to sewage, the floating artificial wetland can be installed in the sewage area and the sewage area can be purified.

Advantages of the Invention

[0014] According to one aspect and embodiment of the present disclosure, installation can be facilitated and a higher water purification effect can be exhibited.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0016] Hereinafter, embodiments will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted. The dimensional ratios in the drawings do not necessarily match the dimensional ratios of the configurations shown in the following description. "Upper", "lower", "left", and "right" indicate directions based on the illustrated state and are used for convenience. The X direction and the Y direction in each figure are horizontal directions, and the Z direction is a vertical direction. The X direction, the Y direction, and the Z direction are axial directions orthogonal to each other in a three-dimensional orthogonal coordinate system. Hereinafter, the Z direction is also referred to as the vertical direction.

[0017] [Configuration of Floating Artificial Wetland] Referring to FIGS. 1 and 2, the configuration of a floating artificial wetland according to an embodiment will be described. FIG. 1 is a cross-sectional view showing an example of a floating artificial wetland according to an embodiment. FIG. 2 is a bottom view of the floating artificial wetland shown in FIG. 1. The floating artificial wetland 1 shown in FIGS. 1 and 2 is installed by floating in the water area 2. Floating means the state in which the floating artificial wetland 1 is floating. In other words, it refers to the state in which the floating artificial wetland 1 is not in contact with the bottom of the water area 2. When the floating artificial wetland 1 is installed in the water area 2, for example, a part of the member (part) constituting the floating artificial wetland 1 is located above the water surface of the water area 2. The floating artificial wetland 1 has a water purification function, and for example, purifies the water quality of the water area 2 by reducing nutrients such as nitrogen and phosphorus, reducing organic substances, and reducing hardly decomposable organic substances. Examples of hardly decomposable organic substances include humic substances such as humic acid, polycyclic aromatic hydrocarbons, and POPs (persistent organic pollutants).

[0018] The water area 2 is a water area to be purified, and refers to an area where water is stored or an area where water is flowing. The water area 2 may be a naturally formed area such as a lake, a pond, a river, and the sea, or may be an artificially formed area such as a water tank, a reservoir, and a dam lake. The concentrations of nutrients such as nitrogen and phosphorus, and the concentration of organic substances are measured, and a water area where each measured concentration is equal to or higher than a predetermined standard may be selected as the water area 2. The concentration of hardly decomposable organic substances is measured, and a water area where the measured concentration is equal to or higher than a predetermined standard may be selected as the water area 2. Hereinafter, when referring to "the water of the water area 2", it may refer to the liquid in the water area 2 containing nutrients, organic substances, and hardly decomposable organic substances. The above-mentioned predetermined standard is a value appropriately determined by, for example, an organization that manages the water area.

[0019] The floating artificial wetland 1 includes a plurality of base materials 10, a housing part 20, a plant body 30, and a floating part 40.

[0020] Each of the plurality of base materials 10 has a granular shape. In the present embodiment, the granular shape is such that when the plurality of base materials 10 are stacked, gaps can occur between the plurality of base materials 10. Examples of such shapes include polyhedral shapes and spherical shapes. The shapes of the plurality of base materials 10 may be different from each other or the same as each other. Some of the plurality of base materials 10 may have the same shape, and the other base materials 10 may have different shapes. Each base material 10 has a size of, for example, about several millimeters to a dozen or so centimeters.

[0021] Each of the plurality of base materials 10 is porous. That is, each of the plurality of base materials 10 is provided with depressions or pores into which microorganisms contained in the water in the water area 2 can enter and accumulate. Each of the plurality of base materials 10 is formed of, for example, a material with a low specific gravity. Each of the plurality of base materials 10 has a specific gravity smaller than that of the water in the water area 2, for example. Examples of the constituent material of the base material 10 include foamed glass, activated carbon, and biochar. Each of the plurality of base materials 10 can hold (carry) microorganisms.

[0022] The housing portion 20 is a member for housing the plurality of base materials 10. The housing portion 20 defines a housing space 20a and houses the plurality of base materials 10 in the housing space 20a. The housing portion 20 has, for example, a box shape that opens upward. The housing portion 20 has, for example, four side walls 21 extending in the Z direction and a bottom wall 22 connected to the lower ends of the four side walls 21, respectively. Each of the side walls 21 and the bottom wall 22 has, for example, a rectangular plate shape. Each side wall 21 is provided along the periphery of the bottom wall 22 and is connected to two adjacent side walls 21. The housing space 20a is a space surrounded by the four side walls 21 and the bottom wall 22.

