JP2017018864A - Drainage processing method and drainage processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of nitrite ion upon reduction in concentration of nitrate ion in drainage.SOLUTION: Aqueous solution containing at least nitrate ion is brought into contact with nitrate ion conversion material 20 capable of reducing nitrate ion in the aqueous solution and nitrite ion conversion material 21 consisting of metal oxide capable of converting nitrite ion to nitrate ion in the aqueous solution. As the nitrite ion conversion material, zeolite may be preferably utilized. As the nitrate ion conversion material, photocatalyst capable of reducing nitrate ion by ultraviolet light irradiation may be preferably utilized.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wastewater treatment method and wastewater treatment apparatus for nitrogen-containing wastewater containing nitrate nitrogen.

In recent years, the outflow and accumulation of nitrogen into the environment has become a global problem, and there are concerns about adverse effects on animals and plants. Ammonia nitrogen (ammonium ion: NH ₄ ⁺ ), nitrate nitrogen (nitrate ion: NO ₃ ⁻ ), and nitrite nitrogen (nitrite ion: NO ₂ ⁻ ) contained in nitrogen-containing wastewater are treated by the Water Pollution Control Law. Emission standards are established. From the viewpoint of environmental protection, these nitrogen compounds have a possibility of stricter regulations, and a technique for reducing the concentration of nitrogen compounds is required. The means for removing nitrate nitrogen consisting of nitrate nitrogen and nitrite nitrogen include physicochemical methods (ion exchange, reverse osmosis, electrochemical dialysis, electroreduction, etc.), biological methods, and catalysts. The method used is known.

  For example, Patent Document 1 describes a wastewater treatment method in which nitrate ions are reduced by irradiating ultraviolet rays onto a photocatalyst in wastewater containing nitrate ions to reduce the nitrate ion concentration.

JP2013-116429A

  However, in the wastewater treatment method described in Patent Document 1, although the nitrate ion concentration is reduced, nitrite ions are by-produced.

  In the past, nitrite ions were released as nitrate nitrogen along with nitrate ions, but in recent years, as the danger of nitrite ions became clear, nitrite ions were added as a regulated substance for tap water. It was done. For this reason, it is required to reduce nitrite ions from waste water.

  In view of the above points, an object of the present invention is to suppress by-product formation of nitrite ions when the concentration of nitrate ions in waste water is reduced.

  In order to achieve the above object, in the invention of the wastewater treatment method according to claim 1, a nitrate ion conversion material (20) capable of reducing nitrate ions in an aqueous solution to an aqueous solution containing at least nitrate ions; It is characterized by contacting a nitrite ion conversion material (21) made of a metal oxide capable of converting nitrite ions in an aqueous solution into nitrate ions.

  According to the present invention, nitrate ions are reduced by a nitrate ion conversion material to reduce the nitrate ion concentration, and nitrite ions by-produced at that time are oxidized by the nitrite ion conversion material and converted to nitrate ions. it can. Thereby, when reducing the nitrate ion concentration of waste water, the by-product of nitrite ion can be suppressed and the nitrite ion concentration in waste water can be reduced.

  As a nitrite ion conversion material, zeolite can be preferably used. Moreover, as a nitrate ion conversion material, the photocatalyst which can reduce nitrate ion by ultraviolet irradiation can be used suitably.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

It is explanatory drawing which shows the structure of the waste water treatment equipment of embodiment to which this invention is applied. It is a graph which shows the nitrate ion concentration and nitrite ion concentration after performing a waste_water | drain process. It is explanatory drawing which shows the structure of the waste water treatment equipment of the modification of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In the wastewater treatment apparatus of this embodiment, a wastewater treatment unit 10 is provided. The wastewater treatment unit 10 is configured as a container that can accommodate wastewater therein. The waste water of the present embodiment is a nitrogen compound-containing waste water as long as it contains at least nitrate ions (NO ₃ ⁻ ) as nitrogen compounds, and further nitrite ions (NO ₂ ⁻ ) and ammonium ions (NH ₄ ⁻ ). Etc. may be included.

