JP2008200599A - Method for cleaning waste water containing ammonia nitrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cleaning waste water containing ammonia nitrogen, in which a reaction product is used repeatedly in an ammonium magnesium phosphate formation reaction so that it is not necessary to newly replenish a magnesium ion source and a phosphate ion source, which are reactive raw materials. <P>SOLUTION: The method for cleaning waste water containing ammonia nitrogen includes: the first step of mixing the magnesium ion source and the phosphate ion source in the waste water containing ammonia nitrogen to precipitate ammonium magnesium phosphate and subjecting the ammonium magnesium phosphate-precipitated waste water to solid-liquid separation; the second step of bringing hypohalogenate, halogenate or halogen gas into contact with the ammonium magnesium phosphate slurry separated by solid-liquid separation to decompose ammonium magnesium phosphate into magnesium phosphate and nitrogen; and the third step of circulating the magnesium phosphate produced at the second step to the first step to utilize the magnesium phosphate as the magnesium ion source and the phosphate ion source. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for purifying wastewater containing ammonia nitrogen without using biological nitrification denitrification.
More specifically, the present invention relates to a method for purifying waste water containing ammonia nitrogen utilizing a formation reaction of ammonium magnesium phosphate which is a solid.
Furthermore, the waste water containing ammonia nitrogen can be purified without replenishing the magnesium ion source and phosphate ion source of the reaction raw materials by repeatedly using the reaction product in the ammonium magnesium phosphate formation reaction. On how to do.

Wastewater containing ammonia nitrogen components is difficult to be treated by the coagulation sedimentation method and other chemical additions, and biological nitrification denitrification treatment, which is a biological treatment by anaerobic bacteria, is currently performed.
Since the biological treatment method is performed by two steps, a nitrification step for converting ammonia nitrogen to nitrate nitrogen and a denitrification step for converting nitrate nitrogen to nitrogen gas, two different reaction tanks are required. However, since a very long processing time is required, there is a problem that the processing efficiency is extremely poor.

In addition, in this biological treatment method, a large-capacity anaerobic tank is required in order to retain denitrifying bacteria, and there is a problem that the equipment construction cost increases and the installation area of the apparatus increases.
Furthermore, the activity of the denitrifying bacteria is significantly affected by the ambient temperature environment, components contained in the water to be treated, and the like.
Therefore, especially in the winter when the temperature is low, the activity is reduced, and as a result, the denitrification action is lowered and the treatment efficiency becomes unstable.

[Prior art documents]
JP-A-7-284762 Japanese Patent Laid-Open No. 11-10194 JP 2001-104966 A

In addition to this, in recent years, the development of effective and simple treatment methods has increased along with stricter wastewater treatment standards such as the total amount of nitrogen in wastewater being regulated in recent years. Therefore, there is a need for a treatment method that can meet the needs of small-scale wastewater treatment.
For this reason, methods that do not rely on biological treatment have been proposed in recent years, in which both ammoniacal nitrogen and phosphate ions are adsorbed using hydrated iron oxide particles and zeolite particles, and ammoniacal from the wastewater. There is a method of separating and removing both nitrogen and phosphate ions (Patent Document 1).

In this method, hydrated iron oxide particles and zeolite particles, which are adsorbents that adsorb both ammoniacal nitrogen and phosphate ions, are treated with a caustic soda solution to desorb both ammoniacal nitrogen and phosphate ions.
The caustic soda desorption solution containing both ammonia nitrogen and phosphate ions is mixed with a soluble magnesium compound to form a hexahydrate salt of ammonium magnesium phosphate (NH ₄ MgPO ₄ ), which is a solid liquid such as filtration. By separation, magnesium ammonium phosphate is separated and recovered.

The recovered ammonium magnesium phosphate hexahydrate (hereinafter referred to as “MAP”) can be used as a fertilizer containing nitrogen and phosphorus, and this method can be used for wastewater such as sewage. Since it is possible to purify wastewater by removing both ammoniacal nitrogen and phosphate ions contained in various concentrations, and the separated MAP (NH ₄ MgPO ₄ .6H ₂ O) is a valuable component that can be used effectively, The proponent praises it as an excellent purification technology.