[0023] The floating artificial wetland 1 further includes a net-like member 23 that covers the inner surfaces of each side wall 21 and the bottom wall 22. The net-like member 23 is provided, for example, along the four side walls 21 and the bottom wall 22 facing the accommodation space 20a. The net-like member 23 is provided, for example, within the accommodation space 20a. The net-like member 23 is fixed to the four side walls 21 and the bottom wall 22, for example. The net-like member 23 is, for example, a net provided with a plurality of openings. The size of the openings is smaller than the size of the base material 10. The plurality of base materials 10 are loaded on the upper surface of the bottom wall 22 within the accommodation space 20a via the net-like member 23 and are accommodated within the accommodation space 20a of the accommodating portion 20. For example, when the specific gravity of the base material 10 is smaller than the specific gravity of the water in the water area 2, the opening above the accommodating portion 20 may be further covered with the net-like member 23 so that the base material 10 does not move out of the accommodation space 20a from the opening above the accommodating portion 20.

[0024] The accommodating portion 20 is, for example, a net cage. The accommodating portion 20 is provided with openings 21a and 22a. Specifically, a plurality of openings 21a are provided in each side wall 21, and a plurality of openings 22a are provided in the bottom wall 22. The opening 21a penetrates the side wall 21 so that the external space of the accommodating portion 20 and the accommodation space 20a communicate with each other. The opening 22a penetrates the bottom wall 22 so that the external space of the accommodating portion 20 and the accommodation space 20a communicate with each other. A plurality of openings 21a and 22a are provided in each of the side walls 21 and the bottom wall 22 in a mesh-like or lattice-like pattern, for example. Through the openings 21a and 22a, the water in the water area 2 can penetrate into the accommodation space 20a. Through the openings 21a and 22a, the water that has penetrated into the accommodation space 20a can flow out to the outside of the accommodating portion 20.

[0025] In the accommodation space 20a, a gap 20b is formed between adjacent base materials 10 or between the base material 10 and the side wall 21 or the bottom wall 22. For example, there is a gap 20b that communicates from above to below among the plurality of base materials 10 accommodated within the accommodation space 20a of the accommodating portion 20.

[0026] The plant body 30 is planted on a plurality of base materials 10 accommodated in the accommodation space 20a of the accommodation part 20. The number of plant bodies 30 planted with respect to the accommodation part 20 may be one or a plurality. For example, a part (leaf) of the plant body 30 is exposed above the water. Thereby, the plant body 30 can exhibit transpiration, transpire the water in the water area 2 into the atmosphere, and reduce the water volume of the water area 2. The plant body 30 is, for example, an aquatic plant having resistance to sewage. The plant body 30 is, for example, an aquatic plant in which rhizomes or roots grow in a mesh shape. Hereinafter, the rhizomes and roots may be collectively described as "roots" in some cases. The plant body 30 is, for example, a pumping plant, a terrestrial plant, a floating plant, a floating-leaved plant, or the like. When the plant body 30 is a pumping plant, the plant body 30 is, for example, a sweet flag and a reed. The plant body 30 may also be a plant used for the purification (phytoremediation) of metals or harmful chemicals. Note that the plant body 30 may be a plant that does not have resistance to sewage depending on the water quality of the water area 2.

[0027] The roots of the plant body 30 take root in the gap 20b between the plurality of base materials 10. By entering and growing in the gap 20b, the roots of the plant body 30 are stretched in a mesh shape within the accommodation space 20a. A part of the roots of the plant body 30 is in contact with the plurality of base materials 10 in the gap 20b. The roots of the plant body 30 are in contact, for example, by entangling with the plurality of base materials 10. The roots of the plant body 30 may protrude outside the accommodation part 20 through the gap 20b, the openings of the mesh member 23, and the openings 21a and 22a in this order. The plant body 30 grows by absorbing moisture, for example, by spreading its roots in the flooded gap 20b and outside the accommodation part 20.

[0028] The floating part 40 is a member for floating the accommodation part 20 in the water area 2. When the floating artificial wetland 1 is installed in the water area 2, the floating part 40 floats the accommodation part 20 so that, for example, the leaves of the plant body 30 are exposed from the water surface and most of the accommodation space 20a is located below the water surface. The floating part 40 is provided detachably with respect to the accommodation part 20, for example.

[0029] The floating body part 40 is adjusted so that the housing part 20 floats at an appropriate position in the water of the water area 2 in the vertical direction (Z direction). The floating body part 40 has, for example, a cylindrical shape. The floating body part 40 is made of a material containing, for example, vinyl chloride or foamed resin. The floating body part 40 is, for example, a vinyl chloride pipe. In the present embodiment, the floating artificial wetland 1 includes a plurality of floating body parts 40. For example, four floating body parts 40 are respectively provided on the four side walls 21. Each floating body part 40 is provided, for example, along the upper end edge of the side wall 21 on the outer surface of the side wall 21, and is attached to the side wall 21 by a connecting tool (not shown) such as a binding band or wire. Note that the number, material, weight, shape, and size of the floating body part 40 are not limited. The number, material, weight, size, etc. of the floating body part 40 are appropriately set according to the weight of the entire floating artificial wetland 1.