  Although not shown, the waste water treatment unit 10 is provided with an inflow port through which waste water flows and an outflow port through which waste water flows out. Wastewater is supplied to the wastewater treatment unit 10 from the outside through an inflow port. The wastewater that has flowed into the wastewater treatment unit 10 is discharged from the outlet after the concentration of nitrate ions is reduced inside the wastewater treatment unit 10. In the present embodiment, nitrite ions are suppressed as much as possible when the concentration of nitrate ions is reduced. The supply and discharge of the waste water can be performed using a pumping means such as a pump.

  A nitrate ion conversion material 20 for reducing nitrate ions and a nitrite ion conversion material 21 for oxidizing nitrite ions are arranged inside the waste water treatment unit 10.

In the present embodiment, as the nitrate ion conversion material 20, a photocatalyst that reduces nitrate ions in wastewater by ultraviolet irradiation is used. As the photocatalytic material, a layered perovskite compound BaLa ₄ Ti ₄ O ₁₅ , SrTiO ₃ , NaTaO ₃ or TiO ₂ is used, and among these, the layered perovskite compound BaLa ₄ Ti ₄ O ₁₅ is preferable.

The method for synthesizing the layered perovskite compound BaLa ₄ Ti ₄ O ₁₅ is not particularly limited, and a solid phase method or a complex polymerization method can be used, but a complex polymerization method is preferable in that a photocatalytic material having high activity can be obtained. . As a specific synthesis method by the complex polymerization method, a method described in JP2009-214033A can be used.

  The nitrate ion conversion material 20 of this embodiment has a structure in which a layered double hydroxide (LDH) represented by the following general formula (1) is partially modified on the surface of an ultraviolet light responsive oxide photocatalyst material. Have.

[M ²⁺ _1-x M ³⁺ (OH) ₂ ] [A ⁿ⁻ _{x / n} · yH ₂ O] (1)
Here, in the general formula (1), M ²⁺ was selected from Zn ²⁺ , Mn ²⁺ , Ni ²⁺ , Co ²⁺ , Fe ²⁺ , Cu ²⁺ , Ca ²⁺ and Mg ²⁺ . It is at least one kind of divalent metal ion (hereinafter referred to as “specific divalent metal ion”). These specific divalent metal ions can be used alone or in combination of two or more thereof. Among these specific divalent metal ions, Mg ²⁺ , Zn ²⁺ , Ni ²⁺ , Fe ²⁺ is preferred.

In the general formula (1), M ³⁺ represents at least one trivalent metal ion selected from Al ³⁺ , Cr ³⁺ , Fe ³⁺ , Co ³⁺ , Ce ³⁺ and Ga ³⁺ ( Hereinafter, it is referred to as “specific trivalent metal ion”. These specific trivalent metal ions can be used singly or in combination of two or more. Among these specific trivalent metal ions, Al ³⁺ and Fe ³⁺ are preferable.

As combinations of specific divalent metal ions and specific trivalent metal ions, a combination of Mg ²⁺ and Al ^{3+ and} a combination of Zn ²⁺ and Al ³⁺ have low toxicity and stability. It is preferable in that a specific layered double hydroxide is obtained that is high, has a low production cost, and has a low ultraviolet light absorbability.

In the general formula (1), A ⁿ⁻ is at least one anion selected from nitrate ion, carbonate ion and hydroxide, n is the valence of the anion, and these anions are each independently Or in combination.

  Further, in the general formula (1), x is a value of 0 or more and less than 1, preferably 0 to 0.44, more preferably 0 to 0.33. Since the anion adsorption ability of the layered double hydroxide is increased, high activity can be obtained. Y is a value of 0 or more.

  The ratio of the specific layered double hydroxide in the nitrate ion conversion material 20 is preferably 1 to 30% by mass, and more preferably 5 to 10% by mass. When this ratio is too small, the amount of active sites decreases, and the adsorption ability of nitrate ions also decreases. On the other hand, when this ratio is excessive, the surface of the photocatalyst is covered, so that the redox reaction by the photocatalyst hardly occurs and the activity is reduced.

