JP2006346554A - System and method for cleaning water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method for cleaning water, in each of which the water of a water zone of a river, a lake, a marsh, a basin, an inland sea or the like is cleaned to obtain treated water of low phosphorus concentration. <P>SOLUTION: The system and the method for cleaning water each comprise a direct cleaning means and an ion adsorbing means packed with a porous molding. The porous molding comprises an organic polymeric resin and an inorganic ion adsorbent and has a communicative pore opened to the outside surface and a void in a fibril forming the communicative pore. At least a part of the void is opened to the surface of the fibril. The inorganic ion adsorbent is deposited on the outside surface of the fibril and on the surface of the internal void. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a water purification system and a water purification method for purifying water areas such as rivers, lakes, inner bays, and inland seas. Furthermore, the present invention relates to a water purification system and a water purification method having a low phosphorus concentration in treated water.

Although rivers, lakes and marine areas in Japan have improved from a certain point of time, there are still many areas where improvement has not been observed. In particular, pollution of closed water areas such as lakes, inner bays, and inland seas and urban small and medium rivers is remarkable. The cause of these water pollution is mainly untreated domestic wastewater, but depending on the water area, unregulated wastewater such as livestock and small-scale establishments may occupy a significant proportion. It goes without saying that the source control is the most effective, but it is almost impossible to control the water quality of household household wastewater, and it is technically possible to fundamentally control non-specific pollution sources. It is extremely difficult. For this reason, a direct purification method is being studied in order to purify the water quality of water areas where pollution is advancing.
Edited by Ryuichi Sudo, Biology for Water Environment Conservation, Industrial Water Research Committee, 2004

The direct purification method has a problem that the phosphorus concentration in the treated water cannot be sufficiently reduced.
An object of the present invention is to provide a water purification system and a water purification method for purifying water areas such as rivers, lakes, inner bays, and inland seas, and in particular, a water purification system and a water purification method with low phosphorus concentration in treated water.

In order to solve the above-mentioned problems, the present inventor has found a water purification system and a water purification method which are newly composed of a direct purification means and an ion adsorption means filled with a porous molded body, and have made the present invention.
That is, the present invention is as follows.
(1) A water purification system comprising a direct purification means and an ion adsorption means filled with a porous molded body, wherein the porous molded body comprises an organic polymer resin and an inorganic ion adsorbent. A pore formed inside the fibril forming the communication hole, and at least a part of the void is open on the surface of the fibril, Water purification system which is a porous molded body in which an inorganic ion adsorbent is supported on the outer surface and the inner void surface

(2) The water purification system according to (1), wherein the direct purification means is an aquatic plant planting method.
(3) The water purification system according to (1) or (2), wherein the communication hole is a porous molded body having a maximum pore diameter layer near the surface of the molded body.
(4) The porous organic polymer resin contains at least one selected from the group consisting of ethylene vinyl alcohol copolymer (EVOH), polyacrylonitrile (PAN), polysulfone (PS), and polyvinylidene fluoride (PVDF). The water purification system as described in any one of (1)-(3) which is a property molded object.

(5) The water purification system according to any one of (1) to (4), wherein the inorganic ion adsorbent contains at least one metal oxide represented by the following formula (I).

_{MN x O n · mH 2 O} (I)
(Wherein x is 0 to 3, n is 1 to 4, m is 0 to 6, and M and N are Ti, Zr, Sn, Sc, Y, La, Ce, Pr, Nd, Sm, Eu. Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Si, Cr, Co, Ga, Fe, Mn, Ni, V, Ge, Nb and Ta are metal elements selected from the group Are different from each other.)

(6) The metal oxide represented by the formula (I) is one or a mixture of two or more selected from any of the following groups (a) to (c) ( The water purification system as described in 5).
(A) hydrated titanium oxide, hydrated zirconium oxide, hydrated tin oxide, hydrated cerium oxide, hydrated lanthanum oxide, and hydrated yttrium oxide (b) consisting of titanium, zirconium, tin, cerium, lanthanum, and yttrium A composite metal oxide of a metal element selected from the group and a metal element selected from the group consisting of aluminum, silicon, and iron (c) activated alumina

(7) In a water purification method including a direct purification step and an ion adsorption step filled with a porous molded body, the porous molded body includes an organic polymer resin and an inorganic ion adsorbent, and has an opening on the outer surface. A porous molded body having a communication hole that has a void inside the fibril forming the communication hole, and at least a part of the void is open on the surface of the fibril, and the outside of the fibril. The present invention relates to a method for purifying water, which is a porous molded body in which an inorganic ion adsorbent is supported on the surface and the internal void surface.

The water purification system and the water purification method of the present invention relate to a water purification system and a water purification method for purifying water areas such as rivers, lakes, inner bays, and inland seas, and have an effect of low phosphorus concentration in treated water.

The present invention will be specifically described below.
The present invention relates to a water purification system comprising a direct purification means, and an ion adsorption means filled with a porous molded body, and a method thereof.
The direct purification means of the present invention is not particularly limited, but is roughly divided into a direct method for purifying in situ rivers and ponds and a separation method for purifying polluted water in a reaction tank that is pumped up into an apparatus. The As direct methods, aeration method, water dilution method for purification, subsurface purification method, laminar flow purification method, sedimentation pond method, low mud dredging method, algae / aquatic plant recovery method, contact material filled water channel purification method, activated carbon purification method, aquatic The plant planting method etc. are mentioned.

  Examples of the separation method include a gravel contact oxidation method, a sand filtration method, and a coagulation sedimentation method. The separation method requires a very large site or an advanced facility, so the direct method is preferable. In particular, the aquatic plant planting method is more preferable because it can maintain a rich ecosystem and has a low environmental load. Examples of aquatic plants include extraction plants, floating plants, submerged plants, and floating leaf plants, but extraction plants are preferred because of their advantages such as thriving fertility, densely populated communities, low moisture, and reusability. . Examples of water extraction plants include rush, rice, Dutch glass, cattail, chickpea, pakbun, papyrus, makomo, and Yoshi. In particular, reed is more preferable because it can form a wetland having a biomass conversion action of several stages.

The ion adsorption means filled with the porous molded body of the present invention is mainly a means for reducing the phosphorus concentration in the treated water. Furthermore, phosphorus useful as a resource can be recovered.
The present invention is a water purification system comprising a direct purification step and an ion adsorption step filled with a porous molded body, wherein the porous molded body comprises an organic polymer resin and an inorganic ion adsorbent. A porous molded body having a communication hole opening on the surface, the fibril forming the communication hole has a void inside, and at least a part of the void is open on the surface of the fibril, A water purification system and a water purification method, which are porous molded bodies in which an inorganic ion adsorbent is supported on the outer surface of a fibril and the inner void surface. The ion adsorption step is preferably performed after the ion adsorption step from the viewpoint of ion adsorption efficiency.