[0030] Next, a method for installing the floating artificial wetland 1 will be described. First, a plurality of base materials 10 are accommodated (filled) in the accommodation space 20a of the housing part 20. Subsequently, the plant bodies 30 are planted on the plurality of base materials 10. Subsequently, the floating body part 40 is attached to the housing part 20. Subsequently, the floating artificial wetland 1 is transported to the water area 2 and installed by floating the floating artificial wetland 1 in the water area 2.

[0031] [Function of the floating artificial wetland] Next, the function of the floating artificial wetland 1 installed in the water area 2 will be described. When the floating artificial wetland 1 is floated in the water area 2, the water in the water area 2 flows into the accommodation space 20a through the openings 21a and 22a of the housing part 20. As a result, most of the plurality of base materials 10 are flooded, and the water in the water area 2 also enters the gap 20b. Note that the water in the water area 2 may flow into the accommodation space 20a through the opening above the housing part 20. Since the roots of the plant bodies 30 are mesh-like and are rooted (entered) in the gap 20b, when the roots of the plant bodies 30 come into contact with the water in the water area 2, the plant bodies 30 absorb moisture and further grow.

[0032] An environment called the rhizosphere is formed around the roots of the plant body 30. The rhizosphere is an area affected by the roots and is an area with high microbial activity around the roots. The rhizosphere is formed by compounds released from the roots and microorganisms. Various types of microorganisms can reproduce in response to the specific environment of this rhizosphere (rhizosphere effect). Due to the rhizosphere effect, many microorganisms accumulate around the roots. Many of the accumulated microorganisms are retained on the surface of each base material 10, the surface of the roots of the plant body 30, and the gap 20b. Depending on the accumulated microorganisms, for example, a biofilm may be formed on the base material 10.

[0033] The microorganisms accumulated in the accommodation space 20a have a water purification effect. The microorganisms include those having a reducing effect on refractory organic substances. Examples of such microorganisms include the classes Alphaproteobacteria, Gammaproteobacteria, and Betaproteobacteria. The microorganisms accumulated in the accommodation space 20a include those having a reducing effect on refractory organic substances, organic carbon, and nitrogen. In addition, the microorganisms accumulated in the accommodation space 20a include those having a biofilm-forming effect. Therefore, the water quality of the water in the water area 2 flowing into the accommodation space 20a is improved by the microorganisms accumulated in the accommodation space 20a.

[0034] The water whose water quality has been improved by the microorganisms flows out from the inside of the accommodation space 20a to the outside of the accommodation part 20 by the water flow generated in the water area 2. When the floating artificial wetland 1 is floatingly installed in the water area 2, the water in the water area 2 continuously flows into and out of the accommodation part 20 by the water flow, so the water quality is improved by the water purification effect of the microorganisms in the accommodation space 20a. By installing a plurality of floating artificial wetlands 1 in the water area 2, a stronger water purification effect can be exerted compared to the case where one floating artificial wetland 1 is installed.

[0035] [Effect of Floating Artificial Wetland] Next, with reference to FIGS. 3(a) to 6, the effects of the floating artificial wetland will be described. Hereinafter, for the examples and comparative examples, the configuration of the floating artificial wetland not particularly described shall be the same as that of the floating artificial wetland 1 in the above-described embodiment.

[0036] [Changes in the residual rates of recalcitrant organic substances, nitrogen, and organic nitrogen] The changes in the residual rates of organic carbon, nitrogen, and organic nitrogen with respect to the measurement start date and the number of elapsed days were compared between the water when the floating artificial wetland was introduced into the water area (Example 1) and the water when the floating artificial wetland was not introduced into the water area (Comparative Example 1). Organic carbon refers to total organic carbon (TOC). Nitrogen refers to total nitrogen (TN). Organic nitrogen refers to Org-N (Organic Nitrogen).

[0037] In Example 1, a floating artificial wetland having the same configuration as the floating artificial wetland 1 of the above-described embodiment was used, and it is a purification system installed in an aquarium. Foamed glass was used as the base material. Sixteen cattails were planted as plants in the accommodation part. The accommodation part is a cage with a width of 0.18 m, a depth of 0.23 m, and a height of 0.1 m, and is open upward. The side walls and bottom of the accommodation part are lattice-shaped. Each opening is rectangular, and the size of each opening is 2.5 cm in length and 2.5 cm in width. The aquarium is an example of water area 2. The aquarium is a container with a width of 0.27 m, a depth of 0.32 m, and a height of 0.14 m, and is open upward. At the start of the experiment, 6 L of water (aqueous solution) adjusted by adding humic acid to tap water so that the concentration of humic acid was 0.8 g / L was stored in the aquarium as an example of the water in water area 2. In Example 1, one floating artificial wetland was provided for one aquarium.