However, in order to industrially perform the treatment by this method, there are the following problems.
(1) The operation of taking out the MAP crystal out of the system is complicated, and therefore a large-scale apparatus is required to transport and store the crystal.
(2) The MAP crystal adheres to the inside of the apparatus and is easily scaled, and the maintenance of the apparatus takes time.
(3) Impurities are easily attached to the MAP crystal, so that it is difficult to effectively use it, disposal costs are required, and this method requires a phosphate ion source and a magnesium ion source, and costs are also increased.

Apart from this method, there is also a method in which magnesium salt is added to phosphate ion-containing wastewater, and then biological treatment is performed. In this method, MAP is recovered as a valuable component, but phosphorus compounds contained in wastewater form MAP. Since there are many forms other than the possible orthophosphoric acid, and the production efficiency and recovery efficiency of MAP are low, an improved method has already been proposed (Patent Document 2).
In this improved method, the phosphorus compound in the waste water is converted to normal phosphoric acid by biological treatment before adding the magnesium salt used to form MAP.

In both of this improved method and the above-described adsorption method, phosphate ions used in forming MAP are those contained in the waste water, and ammonium ions and phosphate ions are used to form MAP. However, the amount of phosphate ions contained in the waste water is much smaller than that of ammonium ions.
As a result, in order to sufficiently remove ammonium ions, it is necessary to add an insufficient amount of phosphoric acid to the waste water.

Further, in the improved method, biological treatment is not unnecessary, and in addition to that, facilities for generating MAP, facilities for separation, and the like are required, so that the construction cost of the facilities is not particularly reduced.
Furthermore, the adsorption method uses two types of adsorbents, and the equipment for that is costly, and also requires advanced treatment techniques. In these respects as well, the method is particularly superior to the biological treatment method. I can't say that.

Therefore, a technique for forming and separating and recovering MAP without adding a phosphoric acid component even when a small amount of phosphate ion in the wastewater is not present in an equimolar amount with ammonium ion has already been proposed ( Patent Document 3).
In the method, ammonia and water released from MAP (hereinafter referred to as “H-MAP”) are mixed with ammonium ion-containing waste water to form MAP, and the formed MAP is separated by solid-liquid separation. The separated MAP is heated to release and separate ammonia and water.

As a result, in the method proposed in Patent Document 3, H-MAP and MAP can be repeatedly used for separation and removal of ammonia.
As described above, in this proposed method, the magnesium ion source and the phosphate ion source can be used repeatedly. Once H-MAP is added to the wastewater, the ion source is then added to the wastewater. Is completely unnecessary.

Therefore, the reaction material is introduced into the wastewater from the outside only once at the beginning. After that, there is no need to add any reaction material. The method of repeating the thermal decomposition of MAP is not to use biological treatment. Also excellent in terms.
As described above, the method of repeating the thermal decomposition of MAP is that the decomposition of MAP is thermal decomposition, so the energy consumption is high, and the ammonia generated from the wastewater is generated after the decomposition. Since it is not converted to nitrogen, it is not harmless and non-brominated, and it is difficult to say that it is a sufficient technique in these respects.

Accordingly, the present inventor has eagerly pursued research and development of a technique capable of solving the above disadvantages while taking advantage of the method of repeating the thermal decomposition, and as a result, has succeeded in the development.
That is, the present inventor is surprisingly able to decompose and remove the ammonia component with an oxidizing agent such as hypohalous acid even in the crystalline state in the process of separating the MAP crystal and studying its decomposition method. The present invention was completed by finding the facts and utilizing the findings.