The porous molded body of the present invention will be described in detail below.
First, the structure of the molded body of the present invention will be described.
The molded body of the present invention has a communication structure and a porous structure. Furthermore, there is no skin layer on the outer surface, and the surface has excellent opening properties. Further, there is a void inside the fibril forming the communication hole, and at least a part of the void is opened on the fibril surface.

The outer surface aperture ratio of the molded article of the present invention refers to the ratio of the sum of the aperture areas of all the holes in the area of the field of view when the surface is observed with a scanning electron microscope. In the present invention, the surface of the molded body was observed at a magnification of 10,000 to actually measure the outer surface opening ratio. The range of the surface opening ratio is preferably 10 to 90%, and particularly preferably 15 to 80%. If it is less than 10%, the diffusion rate of the substance to be adsorbed, such as phosphorus, into the molded body will be slow, whereas if it exceeds 90%, the molded body will have insufficient strength and it will be difficult to realize a molded article with excellent chemical strength. It is.
The outer surface opening diameter of the molded body of the present invention is determined by observing the surface with a scanning electron microscope. When the hole is circular, the diameter is used. When the hole is not circular, the equivalent circle diameter of a circle having the same area is used. A preferable range of the surface opening diameter is O.005 μm to 100 μm, and particularly preferably O.01 μm to 50 μm. If it is less than O.005 μm, the diffusion rate of the substance to be adsorbed such as phosphorus into the molded body tends to be slow, whereas if it exceeds 100 μm, the strength of the molded body tends to be insufficient.

  The molded body of the present invention has voids in the fibrils forming the communication holes, and at least a part of the voids are opened on the surface of the fibrils. The inorganic ion adsorbent is supported on the outer surface of the fibril and the void surface inside the fibril. Since the fibril itself is also porous, an inorganic ion adsorbent that is an adsorption substrate embedded inside can also come into contact with an adsorption target substance called phosphorus, and can effectively function as an adsorbent.

  In the porous molded body of the present invention, since the portion where the adsorption substrate is supported is also porous, the fineness of the adsorption substrate, which was a disadvantage of the conventional method of kneading the adsorption substrate and the binder, The adsorption site is rarely clogged with a binder, and the adsorption substrate can be used effectively. Here, the fibril means a fibrous structure formed of an organic polymer resin and forming a three-dimensional continuous network structure on the outer surface and inside of the molded body.

  The void inside the fibril and the opening of the fibril surface are determined by observing the cut section of the molded body with a scanning electron microscope. It is observed that there are voids in the cross-section of the fibril and that the surface of the fibril is open. Further, it is observed that the inorganic ion adsorbent powder is supported on the outer surface of the fibril and the inner void surface. The thickness of the fibril is preferably O.01 μm to 50 μm. The pore diameter on the fibril surface is preferably O.001 μm to 5 μm.

  In the porous molded body of the present invention, the communicating holes preferably have a maximum pore diameter layer in the vicinity of the surface of the molded body. Here, the maximum pore diameter layer means the largest portion in the pore diameter distribution of the communication holes extending from the surface of the molded body to the inside. When there is a large circular or oval (finger-shaped) void called a void, the layer in which the void exists is called the maximum pore diameter layer. The vicinity of the surface means the inner side up to 25% of the cleaved diameter of the molded body from the outer surface toward the center. By having the maximum pore diameter layer in the vicinity of the surface of the molded body, it has the effect of accelerating the diffusion of the substance to be adsorbed into the interior. Therefore, the adsorption target substance such as phosphorus can be quickly taken into the molded body and removed from the treated water.

  The positions of the maximum pore diameter and the maximum pore diameter layer are determined by observing the surface and the cut surface of the molded body with a scanning electron microscope. As the hole diameter, when the hole is circular, the diameter thereof is used. When the hole is not circular, the equivalent circle diameter of a circle having the same area is used. The form of the molded body can take any form such as a particulate form, a thread form, a sheet form, a hollow fiber form, a cylindrical form, and a hollow cylindrical form. In particular, when the molded body is used as an adsorbent in the water treatment field, the particle shape is reduced in terms of pressure loss, effectiveness of the contact area and ease of handling when packed in a column or the like and passed through. Spherical particles (not only true spheres but also oval spheres) are particularly preferable.

  The average particle diameter of the spherical molded body of the present invention is a mode diameter (most frequent particle diameter) of a sphere equivalent diameter obtained from the angular distribution of scattered light intensity of diffraction by laser light, assuming that the particles are spherical. A preferable range of the average particle diameter is 100 to 2500 μm, particularly 200 to 2000 μm. If the average particle size is smaller than 100 μm, the pressure loss tends to increase when the column or tank is filled, and if the average particle size is larger than 2500 μm, the surface area when packed in the column or tank is reduced. Processing efficiency tends to decrease.

The porosity Pr (%) of the molded body of the present invention is the weight W1 (g) of the molded body when it contains water, the weight W0 (g) after drying, and the specific gravity of the molded body as ρ. The value represented by
Pr = (W1-WO) / (W1-WO + W0 / ρ) × 100
The wet weight may be determined by spreading a molded product sufficiently wet with water on dry filter paper and taking excess water before measuring the wet weight. Drying may be performed under vacuum at room temperature in order to eliminate moisture. The specific gravity of the molded body can be easily measured using a specific gravity bottle.
A preferable range of the porosity Pr (%) is 50% to 90%, and particularly preferably 60 to 85%. If it is less than 50%, the contact frequency between the adsorption target substance such as phosphorus and the inorganic ion adsorbent as the adsorption substrate tends to be insufficient. If it exceeds 90%, the strength of the molded product tends to be insufficient.

The supported amount of the inorganic ion adsorbent in the molded product of the present invention is a value represented by the following formula when the weight Wd (g) when the molded product is dried and the weight Wa (g) of the ash content.
Load (%) = Wa / Wd × 100
Here, the ash content is the residue when the molded product of the present invention is baked at 800 ° C. for 2 hours.
A preferable loading range is 30 to 95%, more preferably 40 to 90%, and particularly preferably 65 to 90%. If it is less than 30%, the contact frequency between the adsorption target substance such as phosphorus and the inorganic ion adsorbent as the adsorption substrate tends to be insufficient, and if it exceeds 95%, the strength of the molded product tends to be insufficient.
According to the method of the present invention, unlike the conventional attaching method, since the adsorbing substrate and the organic polymer resin are kneaded and molded, it is possible to obtain a molded body having a large carrying amount and strong strength.