  Further, in the nitrate ion conversion material 20, it is preferable that a Ni promoter is supported on the surface of the photocatalytic material. The supported amount of Ni promoter in the nitrate ion conversion material 20 is preferably 0.2 to 3% by mass, particularly 0.5 to 3% by mass. When the supported amount of Ni promoter is too small, sufficient reduction sites on the photocatalyst cannot be obtained. On the other hand, when the supported amount of Ni promoter is excessive, sintering occurs during firing, resulting in an increase in particle size and a decrease in dispersibility of the Ni promoter. In addition, light hitting the photocatalyst is shielded by the high concentration Ni promoter, and the photocatalytic activity is reduced.

  As a method for supporting the Ni promoter on the surface of the photocatalyst material, a nickel nitrate aqueous solution containing a predetermined amount of nickel is added to the photocatalyst material, followed by firing treatment, followed by heating in a hydrogen atmosphere for reduction treatment. The method can be used.

  The nitrite ion conversion material 21 is a catalyst that can oxidize nitrite ions and convert them into nitrate ions by contacting the nitrite ions. The following reaction occurs when the nitrite ions come into contact with the nitrite ion conversion material 21.

^{_{NO 2 - + 1 / 2O 2}} → NO 3 -
Nitrite ions are presumed to react with oxygen dissolved in water and be converted into nitrate ions.

The nitrite ion conversion material 21 is an oxide of one or more metals selected from molybdenum, tungsten, nickel, silicon, and aluminum. For example, MoO ₃ , WO ₃ , NiO, zeolite (SiO ₂ and Al ₂ O ₃ ). Can be used. Among these, in particular, molybdenum oxide (MoO ₃ ) or zeolite can be suitably used as the nitrite ion conversion material 21.

Zeolite is a general term for crystalline aluminosilicates, and the constituent elements are Al, Si, O and cations, which are based on a SiO ₄ and AlO ₄ tetrahedral structure. The cation contained in the zeolite is preferably a proton (H ⁺ ). Further, it is desirable that the ratio of silica (SiO ₂ ) / alumina (Al ₂ O ₃ ) in the zeolite is in the range of 10-100.

  As the zeolite, JRC-Z5-90H (1), HSZ-980HOA, HSZ-300 350HUA, HSZ-300 385HUA, JRC-Z-HM20 (5), JRC-Z-B25 (1), JRC-Z-HB25 (1) can be used. Among these types of zeolites, particularly when JRC-Z5-90H (1) is used, nitrite ions in the wastewater can be effectively converted into nitrate ions.

  The nitrate ion conversion material 20 and the nitrite ion conversion material 21 can be used in any shape, but in this embodiment, the granular nitrate ion conversion material 20 and the nitrite ion conversion material 21 are placed inside the wastewater treatment unit 10. Many are arranged. Thereby, the area which the nitrite ion contained in waste_water | drain contacts the nitrate ion conversion material 20 and the nitrite ion conversion material 21 can be enlarged.

  Further, the waste water treatment unit 10 is provided with a stirring unit 11 for stirring the waste water supplied from the outside, and an ultraviolet irradiation unit 12 for irradiating the waste water with ultraviolet rays. The stirring unit 11 can be rotated by a motor (not shown). By stirring the wastewater by the stirring unit 11, the contact frequency between the nitrite ion conversion material 21 and the wastewater can be increased. In this embodiment, a 100 W high-pressure mercury lamp is used as the ultraviolet irradiation unit 12.

  Next, the result of performing wastewater treatment using the wastewater treatment apparatus of this embodiment will be described. FIG. 2 shows the result of wastewater treatment using the nitrate ion conversion material 20 and the nitrite ion conversion material 21 of this embodiment and the result of wastewater treatment using only the nitrate ion conversion material 20 as a comparative example.

  In the example shown in FIG. 2, the nitrate ion conversion material 20 is 50 mg, the nitrite ion conversion material 21 is 10 mg, and 5 mL of waste water is used. Waste water having a nitrate ion concentration of 728.4 mg / L, a nitrite ion concentration below the detection limit, and an ammonium ion concentration of 13.5 mg / L was used.