[0038] Comparative Example 1 is a control system without a floating artificial wetland installed. In Comparative Example 1, the same water tank and the same water as in Example 1 above were prepared. Samples were taken from the water in the water tank to which Example 1 was applied and the water in the water tank to which Comparative Example 1 was applied every day after the start date of measurement, and the residual rate of organic carbon, the residual rate of nitrogen, and the residual rate of organic nitrogen for each of the samples were calculated respectively. The start date of measurement in Example 1 is the day when water was stored in the water tank and the floating artificial wetland was installed in the water tank. The start date of measurement in Comparative Example 1 is the day when water was stored in the water tank. Each residual rate refers to the ratio (percentage) of the total amount (mg) of each compound measured in each sample on the measurement date to the total amount (mg) of each compound measured in each sample at the start date of measurement. Hereinafter, the sample of the water in the water tank to which the example was applied may be described as "water according to the example", and the sample of the water in the water tank to which the comparative example was applied may be described as "water according to the comparative example". Tap water in the same amount as the amount of water released from the water tank by evapotranspiration was appropriately added to the water tank of Example 1 and the water tank of Comparative Example 1. Note that the water in each water tank was blackish brown on the start date of measurement.

[0039] Figure 3(a) is a graph showing the change in the residual rate of organic carbon in the water according to Example 1 and the water according to Comparative Example 1. The horizontal axis of the graph shown in Figure 3(a) indicates the number of days elapsed from the start date of measurement (days), and the vertical axis of the graph indicates the residual rate of organic carbon (%). Figure 3(b) is a graph showing the change in the residual rate of nitrogen in the water according to Example 1 and the water according to Comparative Example 1. The horizontal axis of the graph shown in Figure 3(b) indicates the number of days elapsed from the start date of measurement (days), and the vertical axis of the graph indicates the residual rate of nitrogen (%). Figure 3(c) is a graph showing the change in the residual rate of organic nitrogen in the water according to Example 1 and the water according to Comparative Example 1. The horizontal axis of the graph shown in Figure 3(c) indicates the number of days elapsed from the start date of measurement (days), and the vertical axis of the graph indicates the residual rate of organic nitrogen (%).

[0040] As shown in FIGS. 3(a), 3(b), and 3(c), in Comparative Example 1, the residual ratios of organic carbon, nitrogen, and organic nitrogen did not change even after the number of days had elapsed since the start of measurement. In contrast, in Example 1, as the number of days elapsed since the start of measurement, the residual ratios of organic carbon, nitrogen, and organic nitrogen all decreased. Humic acid is a high-molecular organic substance containing carbon atoms and nitrogen atoms, and the organic substances contained in the water in the water tank are only humic acid. Therefore, it was suggested that the floating artificial wetland decomposed humic acid, which is a refractory organic substance in water, and then reduced organic carbon, nitrogen, and organic nitrogen.

[0041] FIG. 4(a) is an image showing the water according to Example 1 and the water according to Comparative Example 1 32 days after the start of measurement. FIG. 4(b) is an image showing the water according to Example 1 and the water according to Comparative Example 1 40 days after the start of measurement. FIG. 4(c) is an image showing the water according to Example 1 and the water according to Comparative Example 1 52 days after the start of measurement. FIG. 4(d) is an image showing the water according to Example 1 and the water according to Comparative Example 1 56 days after the start of measurement.

[0042] As shown in FIGS. 4(a) to 4(d), the color of the water according to Comparative Example 1 did not change even after the number of days had elapsed since the start of measurement, and it had an opaque blackish-brown color. In contrast, the color of the water according to Example 1 became lighter and transparent as the number of days elapsed since the start of measurement. Since the tap water before the addition of humic acid is transparent and the water after the addition of humic acid exhibits a blackish-brown color, the fact that the color of the water in the water tank has become lighter and transparent from blackish-brown is considered to indicate that the amount of humic acid contained in the water in the water tank has decreased. Therefore, it was suggested that the floating artificial wetland reduced the humic acid contained in the water in the water tank.

[0043] [Transition of Cover Ratio of Floating Artificial Wetland and Concentration of Refractory Organic Substances] For Examples 2 to 12 with different proportions of floating artificial wetlands in the water area, the changes in COD over time were compared. COD refers to Chemical Oxygen Demand (chemical oxygen demand), and may be simply described as "concentration" below.