The specific surface area of the molded product of the present invention is defined by the following formula.
Specific surface area (m ² / cm ³ ) = S _BET × Bulk specific gravity (g / cm ³ )
Here, S _BET is a specific surface area (m ² / g) per unit weight of the molded body.
The specific surface area is measured using the BET method after vacuum drying the molded body at room temperature.
The bulk specific gravity is measured by measuring the apparent volume of a short shaped product such as a particle, a column, or a hollow column using a wet compact and a graduated cylinder. Then, it vacuum-drys at room temperature and calculates | requires a weight.

For a long fiber-like, hollow fiber-like, or sheet-like shape, the cross-sectional area and length when wet are measured, and the volume is calculated from the product of both. Then, it vacuum-drys at room temperature and calculates | requires a weight.
The preferred range of the specific surface area is ^{5m 2 / cm 3 ~500m 2 /} cm 3. If it is less than 5 m ² / cm ³ , the amount of the adsorbed substrate and the adsorption performance tend to be insufficient, and if it exceeds 500 m ² / cm ³ , the strength of the molded product tends to be insufficient.
In general, the adsorption performance (adsorption capacity) of an inorganic ion adsorbent that is an adsorption substrate is often proportional to the specific surface area. If the surface area per unit volume is small, the adsorption capacity and adsorption performance when packed in a column or tank are small, making it difficult to achieve high-speed processing.

  The molded body of the present invention has a three-dimensional network structure that is porous and intricately intertwined with fibrils. Furthermore, since the fibril itself has voids, it has a feature that the surface area is large. Since this has an adsorption substrate (inorganic ion adsorbent) having a larger specific surface area, the surface area per unit volume is also increased.

Next, the manufacturing method of the porous molded object of this invention is demonstrated.
The method for producing a porous molded body of the present invention is characterized in that an organic polymer resin, a good solvent thereof, an inorganic ion adsorbent, and a water-soluble polymer are mixed and then molded and solidified in a poor solvent. .
The organic polymer resin used in the present invention is not particularly limited, but is preferably one that can be made porous by wet phase separation. For example, polysulfone polymer, polyvinylidene fluoride polymer, polyvinylidene chloride polymer, acrylonitrile polymer, polymethyl methacrylate polymer, polyamide polymer, polyimide polymer, cellulose polymer, ethylene vinyl alcohol copolymer polymer, etc. There are many types. In particular, ethylene vinyl alcohol copolymer (EVOH), polyacrylonitrile (PAN), polysulfone (PS), and polyvinylidene fluoride (PVDF) are preferable from the viewpoint of non-swelling property and biodegradability in water and ease of production. Furthermore, an ethylene vinyl alcohol copolymer (EVOH) is preferable because it has both hydrophilicity and chemical resistance.

  In addition, the good solvent used in the present invention may be any as long as it dissolves both the organic polymer resin and the water-soluble polymer. For example, dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF) and the like. These good solvents may be used alone or as a mixed solvent. The content of the organic polymer resin in the good solvent is not particularly limited, but is preferably 5 to 40% by weight, and more preferably 7 to 30% by weight. If it is less than 5% by weight, it is difficult to obtain a strong molded product. When it exceeds 40% by weight, it is difficult to obtain a porous molded body having a high porosity.

  The water-soluble polymer used in the present invention is not particularly limited as long as it is compatible with the organic polymer resin. Examples of natural polymers include guar gum, locust bean gum, carrageenan, gum arabic, tragacanth, pectin, starch, dextrin, gelatin, casein, collagen and the like. Examples of the semisynthetic polymer include methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl starch, and methyl starch. Furthermore, examples of the synthetic polymer include polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl methyl ether, carboxyvinyl polymer, sodium polyacrylate, and polyethylene glycols such as tetraethylene glycol and triethylene glycol. Among these water-soluble polymers, a synthetic polymer is preferable in that it has biodegradability resistance.

  In particular, it is particularly preferable to use polyvinylpyrrolidone as the water-soluble polymer because it has a high effect of developing a structure having voids inside the fibrils forming the communication holes as in the molded article of the present invention. The weight average molecular weight of polyvinylpyrrolidone is preferably in the range of 2,000 to 2,000,000, more preferably in the range of 2,000 to 1,000,000, and still more preferably in the range of 2,000 to 100,000. If the weight average molecular weight is less than 2,000, the effect of developing a structure having voids inside the fibril tends to be low. If the weight average molecular weight exceeds 2,000,000, the viscosity at the time of molding increases, and molding is difficult. It tends to be difficult.

The content of the water-soluble polymer in the molded product of the present invention is expressed by the following equation when the weight of the molded product when dried is Wd (g) and the weight of the water-soluble polymer extracted from the molded product is Ws (g). The value represented.
Content (%) = Ws / Wd × 100
The content of the water-soluble polymer depends on the type and molecular weight of the water-soluble polymer, but is preferably 0.001 to 10%, and more preferably 0.01 to 1%. If it is less than 0.001%, the effect is not necessarily sufficient to open the surface of the molded body, and if it exceeds 10%, the polymer concentration becomes relatively thin and the strength may not be sufficient.

  Here, the weight Ws of the water-soluble polymer in the molded body is measured as follows. First, after the dried molded body is pulverized in a mortar or the like, the water-soluble polymer is extracted from the pulverized product using a good solvent for the water-soluble polymer, and then the extract is evaporated to dryness, The weight of the conducting polymer is determined. Furthermore, identification of the extracted evaporated and dried product and confirmation of the presence or absence of the water-soluble polymer remaining in the fibril and not extracted can be measured by infrared absorption spectrum (IR) or the like.

  Furthermore, when there is a water-soluble polymer that remains in the fibrils and is not extracted, the porous molded body of the present invention is dissolved in a good solvent for both the organic polymer resin and the water-soluble polymer, and then the inorganic ions are dissolved. A liquid obtained by removing the adsorbent by filtration can be prepared, and then the liquid can be analyzed using GPC or the like to quantify the content of the water-soluble polymer.

  The content of the water-soluble polymer can be appropriately adjusted depending on the molecular weight of the water-soluble polymer and the combination of the organic polymer resin and the good solvent. For example, when a water-soluble polymer having a high molecular weight is used, the entanglement of the molecular chain with the organic polymer resin becomes strong, and it becomes difficult to move to the poor solvent side during molding, and the content can be increased.