Therefore, the present inventor should solve the problem of the present invention by providing a method for purifying wastewater containing ammonia nitrogen, which can eliminate the disadvantages described above, while taking advantage of the method of repeating the thermal decomposition. It is to be an issue.
That is, the present invention separates and removes ammonia nitrogen in wastewater as MAP, and in this case, decomposition of MAP while taking advantage of the ability to repeatedly use a magnesium ion source and a phosphate ion source. It is an object of the present invention to provide a method for purifying wastewater containing ammonia nitrogen that can be decomposed to nitrogen without using thermal decomposition and without generating ammonia after decomposition of MAP.

  The present invention provides a method for purifying wastewater containing ammonia nitrogen for achieving the above object, which comprises mixing phosphoric acid by mixing a magnesium ion source and a phosphate ion source with wastewater containing ammonia nitrogen. First step of depositing ammonium magnesium and solid-liquid separation, contacting ammonium hypohalite or halogen gas to the ammonium magnesium phosphate slurry after solid-liquid separation to decompose ammonium magnesium phosphate to form magnesium phosphate and nitrogen And a third step of circulating the magnesium phosphate produced in the second step to the first step and using it as a magnesium ion source and a phosphate ion source.

And as for the purification processing method of the waste_water | drain containing the ammonia nitrogen, the following is preferable.
(1) The magnesium ion source to be mixed in the wastewater is 1.5 to 1 in terms of the molar ratio of magnesium to nitrogen, and the phosphate ion source is in the range of 1 to 1 in terms of the molar ratio of phosphorus to nitrogen.
That is, regarding the addition amount of both ion sources, a magnesium source is 1.5 mol or more per 1 mol of nitrogen, and a phosphate ion source is 1 mol or less per 1 mol of nitrogen.
(2) The solid-liquid separation in the first step is sedimentation separation, and the ammonium magnesium phosphate slurry in the second step is a slurry obtained by sedimentation separation.
(3) The solid-liquid separation in the first step is filtration or centrifugation, and the ammonium magnesium phosphate slurry in the second step is obtained by adding raw water or purified water to the ammonium magnesium phosphate after solid-liquid separation. Be formed
(4) The hypohalite is sodium hypochlorite, calcium hypochlorite, magnesium hypochlorite or a mixture thereof.
(5) The halide salt is sodium chlorate, calcium chlorate, potassium chlorate, magnesium chlorate or a mixture thereof.
(6) The halogen gas is chlorine gas

  In the method for purifying wastewater containing ammonia nitrogen of the present invention, ammonium magnesium phosphate is formed, and magnesium phosphate produced by decomposing this is used as a magnesium ion source and a phosphate ion source. As a result, since the magnesium ion source and the phosphate ion source can be used repeatedly, the magnesium ion source and the phosphate ion source need only be added to the waste water once, and then the magnesium ion source and phosphate ion are newly added. MAP can be formed without adding a source.

In the present invention, the formed MAP can be decomposed by bringing a hypohalite, a halogenate or a halogen gas into contact with the slurry, and the MAP proposed in Patent Document 3 is decomposed by thermal decomposition. Thermal energy can be reduced compared to the case.
Furthermore, in the method of the present invention, MAP is not decomposed and produced by ammonia, but is odorless and harmless nitrogen. Like the ammonia produced when MAP proposed in Patent Document 3 is decomposed by thermal decomposition. Therefore, there is an advantage that no further detoxification treatment is required.

  In the following, embodiments including the best mode for carrying out the present invention will be described in detail with reference to FIGS. 1 and 2, but the present invention is not limited in any way by these embodiments. Needless to say, it is specified by the scope of claims.

  As described above, the present invention includes a first step of mixing a magnesium ion source and a phosphate ion source in a wastewater containing ammonia nitrogen to precipitate ammonium magnesium phosphate and performing solid-liquid separation, and ammonium magnesium phosphate after solid-liquid separation. A second step of bringing the slurry into contact with a hypohalite, a halogenate or a halogen gas to decompose ammonium magnesium phosphate to form magnesium phosphate and nitrogen, and the magnesium phosphate produced in the second step is the first. It is characterized by including a third process which is circulated in the process and used as a magnesium ion source and a phosphate ion source.