[0044] Examples 2 to 12 are simulation examples assuming cases where floating artificial wetlands are applied to the target retention pond in different areas. For each of Examples 2 to 12, under the following simulation conditions, the COD of the retention pond is calculated every day from the time when the initial value of COD is set (initial setting date). For example, a simulation for a period of 800 days is performed. Examples 2 to 12 differ in the proportion of the floating artificial wetland in the water surface area of the retention pond (hereinafter may be described as the coverage rate). The coverage rates of Examples 2 to 12 are 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100% respectively. The coverage rate is changed by adjusting the number or area of the floating artificial wetlands installed in the retention pond.

[0045] The retention ponds targeted for simulation in Examples 2 to 12 are areas for storing leachate. The retention pond is an example of Water Area 2 virtually set based on an actual retention pond. The water surface area of the retention pond is 28985 m 2 , the water depth is 3 m, and the water volume is 86955 m 3 is set. It is assumed that 46298 m 3 of leachate flows into the retention pond annually. The hydraulic retention time (HRT) of the retention pond is set to 2 years. The inflow concentration (COD) of the leachate is set to 1500 mg / L, and the proportion of humic acid per COD is set to 40%. The initial value of COD in the retention pond is set to 600 mg / L. In this simulation, it is set to calculate the COD of the retention pond when each of Examples 2 to 12 is applied using a predetermined reaction rate derived based on Example 1 above.

[0046] Fig. 5(a) is a graph showing the relationship between the number of days elapsed and COD for each coverage rate of the floating artificial wetland with respect to the water area. The horizontal axis of the graph shown in Fig. 5(a) represents the number of days elapsed (days), and the vertical axis represents the concentration (mg / L) calculated by simulation. The number of days elapsed in this simulation is the number of days elapsed from the initial setting date in the simulation. Fig. 5(b) is a graph showing the relationship between the coverage rate of the floating artificial wetland with respect to the water area and the required treatment time (days). The horizontal axis of the graph shown in Fig. 5(b) represents the coverage rate of the floating artificial wetland set in the simulation, and the vertical axis represents the required treatment time (days). The required treatment time will be described later.

[0047] As shown by the dashed line in Fig. 5(a), in this simulation, the target concentration (COD) when discharging treated water out of the storage pond as treated water was set to 120 mg / L. Treated water is water in which the COD has become less than or equal to the target concentration by purifying the leachate. Since the hydraulic retention time of the storage pond was set to 2 years, it is sufficient if the treated water can be discharged out of the storage pond before the number of days elapsed exceeds about 730 days. The required treatment time on the horizontal axis shown in Fig. 5(b) is the number of days required for the water according to Examples 2 to 12 to reach the target concentration from the above initial setting date. In Fig. 5(b), Examples 3 to 12 are plotted based on the required treatment times of Examples 3 to 12 shown in Fig. 5(a).

[0048] As shown in FIGS. 5(a) and 5(b), the higher the coverage rate, the shorter the required processing time. When the coverage rate is 10% or more, the COD of the water in the storage pond becomes less than the target concentration before the number of elapsed days exceeds about 600 days. Therefore, in this simulation, if a floating artificial wetland is installed so that the coverage rate of the floating artificial wetland is 10% or more, the leachate in the storage pond can be appropriately purified and changed into treated water and discharged outside the storage pond. For example, in order to make the COD of the water in the storage pond reach the target concentration within one year, a floating artificial wetland may be installed so that the coverage rate of the floating artificial wetland is 20% or more. As shown in FIG. 5(a), after a sufficient number of days have elapsed, the COD becomes almost constant when the water purification effect of the floating artificial wetland and the pollution by the water flowing into the storage pond reach an equilibrium state. After a sufficient number of days have elapsed, the higher the coverage rate of the floating artificial wetland, the lower the COD of the water in the storage pond can be maintained.

[0049] From these facts, it can be understood that by appropriately adjusting the coverage rate of the floating artificial wetland according to the target concentration and the hydraulic retention time of the storage pond, the concentration can be made below the target concentration.

[0050] [Transition of cumulative removal amount of hardly decomposable organic substances] The influence of the configuration of the floating artificial wetland on the removal amount of hardly decomposable organic substances was verified. In this verification, Example 13 and Comparative Examples 2 and 3 were used. In Example 13, foamed glass was used as the base material. Two strains of Miscanthus sacchariflorus were planted as plants in the accommodation part. As a container for accommodating the base material, a pot with a diameter of 11 cm and a height of 19 cm was used. The pot is a container capable of storing liquid and is different from the accommodation part 20 having an opening. The same type of pot was also used in the comparative examples. At the start of the experiment, a humic acid solution was added to the pots of Example 13 and Comparative Examples 2 and 3. Every 3 days (1 batch), the entire amount of water in the pot was discarded, and a replacement process of supplying a new humic acid solution into the pot was performed. The replacement process was repeated a total of 8 times (8 batches). The concentration of the humic acid solution supplied during the replacement process was different for each batch, and the concentration range was 0.25 g / L or more and 0.8 g / L or less.