The inorganic ion adsorbent used in the present invention refers to an inorganic substance exhibiting an ion adsorption phenomenon.
For example, natural products include zeolite, montmorillonite, and various mineral substances, and synthetic products include metal oxides. The former is represented by aluminosilicate kaolin mineral with a single layer lattice, bilayer latticed muscovite, sea chlorite, kanuma earth, pyrophyllite, talc, three-dimensional framework feldspar, zeolite and the like. The latter mainly includes polyvalent metal salts, metal oxides, insoluble heteropolyacid salts, insoluble hexacyanoferrates, and the like.

Examples of the polyvalent metal salt include hydrotalcite compounds represented by the following formula (II).
M ²⁺ _(1-X) M ³⁺ _x (OH ⁻ ) _{(2 + xy)} (A ⁿ⁻ ) y / n (II)
[ ^Wherein M ²⁺ represents at least one divalent metal ion selected from the group consisting of Mg ²⁺ , Ni ²⁺ , Zn ²⁺ , Fe ²⁺ , Ca ²⁺ and Cu ²⁺ ; ³⁺ represents at least one trivalent metal ion selected from the group consisting of Al ³⁺ and Fe ^3+, a ^n-represents an n-valent anion, be 0.1 ≦ x ≦ 0.5 0.1 ≦ y ≦ 0.5, and n is 1 or 2. ]
The metal oxide can be represented by the following formula (I).
_{MN x O n · mH 2 O} (I)
(Wherein x is 0 to 3, n is 1 to 4, m is 0 to 6, and M and N are Ti, Zr, Sn, Sc, Y, La, Ce, Pr, Nd, Sm, Eu. Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Si, Cr, Co, Ga, Fe, Mn, Ni, V, Ge, Nb and Ta are metal elements selected from the group Are different from each other.)

The metal oxide referred to in the present invention may be an unhydrated (non-hydrated) metal oxide in which m in the formula (I) can be represented by 0, or a hydrate (m can be represented by a numerical value other than 0). It may be a hydrous metal oxide.
The metal oxide in the case where x in formula (I) is a numerical value other than 0 is such that each contained metal element has regularity and is uniformly distributed throughout the oxide, for example, a perovskite structure, spinel It forms a structure and the like, and is contained in metal oxides such as nickel ferrite (NiFe ₂ O ₄ ) and zirconium hydrous ferrite (Zr · Fe ₂ O ₄ · mH ₂ O m is 0.5 to 6). It is a complex metal oxide represented by a chemical formula in which the composition ratio of each metal element is fixed.

The inorganic ion adsorbent supported on the porous molded body of the present invention is represented by the above formula (I) and has the following (a) to (a) to (a) to (a) to (a) to (a) It is preferable that it is a 1 type, or 2 or more types of mixture of the metal oxide chosen from the group in any one of c).
(A) hydrated titanium oxide, hydrated zirconium oxide, hydrated tin oxide, hydrated cerium oxide, hydrated lanthanum oxide, and hydrated yttrium oxide (b) consisting of titanium, zirconium, tin, cerium, lanthanum, and yttrium A composite metal oxide of a metal element selected from the group and a metal element selected from the group consisting of aluminum, silicon, and iron (c) activated alumina In addition, activated alumina loaded with aluminum sulfate, activated carbon loaded with aluminum sulfate, and the like are also preferred.

The metal oxide represented by the formula (I) used in the present invention may be a solid solution of metal elements other than M and N. For example, the hydrated zirconium oxide represented by the formula ZrO ₂ · mH ₂ O according to the formula (I) may be hydrated zirconium oxide in which iron is dissolved.
The inorganic ion adsorbent used in the present invention may contain a plurality of metal oxides represented by the formula (I). There are no particular restrictions on the distribution state of each metal oxide, but in order to obtain an inorganic ion adsorbent that has better cost performance by effectively utilizing the characteristics of each metal oxide, the surroundings of a specific metal oxide Is preferably a mixed structure covered with another metal oxide. An example of such a structure is a structure in which hydrated zirconium oxide covers the periphery of triiron tetroxide.

  In addition, since the metal oxide referred to in the present invention includes a metal oxide in which other elements are dissolved, the hydrated zirconium oxide in which iron is dissolved in the surrounding area of triiron tetroxide in which zirconium is in solid solution. The covered structure can also be illustrated as a preferred example.

In the above example, hydrated zirconium oxide has high adsorption performance for ions such as phosphorus, boron, fluorine, arsenic and durability for repeated use, but is expensive. On the other hand, triiron tetroxide has a low adsorption performance for ions such as phosphorus, boron, fluorine, and arsenic and a durability performance for repeated use, but is very inexpensive.
Therefore, when the structure of iron tetroxide is covered with hydrated zirconium oxide, the surface of the inorganic ion adsorbent that is involved in the adsorption of ions becomes hydrated zirconium oxide with high adsorption performance and durability. Since the inside which does not participate in adsorption becomes inexpensive iron trioxide, a porous molded body which can be used as an adsorbent having high adsorption performance, high durability performance and low cost, that is, excellent in cost performance is obtained.

In addition, for adsorption and removal of ions harmful to the environment and health of phosphorus, boron, fluorine, arsenic,
From the viewpoint of obtaining an adsorbent excellent in cost performance, the inorganic ion adsorbent used in the present invention is a metal element in which at least one of M and N in the formula (I) is selected from the group consisting of aluminum, silicon, and iron. A structure in which at least one of M and N in the formula (I) is covered with a metal oxide that is a metal element selected from the group consisting of titanium, zirconium, tin, cerium, lanthanum, and yttrium. It is preferable to be configured.

  In this case, the content ratio of the metal element selected from the group consisting of aluminum, silicon, and iron in the inorganic ion adsorbent is a metal element selected from the group consisting of aluminum, silicon, and iron, and titanium, zirconium, tin, cerium, The total number of moles of the metal element selected from the group consisting of lanthanum and yttrium is T, the number of moles of the metal element selected from the group consisting of aluminum, silicon, and iron is F, and F / T (molar ratio) is 0.00. The range is preferably from 01 to 0.95, more preferably from 0.1 to 0.90, still more preferably from 0.2 to 0.85, and from 0.3 to 0.80. It is particularly preferred that When the value of F / T (molar ratio) is excessively increased, the adsorption performance and durability performance tend to be lowered.