In this wastewater purification process, there are ammonium magnesium phosphate formation reaction, ammonium magnesium phosphate decomposition reaction with hypohalite (halogenate), and halogen gas decomposition reaction. It is as follows.
[Production reaction of ammonium magnesium phosphate]
NH ₄ ⁺ + Mg ²⁺ + PO ₄ ^3- → NH ₄ MgPO ₄ ↓ (Formula 1)
[Decomposition reaction with hypochlorous acid]
NH ₄ MgPO ₄ + 3HClO → 1 / 2N ₂ ↑ + 3Cl ⁻ + 1 / 3Mg ₃ (PO ₄ ) ₂ ↓
+ 1 / 3H ₃ PO ₄ + 3H ₂ O (Formula 2)
[Decomposition reaction with chlorine gas]
NH ₄ MgPO ₄ + 3 / 2Cl ₂ →
1 / 2N ₂ ↑ + 3HCl + 1 / 3Mg ₃ (PO ₄ ) ₂ ↓ + 1 / 3H ₃ PO ₄ (Formula 3)

In the present invention, for the magnesium ion source compound initially added to the wastewater, various compounds can be used without any particular limitation as long as the compound can be dissolved in the wastewater to produce Mg ²⁺ . For example, magnesium carbonate, magnesium chloride, magnesium sulfate, magnesium hydroxide, magnesium oxide, etc. can be exemplified, but since the anion is carbonate ion, anion that is not originally contained in the wastewater is newly generated after dissolution. Magnesium carbonate is preferable in that it does not occur.

  Furthermore, the phosphate ion source compound that is first added to the wastewater is not particularly limited as long as it is a compound that can be dissolved in the wastewater to generate phosphate ions, and various compounds can be used. Can be exemplified by normal phosphoric acid, sodium phosphate, sodium hydrogen phosphate, magnesium phosphate, calcium phosphate, etc., but handling properties, cations are hydrogen ions, so cations that are not originally contained in wastewater after dissolution Orthophosphoric acid is preferable in that it is not newly generated.

A magnesium ion source compound such as basic magnesium carbonate and a phosphate ion source compound such as phosphoric acid are mixed with waste water, and the magnesium ion source mixed in the waste water has a molar ratio of magnesium to nitrogen of 1.5 or more and 1: 1. The phosphate ion source is preferably not more than 1: 1 in terms of a molar ratio of phosphorus to nitrogen.
That is, regarding the addition amount of both ion sources, it is preferable that a magnesium source is 1.5 mol or more with respect to 1 mol of nitrogen, and a phosphate ion source is 1 mol or less with respect to 1 mol of nitrogen.
Moreover, although it is good to add both compounds to waste_water | drain at the time of the mixing, the reverse may be sufficient.
Furthermore, at the time of the addition, both compounds may remain in a solid state or may be in a slurry state by adding water.

[Embodiment 1]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2. First, a diagram illustrating a form in which sedimentation separation is used for solid-liquid separation of MAP (hereinafter, may be abbreviated as “Embodiment 1”). 1 will be described in detail.
In the first embodiment, basic magnesium carbonate and phosphoric acid are first added to wastewater containing ammonia nitrogen while stirring, then a caustic soda solution is added, and after the addition, the mixture is allowed to stand for about 10 minutes to 3 hours. In that case, stirring should be continued.

The addition of the caustic soda solution is because the phosphate ion source compound is phosphoric acid, and as a result, the pH is extremely lowered. If the compound is a phosphate, there is no extreme pH drop. No special addition is required.
As described above, when an aqueous sodium hydroxide solution (caustic soda solution) is added, it should be allowed to stand for a period of time after the addition, and the concentration of the aqueous sodium hydroxide solution should be about 5 to 50%. Is preferably about 8 to 9, particularly preferably around 8.
Even when no sodium hydroxide aqueous solution is added, it is preferable to leave it for the above time.