As the nitrate ion conversion material 20 of the present embodiment and the comparative example, BaLa ₄ Ti ₄ O ₁₅ having a Ni promoter supported on the surface is used, a divalent metal ion constituting a layered double hydroxide and a specific trivalent ion The metal ions were Mg ²⁺ and Al ³⁺ . Moreover, the zeolite (JRC-Z5-90H (1)) was used as the nitrite ion conversion material 21 of this embodiment.

  In the wastewater treatment of this embodiment and the comparative example, the wastewater was stirred at room temperature for 24 hours while performing ultraviolet irradiation by the ultraviolet irradiation unit 12. And the nitrate ion density | concentration and nitrite ion density | concentration in the waste_water | drain after a waste_water | drain process were measured.

  As shown in FIG. 2, when the waste water treatment apparatus of this embodiment was used, the nitrate ion concentration after waste water treatment was 130.1 mg / L, and the nitrite ion concentration was 0.8 mg / L. On the other hand, in the comparative example, the nitrate ion concentration after the waste water treatment was 73.6 mg / L, and the nitrite ion concentration was 6.9 mg / L.

  As described above, according to the wastewater treatment apparatus of this embodiment using the nitrate ion conversion material 20 and the nitrite ion conversion material 21, the nitrate ion concentration is slightly higher than that of the comparative example using only the nitrate ion conversion material 20. Although it increased, the nitrite ion concentration could be greatly reduced. That is, according to the waste water treatment apparatus of this embodiment, nitrate ions are reduced by the nitrate ion conversion material 20 to reduce the nitrate ion concentration, and nitrite ions generated as a by-product at that time are oxidized by the nitrite ion conversion material 21. Thus, it can be converted into nitrate ions, and the nitrite ion concentration can be lowered.

  Moreover, in this embodiment, a nitrite ion can be oxidized and converted into a nitrate ion only by making a nitrite ion contact the nitrite ion conversion material 21. Thereby, it is possible to easily reduce the concentration of nitrite ions in the waste water without introducing an organic substance.

  Moreover, in this embodiment, the nitrate ion conversion material 20 and the nitrite ion conversion material 21 are arranged in one wastewater treatment unit 10, and the reduction of nitrate ions and the oxidation of nitrite ions are the same inside the wastewater treatment unit 10. It is done in a container. Thereby, compared with the structure which each performs the reduction | restoration of nitrate ion and the oxidation of nitrite ion with a different container, the structure of a waste water treatment apparatus can be simplified.

(Other embodiments)
As mentioned above, although the Example of this invention was described, this invention is not limited to this, Unless it deviates from the range described in each claim, it is not limited to the description word of each claim, and those skilled in the art Improvements based on the knowledge that a person skilled in the art normally has can be added as appropriate to the extent that they can be easily replaced.

  In the above embodiment, as shown in FIG. 1, the nitrate ion conversion material 20 and the nitrite ion conversion material 21 are arranged in one waste water treatment unit 10, and the reduction of nitrate ions and the oxidation of nitrite ions are performed in the same container. However, the present invention is not limited to this, and the nitrate ion conversion material 20 and the nitrite ion conversion material 21 are disposed in different containers, and nitrate ions are reduced and nitrite ions are oxidized step by step in the respective containers. You may make it perform.

  For example, as shown in FIG. 3, two wastewater treatment units 100 and 101 are provided, the nitrate ion conversion material 20 is disposed in the first wastewater treatment unit 100, and the nitrite ion conversion material 21 is disposed in the second wastewater treatment unit 101. To do. Then, after nitrate ions in the waste water are reduced by the nitrate ion conversion material 20 in the first waste water treatment unit 100, the waste water is moved to the second waste water treatment unit 101, and the second waste water treatment unit 101 converts the nitrite ions. What is necessary is just to oxidize the nitrite ion in waste water with the material 21. FIG. Thus, each process can be reliably performed by performing reduction | restoration of nitrate ion and oxidation of nitrite ion by a different container, respectively. In addition, after the nitrite ion is oxidized in the second wastewater treatment unit 101, if the concentration of nitrate ion in the wastewater becomes too high, the wastewater is returned to the first wastewater treatment unit 100, and the nitrate ion in the wastewater is returned. It is possible to perform reduction again.