Also, depending on the metal, there are a plurality of forms of metal oxides with different oxidation numbers of the metal elements, but the form is not limited as long as it can exist stably in the inorganic ion adsorbent. For example, in the case of an iron oxide, hydrated ferric oxide (FeO _1.5 · mH ₂ O) or hydrated iron trioxide (FeO _1.33 · mH ₂ O) is preferred.
In addition, the inorganic ion adsorbent of the present invention may contain an impurity element mixed due to its production method or the like within a range not departing from the achievement of the object of the present invention. Possible impurity elements to be mixed include nitrogen (nitrate, nitrite, ammonium), sodium, magnesium, sulfur, chlorine, potassium, calcium, copper, zinc, bromine, barium, hafnium, and the like.

In addition, since the specific surface area of the inorganic ion adsorbent affects the adsorption performance and durability, the specific surface area is preferably within a certain range. Specifically, it is preferable that a BET specific surface area determined by nitrogen adsorption method is 20~1000m ² / g, more preferably 30~800m ² / g, it is 50 to 600 m ² / g More preferably, it is 60-500 m < ² > / g. If the BET specific surface area is too small, the adsorption performance decreases, and if it is too large, the solubility in acids and alkalis increases, and as a result, the durability performance against repeated use decreases.
Although the manufacturing method of the metal oxide represented by the formula (I) used in the present invention is not particularly limited, for example, it is manufactured by the following method. A precipitate obtained by adding an alkaline solution to an aqueous salt solution of the metal chloride, sulfate, nitrate or the like is filtered, washed, and dried. The drying is performed by air drying or at about 150 ° C. or less, preferably about 90 ° C. or less for about 1 to 20 hours.

  Next, around at least one of M and N in the formula (I) around the metal oxide in which at least one of M and N in the formula (I) is a metal element selected from the group consisting of aluminum, silicon and iron A method for producing an inorganic ion adsorbent comprising a metal oxide that is a metal element selected from the group consisting of titanium, zirconium, tin, cerium, lanthanum, and yttrium. An example of manufacturing an inorganic ion adsorbent having a structure covered with zirconium oxide will be described.

  First, salts obtained by mixing a salt such as zirconium chloride, nitrate or sulfate with a salt such as iron chloride, nitrate or sulfate so that the above-mentioned F / T (molar ratio) is a desired value. Make an aqueous solution. Thereafter, an aqueous alkaline solution is added to adjust the pH to 8 to 9.5, preferably 8.5 to 9 to form a precipitate. Thereafter, the temperature of the aqueous solution is set to 50 ° C., air is blown in while maintaining the pH at 8 to 9.5, preferably 8.5 to 9, and oxidation is performed until ferrous ions cannot be detected in the liquid phase. The resulting precipitate is filtered off, washed with water and dried. The drying is performed by air drying or at about 150 ° C. or less, preferably about 90 ° C. or less for about 1 to 20 hours. The moisture content after drying is preferably in the range of about 6 to 30% by weight.

Zirconium oxychloride (ZrOC1 ₂ ), zirconium tetrachloride (ZrC1 ₄ ), zirconium nitrate (Zr (NO ₃ ) ₄ ), zirconium sulfate (Zr (SO ₄ ) ₂ ) Etc. These may be hydrated salts such as Zr (SO ₄ ) ₂ .4H ₂ O. These metal salts are usually used in the form of a solution of about 0.05 to 2.O moles per liter.
Examples of the iron salt used in the above-described production method include ferrous salts such as ferrous sulfate (FeSO ₄ ), ferrous nitrate (Fe (NO ₃ ) ₂ ), and ferrous chloride (FeC1 ₂ ). Can be mentioned. These may also be hydrated salts such as FeSO ₄ .7H ₂ O.

  These ferrous salts are usually added as solids, but may be added in the form of a solution. Examples of the alkali include sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia, sodium carbonate and the like. These are preferably used in an aqueous solution of about 5-20% by weight. When the oxidizing gas is blown, the time varies depending on the kind of the oxidizing gas, but is usually about 1 to 10 hours. As the oxidizing agent, for example, hydrogen peroxide, sodium hypochlorite, potassium hypochlorite and the like are used.

The inorganic ion adsorbent of the present invention is preferably as fine as possible, and its particle size is in the range of 0.01 to 100 μm, preferably 0.01 to 50 μm, more preferably 0.01 to 30 μm. .
If the particle size is smaller than 0.01 μm, the viscosity of the slurry at the time of production tends to increase and it tends to be difficult to mold. If it exceeds 100 μm, the specific surface area tends to be small, and the adsorption performance tends to be lowered.
The particle diameter here refers to the particle diameter of both the primary particles and the secondary particles in which the primary particles are aggregated or a mixture. The particle diameter of the inorganic ion adsorbent of the present invention is a sphere equivalent diameter (most frequent particle diameter) obtained from the angular distribution of scattered light intensity of diffraction by laser light.

  As the poor solvent of the method of the present invention, for example, water, alcohols such as methanol, ethanol, organic polymer resins such as industrial hydrocarbons, aliphatic hydrocarbons such as n-hexane and n-heptane are dissolved. Liquid is used, but water is preferred. It is also possible to control the coagulation rate by adding a little good solvent of the organic polymer resin in the poor solvent. The mixing ratio of the good solvent of the polymer resin and water is preferably O to 40%, and more preferably 0 to 30%. When the mixing ratio exceeds 40%, the coagulation rate becomes slow, so the polymer solution formed into droplets etc. enters between the poor solvent and the molded body between the poor solvent and the molded body. The shape tends to be distorted by the influence of friction resistance.

  The temperature of the poor solvent is not particularly limited, but is preferably −30 ° C. to 90 ° C., more preferably O ° C. to 90 ° C., and further preferably 0 ° C. to 80 ° C. If the temperature of the poor solvent exceeds 90 ° C or is less than -30 ° C, the state of the molded body in the poor solvent is difficult to stabilize.

Next, an ion processing method using the porous molded body of the present invention as an adsorbent will be described.
The porous molded body of the present invention is suitable for use as an adsorbent for adsorbing and removing ions in water by contacting with a liquid.
The ions to be adsorbed by the porous molded body of the present invention are not particularly limited to anions and cations. For example, with anions, phosphorus (phosphate ions), fluorine (fluoride ions), arsenic (arsenate ions, arsenite ions), boron (borate ions), iodine ions, chlorine ions, sulfate ions, nitrate ions , Nitrite ions, and ions of various organic acids such as acetic acid. Examples of the cation include sodium, potassium, calcium, cadmium, lead, chromium, cobalt, strontium, and cesium.