After this standing, the MAP is separated from the waste water, and since the MAP is obtained as a slurry, the separation is preferably performed by sedimentation separation as in the first embodiment, because the reason is that the MAP is slurried. It is because it is excellent in contact property and reactivity with sodium hypochlorite or chlorine gas used for the decomposition reaction.
For separation of MAP, sedimentation separation is preferable as described above, but various other solid-liquid separation means can be used without particular limitation, and examples thereof include sedimentation separation, filtration, and centrifugation. it can.
In addition, when the MAP is not slurried by solid-liquid separation by means other than sedimentation separation, it may be slurried by adding raw water or drained water to the separated MAP.

For sodium hypochlorite or sodium chlorate used for the MAP decomposition, if it is an alkali hypohalite or alkali halide having the ability to decompose MAP in water and generate nitrogen, Various types can be used without being limited to sodium hypochlorite or sodium chlorite, and include magnesium hypochlorite, calcium hypochlorite, potassium hypochlorite, sodium hypobromite, chlorine. Examples thereof include potassium acid, calcium chlorate, and magnesium chlorate.
Further, the chlorine gas is not particularly limited, and various types of chlorine gas can be used as long as they are capable of decomposing MAP in water and generating nitrogen. Examples thereof include fluorine, bromine, and iodine.

After the sodium hypochlorite aqueous solution is added to the MAP slurry, it is allowed to stand for a predetermined time, after which MAP decomposes and newly solids settle, but the newly produced solids are magnesium phosphate. .
The concentration of the sodium hypochlorite aqueous solution should be 3-15% of effective chlorine, and the standing time should be set to an optimum time considering the operating temperature, oxidant concentration, etc. Is good.
Since the newly produced solid magnesium phosphate becomes a magnesium ion source and a phosphate ion source, it is added to the waste water.
Thereby, it can be repeatedly used as a magnesium ion source and a phosphate ion source without newly using basic magnesium carbonate and phosphoric acid.

[Embodiment 2]
Next, an embodiment in which filtration is used for solid-liquid separation of MAP (hereinafter may be abbreviated as “Embodiment 2”) will be described in detail with reference to FIG.
As in the case of Embodiment 1, first, basic magnesium carbonate and phosphoric acid are added to wastewater containing ammonia nitrogen while stirring to produce MAP. The adoption of an aqueous sodium hydroxide solution and the pH after the addition when it is adopted are the same as in the first embodiment.

The generated MAP is separated from the waste water by filtration, but this is only different from the first embodiment, and the others are preferably the same as in the first embodiment.
The MAP separated due to this difference has no accompanying water unlike the case of sedimentation separation, so it is slurried by adding water (raw water or drained water is good) and then for MAP decomposition. Halogen gas such as chlorine gas or hypohalous acid alkali salt such as sodium hypochlorite is added, and the other points may be the same as in the first embodiment.

2.7 g of basic magnesium carbonate (about 45% as MgO) and 2.8 g of 85 w% phosphoric acid were added to 350 mL of waste water containing 976 milligrams (mg) / liter (L) of ammonia nitrogen.
Since the pH after addition of phosphoric acid was about 2.5 and acidic, a 20% aqueous sodium hydroxide solution was added with stirring at 25 ° C. in a thermostatic bath to adjust the pH to 8.8.

After the adjustment, the liquid temperature was maintained for about 1.5 hours and stirring was continued, and then the precipitated solid content was allowed to settle and the composition of the supernatant liquid was analyzed.
The composition was 132 mg / L for ammonia nitrogen as N, 260 mg / L for magnesium, and 27 mg / L for phosphorus.
The precipitated solid was white crystals with good sedimentation, and the composition thereof was 4.95% as N for ammonia nitrogen, 10.9% for magnesium, and 13.7% for phosphorus.

Next, 280 mL of the supernatant is separated, 350 mL of an aqueous sodium hypochlorite solution containing about 5% effective chlorine is added to the slurry containing the remaining solid, and the volume is made up to 550 mL with demineralized water. After stirring for about 4 hours, the solid content was allowed to settle.
The composition of the supernatant at this time was ammonia nitrogen N of less than 0.1 mg / L, magnesium 35 mg / L, and phosphorus 766 mg / L.
The composition of the solid content was 0.08% as N for ammonia nitrogen, 5.5% for magnesium, and 7.1% for phosphorus. Next, the slurry containing solid content from which ammonia nitrogen was decomposed and removed was repeatedly used for treatment of waste water containing ammonia nitrogen.