[0051] Comparative Example 2 differs from Example 13 in that only the plant body is accommodated in the pot instead of a plurality of base materials and the plant body. Comparative Example 3 differs from Example 13 in that only a plurality of base materials are accommodated in the pot instead of a plurality of base materials and the plant body. That is, in Comparative Example 3, no plant body is planted.

[0052] Samples (hereinafter, may be referred to as "samples for Example 13", "samples for Comparative Example 2", and "samples for Comparative Example 3") were collected from the water in the water tank to which Example 13 and Comparative Examples 2 and 3 were applied every time each batch ended from the measurement start date, and the total amount of persistent organic substances in each of the samples was measured. The measurement start date is the date when each of Example 13 and Comparative Examples 2 and 3 was installed in each pot. FIG. 6 is a graph showing a comparison of the relative cumulative removal amounts of persistent organic substances according to Example 13 and Comparative Examples 2 and 3. The vertical axis of the graph shown in FIG. 6 indicates the relative cumulative removal amount of persistent organic substances. The organic carbon removal amount was adopted as an index of the removal amount of persistent organic substances. The cumulative removal amount of persistent organic substances is the sum of the values obtained by subtracting the total amount of persistent organic substances in each sample at the end of each batch from the total amount of persistent organic substances in each sample at the measurement start date of each batch. The relative cumulative removal amount was calculated with the cumulative removal amount of Comparative Example 2 (only the gamma) as 1 and the cumulative removal amounts of Comparative Example 3 (only the base material) and the examples as relative values.

[0053] As shown in FIG. 6, the removal amount of Example 13 was about 10 times the removal amount of Comparative Example 2 and about 4 times the removal amount of Comparative Example 3. From this, it was suggested that the reduction effect of persistent organic substances by only the absorption / adsorption action of the plant body or only the adsorption action of the base material is small, but the reduction effect is significantly enhanced by the plant roots being attached to a plurality of base materials.

[0054] As a result of gene analysis targeting the 16S rRNA gene, it was confirmed that the microorganisms accumulated in the water tank to which Example 13 was applied were composed of a microbial community different from that of the comparative examples. For example, in the sample for Example 13, the genus Pseudomonas was the most dominant. The proportion of the microorganisms belonging to the genus Pseudomonas in the sample for Example 13 was about 1000 times higher than that in the sample for Comparative Example 2 and about 4 times higher than that in the sample for Comparative Example 3. The microorganisms belonging to the genus Pseudomonas contribute to the decomposition of polycyclic aromatic hydrocarbons, biphenyl, and PCB, etc., the production of biopolymers, and nitrogen circulation, etc., and have the ability to form biofilms.

[0055] For example, in the sample for Example 13, the genus Steroidobacter was dominant. The proportion of the microorganisms belonging to the genus Steroidobacter in the sample for Example 13 was about 2 times higher than that in the sample for Comparative Example 2. In the sample for Comparative Example 3, the microorganism was not detected. The microorganisms belonging to the genus Steroidobacter are known to contribute to the decomposition of steroid hormones such as estradiol and testosterone and have a denitrification function. Furthermore, in the sample for Example 13, the genera Georgfuchsia, Chryseolinea, and Caulobacter were dominant. The microorganisms belonging to these genera have been reported to contribute to the decomposition of aromatic compounds and have a denitrification function and the ability to form biofilms. Therefore, it was suggested that, unlike the structure composed only of plant bodies and the structure composed only of base materials, since the roots of the plant bodies are colonized in a plurality of base materials, the floating artificial wetland accumulates a large amount of the above microorganisms, and the reduction effect of hardly decomposable organic substances is remarkably enhanced.

[0056] [Summary of the effects] As described above, the roots of the plant bodies 30 in the floating artificial wetland 1 take root in the gaps 20b defined by the plurality of base materials 10. As a result, due to the rhizosphere effect, a large number and a large variety of microorganisms accumulate not only around the roots of the plant bodies 30 but also in the gaps 20b between the plurality of base materials 10 and the plurality of base materials 10. It is presumed that the number of microorganisms accumulated in the floating artificial wetland 1 and contributing to the reduction of nutrients such as nitrogen and phosphorus, the reduction of organic substances, and the reduction of hardly decomposable organic substances is larger than the number of microorganisms accumulated in the conventional vegetation floating islands. Also, it is presumed that the types of the microorganisms accumulated in the floating artificial wetland 1 are more than the types of the microorganisms accumulated in the conventional vegetation floating islands. With the accumulation of many microorganisms having a water purification effect including the reduction effect of hardly decomposable organic substances, the floating artificial wetland 1 can exhibit a higher water purification effect. Also, the floating artificial wetland 1 is installed so as to float in the water area 2. For this reason, it is not necessary to separately prepare a large installation place other than the water area 2 like an artificial wetland provided on land, and large-scale construction is not required. Therefore, the floating artificial wetland 1 can be more easily installed than an artificial wetland installed on land. As described above, this floating artificial wetland 1 can facilitate installation and exhibit a higher water purification effect.