In particular, inorganic ion adsorbents have the characteristic of specific selectivity for certain ions, so that ions such as phosphorus are removed from the presence of miscellaneous ions such as sewage and industrial wastewater. Suitable for doing.
Specifically, for removal of phosphorus, boron, fluorine and arsenic ions, hydrated titanium oxide, hydrated zirconium oxide, hydrated tin oxide, hydrated cerium oxide, hydrated lanthanum oxide, hydrate Yttrium oxide; a composite metal oxide of a metal element selected from the group consisting of titanium, zirconium, tin, cerium, lanthanum, and yttrium and a metal element selected from the group consisting of aluminum, silicon, and iron; activated alumina; It is preferable to select at least one metal oxide selected from the group consisting of activated alumina; and aluminum sulfate impregnated activated carbon.

  When the porous molded body of the present invention is used as an adsorbent in water treatment applications, the porous molded body is usually used by being filled in a container, but the shape of the container and the shape of the packed layer of the porous molded body There is no particular limitation as long as the porous molded body can be brought into contact with water to be treated, and examples thereof include cylindrical, columnar, polygonal columnar, and box-shaped containers. Preferably, packing in a column or adsorption tower and allowing the water to be treated to flow through and contact with each other can sufficiently bring out the high contact efficiency that is characteristic of the porous molded body.

These containers are preferably provided with a solid-liquid separation mechanism that prevents the porous molded body from flowing out of the container, for example, a pan and a mesh.
The material of the container is not particularly limited, and examples include stainless steel, FRP (reinforced plastic with glass fiber), glass, and various plastics. In consideration of acid resistance, the inner surface may be made of rubber or fluororesin lining.

  The contact method between the porous molded body and the water to be treated is not particularly limited as long as the porous molded body and the water to be treated can be brought into contact with each other. When the porous molded body is used as a fixed bed, a method of passing water in an upward or downward flow through a cylindrical, polygonal, or box-shaped porous molded body, or cylindrical porous molding Examples include an external pressure system that allows water to flow from the outer circumferential side to the inner cylinder, an internal pressure system that allows water to flow in the opposite direction, and a system that allows water to flow horizontally to the box-shaped packed bed. The packed bed of the porous molded body may be a fluidized bed system.

  The ion adsorbing means of the present invention is not particularly limited, but can adopt a merry-go-round system. With the merry-go-round method, a plurality of ion adsorbing means are arranged in series to conduct water, and when the adsorption capacity of the ion adsorbing means in the previous stage is reduced, the water passing through the ion adsorbing means is stopped and located in the subsequent stage This is a method of obtaining treated water with a stable water quality by sequentially passing water through the ion adsorbing means with a time difference from the previous stage, such as passing the ion adsorbing means as the front stage.

  In the ion adsorption means and the ion processing method of the present invention, the desorption operation and the activation operation described later are generally performed at the same site where the adsorption operation is performed. However, if there is not enough space at the site or the frequency of desorption is low, only the column can be removed from the apparatus and replaced with a new column separately. The removed column can be separately processed and reused in a factory equipped with a desorption and activation facility.

  When the porous molded body of the present invention is used as an adsorbent in water treatment applications, it is preferable to provide means for solid-liquid separation of suspended substances in water as a pretreatment. By removing suspended substances in water in advance, the surface of the porous molded body can be prevented from being blocked, and the adsorption performance of the porous molded body of the present invention can be sufficiently exhibited. Preferable solid-liquid separation means includes coagulation sedimentation, sedimentation separation, sand filtration, and membrane separation. In particular, a membrane separation technique that has a small installation area and that provides clear filtrate water is preferable. Preferred membrane separation techniques include reverse osmosis membrane (RO), ultrafiltration membrane (UF), microfiltration membrane (MF) and the like. The form of the membrane is not limited to flat membranes, hollow fibers, pleats, spirals, tubes and the like.

In the adsorption step of the present invention, it is preferable to adsorb the ions to be adsorbed after adjusting the pH of the liquid to a suitable pH by a combination of ions to be adsorbed and the inorganic ion adsorbent.
For example, the pH adjustment range when using an inorganic ion adsorbent having a structure in which phosphorus in a liquid is to be adsorbed and hydrated zirconium oxide or iron tetroxide is covered with hydrated zirconium oxide is pH 1.5 to 10. It is a range, More preferably, it is pH 2-7.
In addition, the pH adjustment range when using an inorganic ion adsorbent with a structure in which boron in the liquid is to be adsorbed and hydrated cerium oxide or iron tetroxide is covered with hydrated cerium oxide is in the range of pH 3 to 10. Yes, more preferably pH 5-8.

In addition, the pH adjustment range when using an inorganic ion adsorbent with a structure in which fluorine in the liquid is to be adsorbed and hydrated cerium oxide or iron trioxide is covered with hydrated zirconium oxide is in the range of pH 1-7. Yes, more preferably pH 2-5.
Also, the pH adjustment range when using an inorganic ion adsorbent with a structure in which arsenic in the liquid is the target of adsorption and hydrated cerium oxide or iron tetroxide is covered with hydrated cerium oxide is in the range of pH 3-12. Yes, more preferably pH 5-9.

  The porous molded body of the present invention can adsorb the anions again by contacting the alkaline aqueous solution to desorb the adsorbed anions and then treating the adsorbent with an acidic aqueous solution (re-applying). Use). By reusing the porous molded body, not only the cost can be reduced, but also the waste can be reduced. In particular, since the porous molded body of the present invention is excellent in durability, it is suitable for repeated use.

An anion can be eliminated when the pH of the alkaline solution is at least pH 10, but is preferably at least pH 12, more preferably at least pH 13. The alkali concentration is in the range of O.1 wt% to 30 wt%, more preferably in the range of 0.5 to 20 wt%. If it is thinner than O.1 wt%, the desorption efficiency is low, and if it is thicker than 30 wt%, the cost of alkali chemicals tends to increase.
The flow rate of the alkaline aqueous solution is not particularly limited, but is usually preferably in the range of SV0.5 to 15 (hr ⁻¹ ). When it is lower than SVO.5, the desorption time tends to be long and tends to be inefficient, and when it is larger than SV15, the contact time between the porous molded body and the alkaline aqueous solution is shortened, and the desorption efficiency tends to decrease. The kind of the alkaline aqueous solution is not particularly limited, but usually an inorganic alkali such as sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonium hydroxide, and organic amines are used. Of these, sodium hydroxide and potassium hydroxide are particularly preferred because of their high desorption efficiency.