  Moreover, in the said embodiment, although the photocatalyst was used as the nitrate ion conversion material 20 which reduces the nitrate ion in waste_water | drain, it is not restricted to this, It is made to reduce nitrate ion in waste_water | drain using materials other than a photocatalyst. Also good.

  Moreover, in the said embodiment, although the nitrate ion conversion material 20 and the nitrite ion conversion material 21 were used in granular form, it is not restricted to this, The nitrate ion conversion material 20 and the nitrite ion conversion material 21 are used in a different form. Also good.

  Moreover, although the said embodiment demonstrated the example which used one type of metal oxide independently as the nitrite ion conversion material 21, not only this but two or more types of metal oxidation as the nitrite ion conversion material 21 was demonstrated. Even when the substances are used at the same time, nitrite ions can be converted into nitrate ions.

  Moreover, in the said embodiment, although the example (refer FIG. 1) which provided the stirring part 11 in the waste water treatment part 10 was demonstrated, not only this but the stirring part 11 may be abbreviate | omitted.

DESCRIPTION OF SYMBOLS 10 Waste water treatment part 20 Nitrate ion conversion material 21 Nitrite ion conversion material 100 1st waste water treatment part 101 2nd waste water treatment part

Claims (12)

  A nitrate ion conversion material (20) capable of reducing nitrate ions in an aqueous solution to an aqueous solution containing at least nitrate ions, and a metal oxide capable of converting nitrite ions in the aqueous solution into nitrate ions A wastewater treatment method comprising contacting the nitrite ion conversion material (21).   The wastewater treatment method according to claim 1, wherein the nitrite ion conversion material is an oxide of one or more metals selected from molybdenum, tungsten, nickel, silicon, and aluminum.   The wastewater treatment method according to claim 2, wherein the nitrite ion conversion material is zeolite.   The wastewater treatment method according to any one of claims 1 to 3, wherein the nitrate ion conversion material is a photocatalyst capable of reducing nitrate ions by ultraviolet irradiation.   The reduction of nitrate ions by the nitrate ion conversion material and the conversion of nitrite ions to nitrate ions by the nitrite ion conversion material are performed in the same container (10). The waste water treatment method as described in any one of these.   The reduction of nitrate ions by the nitrate ion conversion material and the conversion of nitrite ions to nitrate ions by the nitrite ion conversion material are performed in different containers (100, 101), respectively. The waste water treatment method as described in any one of thru | or 4. Wastewater provided with a nitrate ion conversion material (20) capable of reducing nitrate ions in an aqueous solution and a nitrite ion conversion material (21) capable of converting nitrate ions in an aqueous solution into nitrate ions A processing unit (10, 100, 101),
A wastewater treatment apparatus, wherein an aqueous solution containing at least nitrate ions is supplied to the wastewater treatment unit, and the nitrate ion conversion material and the nitrite ion conversion material are brought into contact with the aqueous solution.   The wastewater treatment apparatus according to claim 7, wherein the nitrite ion conversion material is an oxide of one or more metals selected from molybdenum, tungsten, nickel, silicon, and aluminum.   The wastewater treatment apparatus according to claim 8, wherein the nitrite ion conversion material is zeolite.   The wastewater treatment apparatus according to any one of claims 7 to 9, wherein the nitrate ion conversion material is a photocatalyst capable of reducing nitrate ions by ultraviolet irradiation. The nitrate ion conversion material and the nitrite ion conversion material are disposed in the same waste water treatment section (10),
11. The drainage treatment unit performs reduction of nitrate ions by the nitrate ion conversion material and conversion of nitrite ions to nitrate ions by the nitrite ion conversion material. Wastewater treatment equipment described in 1. The nitrate ion conversion material and the nitrite ion conversion material are arranged in different waste water treatment units (100, 101), respectively.
In the wastewater treatment part (100) in which the nitrate ion conversion material is disposed, nitrate ions are reduced by the nitrate ion conversion material, and in the wastewater treatment part (101) in which the nitrite ion conversion material is disposed, The wastewater treatment apparatus according to any one of claims 7 to 10, wherein conversion from nitrite ions to nitrate ions is performed by a nitrite ion conversion material.

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