[0057] The microorganisms accumulated due to the rhizosphere effect can enter the porous base material 10. For this reason, the floating artificial wetland 1 can hold more microorganisms than a floating artificial wetland having a non-porous base material, so the floating artificial wetland 1 can exhibit an even higher water purification effect.

[0058] When the water in the water area 2 enters the accommodating portion 20 through the openings 21a and 22a provided in the accommodating portion 20, the plurality of base materials 10 in the accommodation space 20a are flooded. Thus, water can be supplied into the accommodating portion 20 only by floating the floating artificial wetland 1 in the water area 2. Therefore, since a configuration for supplying the water in the water area 2 from the opening above the accommodating portion 20 is unnecessary, the structure of the floating artificial wetland 1 can be simplified.

[0059] For example, just with a plurality of base materials 10, a housing part 20, and a plant body 30, it may not be possible to float the floating artificial wetland 1 in the water area 2 due to their weight. Since the floating artificial wetland 1 is provided with a floating body part 40, even if the plurality of base materials 10, the housing part 20, and the plant body 30 are heavy, the floating artificial wetland 1 can be floated in the water area 2. Therefore, the degree of freedom in the configuration of the plurality of base materials 10, the housing part 20, and the plant body 30 can be increased.

[0060] For example, as the plant body 30 grows, the weight of the floating artificial wetland 1 may change. In such a case, it may be necessary to adjust the floating position (floating height) of the floating artificial wetland 1. In the floating artificial wetland 1, since the floating body part 40 can be attached to and detached from the housing part 20, it can be replaced with an appropriate floating body part 40 according to the weight of the floating artificial wetland 1. Therefore, it is possible to flexibly respond to changes in the weight of the floating artificial wetland 1.

[0061] A part (leaves) of the plant body 30 is exposed above the water. In this case, the part (leaves) of the plant body 30 that is exposed above the water can exert a transpiration effect. Therefore, the amount of water in the water area 2 can be reduced by the transpiration effect of the plant body 30.

[0062] Since the plant body 30 is an aquatic plant having resistance to sewage, the floating artificial wetland 1 can be installed in a polluted water area and the polluted water area can be purified.

[0063] Hereinafter, the effects of the floating artificial wetland 1 compared with the prior art will be described. As prior arts using plant bodies, a vegetated floating island and an artificial wetland can be cited. Also, as technologies for removing hardly decomposable organic substances, a coagulation sedimentation device and an activated carbon purification device can be cited. The roots of the plant bodies of the conventional vegetated floating islands only penetrate into the holes provided in the base, and the roots of the plant bodies cannot sufficiently take root in the base. Since it has been found that microorganisms capable of reducing hardly decomposable organic substances are retained in the base where the roots of the plant bodies have sufficiently taken root, it is considered that the conventional vegetated floating islands cannot retain microorganisms capable of reducing hardly decomposable organic substances.

[0064] When an artificial wetland is installed on land, it is necessary to secure land other than water areas for installing the artificial wetland. Further, since it is necessary to manufacture a storage section that does not leak water that has not been purified, and to manufacture a supply section that supplies water from above the storage section to the storage section, a lot of man-hours are required. When an artificial wetland is installed on land, depending on the rainfall intensity, the water level in the storage section may rise rapidly, so there is a risk that the water in the unpurified storage section will overflow. In addition, since pumping plants are used as plants in the artificial wetland, the artificial wetland cannot be installed in places with high water levels. As described above, the artificial wetland can only be installed on land or on the shore with a low water level. That is, there are restrictions on the application destination of the artificial wetland.

[0065] In the conventional coagulation sedimentation apparatus, costs are involved in power, chemicals, and sludge disposal. In addition, a lot of man-hours are required for manufacturing each treatment tank related to the coagulation sedimentation apparatus, and it is necessary to secure land other than water areas for installing the coagulation sedimentation apparatus. Similarly, in the conventional activated carbon purification apparatus, costs are involved in the purchase of power and activated carbon, and the disposal of used activated carbon. In addition, a lot of man-hours are required for manufacturing the activated carbon reaction tank, and it is necessary to secure land other than water areas for installing the activated carbon purification apparatus.