In the present invention, the desorbing alkali recycling step and the desorbing ion recovery step are performed by bringing an alkaline aqueous solution into contact with the porous molded body of the present invention that has adsorbed ions, eluting the ions in the alkaline solution, By adding a crystallization agent that generates ions and a precipitate and removing the precipitate, the alkali can be reused, and the ions can be recovered as a precipitate.
Examples of the crystallization agent include metal hydroxides. In the metal hydroxide, a metal salt combines with anions such as phosphorus, boron, fluorine, and arsenic to form a precipitate. Further, since the hydroxide becomes an alkali source of the desorption liquid, a closed system can be obtained by collecting and recycling the regenerated liquid. Specific examples include sodium hydroxide, aluminum hydroxide, magnesium hydroxide, and calcium hydroxide.

From the viewpoint of obtaining a hardly soluble precipitate, that is, a precipitate having low solubility, a polyvalent metal hydroxide is preferable, and specifically, aluminum hydroxide, magnesium hydroxide, and calcium hydroxide are particularly preferable. In particular, calcium hydroxide is preferable in terms of cost.
For example, when it exists as sodium phosphate, the alkali can be recovered according to the following reaction formula. Furthermore, the crystallized calcium phosphate can be recycled into fertilizers and the like.
6Na ₃ PO ₄ + 10Ca (OH) ₂ → 18NaOH + Ca10 (OH) ₂ (PO ₄ ) ₆ ↓
The addition amount of the metal hydroxide is not particularly limited, but is 1 to 4 times equivalent to the target ion. When the addition amount is equal to or less than the equimolar amount, the precipitation removal efficiency is low, and when it exceeds 4 times the equivalent, the removal efficiency hardly changes and tends to be economically disadvantageous.

When removing the precipitate, the pH is preferably 6 or more. Further, considering that the aqueous alkaline solution is recovered and reused, it is preferably maintained at pH 12 or more, preferably pH 13 or more. If the pH during the precipitation process is lower than 6, the solubility of the precipitate increases and the precipitation efficiency decreases. When removing the precipitate, an inorganic flocculant such as aluminum sulfate or polyaluminum chloride or a polymer flocculant can be used in combination with the metal hydroxide.
Further, the preferred desorbed ion recovery step in the present invention is to cool the desorbed liquid from which ions have been desorbed and to crystallize and remove the precipitate, thereby making it possible to reuse the alkali, Is to collect as.

This recovery process of desorbed ions by cooling can be suitably applied particularly when a porous molded body that has adsorbed phosphate ions is desorbed using sodium hydroxide.
The cooling means and method are not particularly limited, but can be cooled using a normal chiller, heat exchanger or the like.
The cooling temperature is not particularly limited as long as it is a temperature at which desorbed ions can be crystallized, but is preferably in the range of 5 to 25 ° C, more preferably in the range of 5 to 10 ° C. If the temperature is less than 5 ° C, a large amount of cooling energy is required, which tends to be economically disadvantageous. If the temperature is higher than 10 ° C, the effect of crystallizing the precipitate tends to be low.
In order to effectively crystallize sodium phosphate by cooling, sodium hydroxide can be newly added to increase the concentration of sodium hydroxide in the desorption liquid.
The method for solid-liquid separation of the precipitate in the desorption solution of the present invention is not particularly limited, but usually, sedimentation separation, centrifugal separation, belt press machine, screw press machine, membrane separation method and the like can be used.

In particular, the membrane separation method is preferable in that the installation area is small and clear filtered water can be obtained.
The membrane separation method is not particularly limited, and examples thereof include an ultrafiltration membrane (UF), a microfiltration membrane (MF), and a dialysis membrane. The form of the membrane is not limited to a flat membrane, a hollow fiber, a pleat, a tube shape or the like. As a preferable membrane separation method, an ultrafiltration membrane (UF), a microfiltration membrane (MF) and the like are preferable in terms of filtration speed and filtration accuracy.
The porous molded body in the column after the desorption step is alkaline, and as it is, the ability to adsorb ions in the raw water again is low. Therefore, an operation of returning the pH in the column to a predetermined value using an acidic aqueous solution, that is, an activation treatment is performed.

The acidic aqueous solution is not particularly limited, but an aqueous solution such as sulfuric acid and hydrochloric acid is used. The concentration may be about O.001 to 10 wt%. If it is thinner than O.001 wt%, a large amount of water volume is required by the end of activation, and if it is thicker than 10 wt%, there is a possibility that a problem may occur in terms of danger in handling an acidic aqueous solution.
The liquid passing speed is not particularly limited, but is usually preferably in the range of SV 0.5 to 30 (hr ⁻¹ ). If it is lower than SV0.5, the activation time tends to be long and inefficient, and if it is larger than SV30, the contact time between the porous molded body and the acidic aqueous solution becomes short, and the activation efficiency tends to decrease. is there.
A more preferable method in the activation method is to circulate the active solution between the column and the pH adjusting tank.

By adopting this configuration, the pH of the porous molded body in the column shifted to the alkali side by the desorption operation can be slowly returned to a predetermined pH in consideration of the acid resistance of the inorganic ion adsorbent.
For example, it is known that iron oxide is remarkably dissolved by acid at pH 3 or lower. When such iron oxide is supported on a porous molded body, the conventional activation method has a problem of dissolution of iron, and therefore, there is only a method of treating with a thin acid having a pH of 3 or more. However, this method requires a large volume of water and is not economically acceptable.
In contrast to such conventional techniques, the activation method of the present invention is provided with a column and a pH adjusting tank and circulates the activation liquid. Therefore, the activation method can be activated while avoiding the pH range in which it is dissolved by an acid. The volume of water used for conversion can be reduced, and the apparatus can be made compact.

The liquid passing speed at this time is usually selected in the range of SV1 to 200 (hr ⁻¹ ). More preferably, it is in the range of SV1O-100. If it is lower than SV1, the activation time tends to be long and tends to be inefficient, and if it is larger than SV200, a large pump movement is required and tends to be inefficient.
This series of desorption and activation operations can be performed while the column is filled with the adsorbent. That is, regeneration can be easily performed by passing an alkaline aqueous solution and an acidic aqueous solution sequentially through the column after the adsorption operation is completed in the column packed with the adsorbent. In this case, the liquid flow direction may be either an upward flow or a downward flow.
Since the porous molded article of the present invention is excellent in chemical resistance and strength, the ion adsorption performance is hardly lowered even if this regeneration treatment is repeated several tens to several hundreds of times.