Magnesium chloride (hexahydrate) (13.89 g) and 85 w% phosphoric acid (5.94 g) were added to 200 mL of wastewater containing 4653 mg / L of ammonia nitrogen as N and 612 mg / L of organic substances mainly composed of formic acid as COD.
Since the pH after addition of phosphoric acid was 2.33, the pH was adjusted to 8.7 by adding an aqueous sodium hydroxide solution while stirring at 25 ° C. in a thermostatic bath.
After the adjustment, the liquid temperature was maintained for about 1.5 hours and stirring was continued, and then the precipitated solid content was subjected to suction filtration.

The amount of the filtrate obtained by the above experimental operation was 218 mL, and the composition was 1310 mg / L of ammonia nitrogen as N, COD of 485 mg / L, magnesium of 1380 mg / L, and phosphorus of less than 5 mg / L.
Further, the weight (undried) of the solid content was 25.5 g, and the composition thereof was 1.71% as ammonia nitrogen as N, 4.95% as magnesium, and 6.2% as phosphorus.

Next, the solid content was added to 350 ml of a sodium hypochlorite aqueous solution of about 5% effective chlorine added to dehydrated water and stirred for about 4 hours at 25 ° C. in a thermostatic bath, followed by filtration.
The amount of the filtrate obtained by the above experimental operation was 458 mL, and the composition thereof was ammonia nitrogen N less than 0.1 mg / L, magnesium 190 mg / L, and phosphorus 690 mg / L.
Further, the weight (undried) of the solid content was 20.3 g, and the composition was 0.1% ammonia nitrogen as N, 6.6% magnesium, and 7% phosphorus.
Next, the solid content from which ammonia nitrogen was decomposed and removed was repeatedly used for treatment of ammonia nitrogen-containing waste water.

Embodiment 1 of the present invention is illustrated. Embodiment 2 of the present invention is illustrated.

Claims (7)

  First step of mixing magnesium ion source and phosphate ion source into waste water containing ammonia nitrogen to precipitate ammonium magnesium phosphate and solid-liquid separation, hypohalite to ammonium magnesium phosphate slurry after solid-liquid separation A magnesium ion source in which a magnesium salt phosphate or halogen gas is contacted to decompose ammonium magnesium phosphate to form magnesium phosphate and nitrogen, and the magnesium phosphate produced in the second step is circulated to the first step. And a method for purifying wastewater containing ammonia nitrogen, comprising a third step utilized as a phosphate ion source.   2. The ammonia state according to claim 1, wherein the magnesium ion source mixed in the waste water has a magnesium to nitrogen molar ratio of 1.5 or more and 1 and the phosphate ion source has a phosphorus to nitrogen molar ratio of 1 or less to 1. A method for purifying wastewater containing nitrogen.   The solid-liquid separation in the first step is sedimentation separation, and the ammonium magnesium phosphate slurry in the second step is a slurry obtained by sedimentation separation. Purification of waste water containing ammonia nitrogen according to claim 1 or 2 Processing method.   The solid-liquid separation in the first step is filtration or centrifugation, and the ammonium magnesium phosphate slurry in the second step is formed by adding water to the ammonium magnesium phosphate after solid-liquid separation. A method for purifying wastewater containing ammonia nitrogen according to 1 or 2.   The method for purifying wastewater containing ammonia nitrogen according to claim 4, wherein the water is raw water or purified water.   The purification of waste water containing ammonia nitrogen according to any one of claims 1 to 5, wherein the hypohalite is sodium hypochlorite, calcium hypochlorite, magnesium hypochlorite or a mixture thereof. Processing method.   The method for purifying waste water containing ammonia nitrogen according to any one of claims 1 to 5, wherein the halogen gas is chlorine gas.

Images