[0066] In contrast to these conventional technologies, the floating artificial wetland 1 can hold more microorganisms having a water purification effect including reduction of hardly decomposable organic substances by the rhizosphere effect on the surfaces of the plurality of base materials 10, the surfaces of the roots of the plants 30, and the gaps 20b. Further, since the floating artificial wetland 1 is installed by floating in the water area 2, it is less restricted by the application destination, and can appropriately exhibit the water purification effect on the water in the water area 2. Even when the water level of the water area 2 drops and the floating artificial wetland 1 touches the bottom, for example, when a plurality of base materials 10 are flooded and the water in the water area 2 also enters the gaps 20b, the water purification effect can be exhibited.

[0067] The floating artificial wetland 1 can be manufactured with a simple structure including a plurality of base materials 10, a housing part 20, plant bodies 30, and a floating part 40, so it can be installed with less man-hours compared to the prior art. Since the housing part 20 has openings 21a and 22a, unlike conventional artificial wetlands, the floating artificial wetland 1 does not need to have a facility for supplying water from the water area 2 from above, so it can be installed with less man-hours and can exhibit a water purification effect at a low cost.

[0068] [Modification Example] As described above, the embodiments of the present disclosure have been described, but the present disclosure is not limited to the above embodiments. For example, each base material 10 may not be porous. Even in this case, since the microorganisms propagated by the rhizosphere effect are retained on the surfaces of the respective base materials 10, the gaps 20b, and the surfaces of the roots of the plant bodies 30, the floating artificial wetland 1 has a high water purification effect.

[0069] In the housing part 20, either of the openings 21a and 22a may not be provided. In this case, water from the water area 2 may be allowed to flow into the accommodation space 20a through the opening provided in the housing part 20 and the upper opening. Neither of the openings 21a and 22a may be provided in the housing part 20. In this case, water from the water area 2 may be allowed to flow into the accommodation space 20a through the upper opening provided in the housing part 20. By appropriately changing the material or size of the floating part 40, the floating height of the floating artificial wetland 1 may be adjusted so that the upper opening provided in the housing part 20 is located below the water surface of the water area 2. The housing part 20 may not have the net-like member 23. In this case, by appropriately changing the sizes of the openings 21a and 22a, the base materials 10 may be prevented from leaking outside the housing part 20. The sizes of the openings 21a and 22a are, for example, smaller than the size of the base materials 10. Also, the net-like member 23 may be disposed outside the accommodation space 20a. In this case, the net-like member 23 may be fixed to the outer surfaces of, for example, the four side walls 21 and the bottom wall 22.

[0070] The floating artificial wetland 1 may not be provided with the floating part 40. In this case, the accommodating part 20 may be configured to accommodate the plurality of base materials 10 and float on the water in the water area 2 even when the plant bodies 30 are planted. The accommodating part 20 may be made of a material having a specific gravity smaller than that of the water in the water area 2, for example. The floating part 40 may be detachably provided with respect to the accommodating part 20. In this case, for example, the accommodating part 20 provided with the floating part 40 corresponding to the weights of the plurality of base materials 10 and the plant bodies 30 is selected.

[0071] The plant bodies 30 may not be exposed above the water surface. In this case, aquatic plants capable of growing underwater are appropriately selected as the plant bodies 30. For example, the floating artificial wetland 1 may be introduced into a water area that is not a polluted water area. In this case, the plant bodies 30 may not have resistance to sewage.

[0072] In the water area 2, the entire floating artificial wetland 1 may be located below the water surface and float from the water bottom. When the floating artificial wetland 1 is floated in the water area 2, at least a part of the plurality of base materials 10 may be immersed in water. For example, only a part of the plurality of base materials 10 may be immersed in water.

Explanation of reference numerals

[0073] 1... Floating artificial wetland, 2... Water area, 10... Base material, 20... Accommodating part, 20a... Accommodating space, 20b... Gap, 21... Side wall, 21a, 22a... Opening, 22... Bottom wall, 23... Mesh member, 30... Plant body, 40... Floating part.

Claims

Claim 1 A floating artificial wetland installed by floating in a water area, a plurality of granular base materials having a specific gravity smaller than that of the water in the water area and being porous, a housing portion for housing the plurality of base materials, plants planted in the plurality of base materials, comprising: the roots of the plants take root in the gaps between the plurality of base materials, the housing portion has side walls and a bottom wall, openings through which the water in the water area can enter the housing space defined by the housing portion are provided in the side walls and the bottom wall of the housing portion, the plants are aquatic plants having resistance to sewage, a floating artificial wetland. Claim 2 The floating artificial wetland according to claim 1, further comprising a floating portion for floating the housing portion in the water area. Claim 3 The floating artificial wetland according to claim 2, wherein the floating portion is detachably provided on the housing portion. Claim 4 The floating artificial wetland according to claim 2 or 3, wherein the floating portion is arranged such that most of the housing space is located below the water surface of the water area. Claim 5 In the floating artificial wetland according to any one of claims 1 to 4, a part of the plants is exposed above the water surface.

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