The present invention will be described based on examples.
[Production Example 1] Production of inorganic ion adsorbent 1 liter of an O.15 molar aqueous solution of zirconium oxychloride (ZrOC1 ₂ ) was prepared. This solution contained 13.7 g of metal ions as zirconium. In this aqueous solution, 84.Og of ferrous sulfate crystals (FeSO ₄ · 7H ₂ O) was added and dissolved while stirring. This amount corresponds to 0.3 mol of iron ion (F / T (molar ratio) 0.67).

Next, a 15% by weight sodium hydroxide solution was added dropwise to this aqueous solution while stirring until the pH of the solution reached 9, resulting in a blue-green precipitate. Next, air was blown in at a flow rate of 10 liters / hour while the aqueous solution was heated to 50 ° C. When the air blowing was continued, the pH of the aqueous solution was lowered. In this case, a 15 wt% sodium hydroxide solution was dropped to maintain the pH at 8.5-9. When the blowing of air was continued until no ferrous ions could be detected in the liquid phase by spectrophotometric analysis, a black precipitate was formed.
The black precipitate was then filtered off with suction, washed with deionized water until the filtrate was neutral, and dried at 70 ° C. or lower. This was pulverized with a ball mill for 7 hours to obtain an inorganic ion adsorbent powder having an average particle size of 2.8 μm. The BET specific surface area of this powder was 170 m ² / g. The structure of the obtained inorganic ion adsorbent powder is based on the results of observation and analysis with a transmission electron microscope equipped with X-ray diffraction analysis and elemental analysis equipment. ) Was covered with hydrated zirconium oxide (possibly with solid solution of iron).

[Production Example 2] Production method of porous molded body Ethylene vinyl alcohol copolymer (EVOH, Nippon Synthetic Chemical Industry Co., Ltd., Soarnol E3803 (trade name)) 10 g, Polyvinylpyrrolidone (PVP, BASF Japan Co., Ltd., Luvitec) 10 g of K30 Powder (trade name) and 80 g of dimethyl sulfoxide (DMSO, Kanto Chemical Co., Inc.) were dissolved by heating at 60 ° C. in a Separa flask to obtain a uniform polymer solution. To 100 g of this polymer solution, 92 g of the inorganic ion adsorbent powder prepared in Production Example 1 was added and mixed well to obtain a slurry.

The obtained composite polymer slurry was heated to 40 ° C., and supplied to the inside of a cylindrical rotating container having a nozzle with a diameter of 5 mm on the side surface. The container was rotated, and droplets were discharged from the nozzle by centrifugal force (15G). Was discharged into a coagulation bath made of water at 60 ° C. to coagulate the composite polymer slurry. Further, washing and classification were performed to obtain a spherical molded body having an average particle size of 623 μm.
Furthermore, when the surface and fractured surface of the obtained porous molded body were observed using a scanning electron microscope (SEM), the presence of a skin layer was not observed. In addition, a maximum pore diameter layer (void layer) was observed near the surface, and voids inside the fibril and pores on the fibril surface were also confirmed. Furthermore, it was observed that the inorganic ion adsorbent powder was supported on the outer surface of the fibril and the void surface inside the fibril.

[Example 1] Water purification system and water purification method The water purification system used in this example is an aquatic plant planting method using river water as inflow water, and Production Example 2 for treating outflow water from the wet field. It is comprised from the column filled with the porous molded object manufactured by (4). The wet field uses vegetation as a vegetation, the design residence time is 4 hours, the water area load is 0.576 m 3 / m 2 / day, and more than 3 years have passed since the reeds have grown.
The average annual water quality in the wetland was 0.45 mg / l inflow water (TP) (total phosphorus concentration) and 0.44 mg / l in effluent water (TP). The column is filled with 10 L of a porous molded body, and the effluent can be treated at 100 L / hour. The TP of the treated water treated with the column when the TP of the effluent water was 0.51 mg / l was 0.1 mg / l or less. It can be seen that if the water purification system of the present invention is used, the phosphorus concentration in the treated water can be made extremely low.

  The water purification system and water purification method of the present invention can be suitably used in the field of purifying water areas such as rivers, lakes, inner bays, and inland seas.

Claims (7)

  A water purification system comprising a direct purification means and an ion adsorption means filled with a porous molded body, wherein the porous molded body comprises an organic polymer resin and an inorganic ion adsorbent and opens to the outer surface. A porous molded body having a communication hole, having a void inside the fibril forming the communication hole, and at least a part of the void is open at the surface of the fibril, and an outer surface of the fibril; A water purification system which is a porous molded body in which an inorganic ion adsorbent is supported on the surface of an internal void.   The water purification system according to claim 1, wherein the direct purification means is an aquatic plant planting method.   The water purification system according to claim 1 or 2, wherein the communication hole is a porous molded body having a maximum pore diameter layer near the surface of the molded body.   Porous molded body, wherein the organic polymer resin comprises one or more selected from the group consisting of ethylene vinyl alcohol copolymer (EVOH), polyacrylonitrile (PAN), polysulfone (PS), and polyvinylidene fluoride (PVDF). The water purification system according to any one of claims 1 to 3. The water purification system according to any one of claims 1 to 4, wherein the inorganic ion adsorbent contains at least one metal oxide represented by the following formula (I).
_{MN x O n · mH 2 O} (I)
(Wherein x is 0 to 3, n is 1 to 4, m is 0 to 6, and M and N are Ti, Zr, Sn, Sc, Y, La, Ce, Pr, Nd, Sm, Eu. Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Si, Cr, Co, Ga, Fe, Mn, Ni, V, Ge, Nb and Ta are metal elements selected from the group Are different from each other.) The metal oxide represented by the formula (I) is one or a mixture of two or more selected from any of the following groups (a) to (c): The water purification system described.
(A) hydrated titanium oxide, hydrated zirconium oxide, hydrated tin oxide, hydrated cerium oxide, hydrated lanthanum oxide, and hydrated yttrium oxide (b) consisting of titanium, zirconium, tin, cerium, lanthanum, and yttrium A composite metal oxide of a metal element selected from the group and a metal element selected from the group consisting of aluminum, silicon, and iron (c) activated alumina   A water purification method comprising a direct purification step and an ion adsorption step filled with a porous molded body, wherein the porous molded body comprises an organic polymer resin and an inorganic ion adsorbent and opens to the outer surface. A porous molded body having a communication hole, having a void inside the fibril forming the communication hole, and at least a part of the void is open at the surface of the fibril, and an outer surface of the fibril; A water purification method, which is a porous molded body in which an inorganic ion adsorbent is supported on the inner void surface.