JPH11239785A - Agent and method for simultaneously removing nitrogen and phosphorus from wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously efficiently inexpensively remove nitrogen and phosphorus from wastewater by constituting zeolite mainly of magnesium-substituted zeolite in which at least a part of sodium ions and calcium ions in zeolite is substituted with magnesium ions. SOLUTION: Natural, synthetic, or artificial zeolite is pulverized to be mixed and brought into contact with a magnesium chloride solution at the temperature equal to or higher than room temperatures, and then the solution is filtered to be removed. By this operation, sodium and calcium ions in the zeolite is substituted preferentially with magnesium ions to form magnesium-substituted zeolite. The amount substituted with the magnesium ions in this magnesium- substituted zeolite is preferably adjusted to have a cation exchange capacity of zeolite, before substitution, of 10% or higher. The use of natural seawater (normally containing about 5500 mg/l of magnesium chloride) can remarkably reduce the treatment cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simultaneous removal agent and a simultaneous removal method of nitrogen and phosphorus from wastewater, and more particularly, to a method of replacing some components of zeolite ions with other ions. This is a technology that removes nitrogen and phosphorus from domestic wastewater such as sewage.

[0002]

2. Description of the Related Art In recent years, in urban areas where the population is concentrated, the water environment deteriorates due to domestic wastewater such as sewage, and especially, rivers, lakes and marshes and closed sea areas due to nitrogen and phosphorus contained in the domestic wastewater. Water pollution, such as eutrophication, has become a problem, and its prevention and improvement has become a major issue.

[0003] By the way, at present, such domestic wastewater is discharged into public waters after being treated in a purification facility such as a sewage treatment plant. However, according to a standard treatment method, 15 to 20 mg of nitrogen is still discharged during discharge. / L, about 2-5mg of phosphorus
Per liter. From the viewpoint of environmental conservation, it is desirable that each of them is 1/10 or less. Therefore, conventionally, reduction has been attempted by using an "anaerobic-anoxic-aerobic method", an "adsorption method", a "coagulation-sedimentation method" or the like described later.

[0004] However, the "anaerobic-anoxic-aerobic method"
In a biological treatment method using bacteria such as that described above, nitrogen is removed only up to about 10 mg / l and phosphorus up to about 1 mg / l. It was necessary to use the method together with the "adsorption method" using a metal salt or the "aggregation precipitation method" using a metal salt of iron, aluminum, calcium or the like as an aggregating agent.

[0005] In addition, such "adsorption method" and "coagulation sedimentation method"
All of the physicochemical treatment methods such as above treat nitrogen or phosphorus alone, and it is necessary to set conditions (for example, pH in a used solution) suitable for each treatment. Is complicated. That is, in the case of domestic wastewater, nitrogen generally exists as a cation in an ammonia state, and phosphorus exists as an anion in an orthophosphate state. Therefore, in order to remove both of these, conventionally, it was necessary to perform the treatment in two stages by different treatment methods. In addition, in any of the treatment methods, addition of an acid or an alkali is indispensable in order to optimize the pH of the solution to be used, and finally, a neutralization treatment must be performed.
As a result, the water after the treatment contains inorganic salts, and there is a problem that there is a restriction on the reuse or an increase in the amount of generated sludge.

[0006] In order to simplify such a complicated wastewater treatment step, zeolite substituted and modified with calcium, aluminum, nickel, silver and iron ions has been conventionally used, and ammonium ion and orthotrin in an aqueous solution have been used. Techniques for simultaneously removing acid ions have been studied. Then, the iron-substituted zeolite was subjected to an ammonium ion concentration of 1
When added to water containing 0 mg / l (7.77 mg / l as nitrogen) and 10 mg / l orthophosphate ion concentration (3.26 mg / l as phosphorus), the effect of removing those ions is greatest, and ammonium ion 85% and 40% of the orthophosphate ions were reported at a zeolite research conference in 1993.

However, in this technique, the removal rate of orthophosphate ions is as low as 40%, and there is a feeling of being one step closer to practical use as a simultaneous removal agent with ammonia ions.

[0008]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method for efficiently removing nitrogen and phosphorus from domestic wastewater,
It is an object of the present invention to provide a simultaneous removing agent which can be removed at low cost, and a simultaneous removing method using the removing agent.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventors have made intensive studies focusing on the cation adsorption capacity and chemical structure of zeolite. As a result, if the zeolite modified by replacing the cations of some of the constituent elements constituting the zeolite with ions of a specific element is added to the wastewater, the ammonium ions in the wastewater will be adsorbed by the zeolite, while The present inventors have found that phosphate ions form hardly soluble salts with the specific element ions released from the zeolite, and that solid salts can be removed by solid-liquid separation, thus completing the present invention.

That is, the present invention provides a method for removing nitrogen and phosphorus from wastewater, comprising a magnesium-substituted zeolite obtained by substituting at least part of sodium ions and potassium ions in zeolite with magnesium ions. It is a simultaneous removal agent. Further, the present invention provides the magnesium-substituted zeolite, wherein the substitution amount of magnesium ions is one of the cation exchange capacity of the zeolite before substitution.
It is a simultaneous removal agent for nitrogen and phosphorus from wastewater, characterized in that it is 0% or more.

Further, the present invention is the agent for simultaneously removing nitrogen and phosphorus from wastewater, wherein the source of magnesium ions is seawater. In addition, the present invention, the particle size of the zeolite 200μm or less,
Alternatively, the present invention is an agent for simultaneously removing nitrogen and phosphorus from wastewater, wherein the zeolite is an artificial zeolite using coal ash or sewage sludge incineration ash as industrial waste as a raw material.

In addition, the present invention provides a method for removing nitrogen and phosphorus contained in wastewater by adding a chemical to the above-mentioned co-removing agent, and removing ammonium ions contained in the wastewater by the magnesium. -At the same time as adsorbing to the zeolite in exchange for ions, the magnesium ions released from the zeolite are reacted with ortho-phosphate ions contained in the wastewater to form hardly soluble magnesium phosphate, A method for simultaneous removal of nitrogen and phosphorus from wastewater, comprising removing solid-liquid separation of zeolite to which a soluble phosphate and ammonium ions are adsorbed.

The present invention also provides a method for simultaneously removing nitrogen and phosphorus from waste water, wherein the solid-liquid separation is performed by membrane separation. The wastewater in the present invention includes not only domestic wastewater and factory wastewater but also so-called treated water after purifying them once. According to the present invention, nitrogen and phosphorus contained in the wastewater can be simultaneously removed from the wastewater contained in one reaction tank using the same type of chemicals, so that the wastewater can be treated more efficiently than in the past. Becomes possible. Further, in the present invention, since an artificial product is used as the zeolite or the supply source of magnesium ions is seawater, the wastewater can be treated at a much lower cost than before.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The simultaneous removal agent for nitrogen and phosphorus from wastewater according to the present invention (hereinafter, simply referred to as a simultaneous removal agent) is one in which at least one of sodium ion and potassium ion in zeolite is magnesium ion. The main component is a magnesium-substituted zeolite obtained by substitution.

[0015] First of all, the raw material of zeolite, which is also referred to as zeolite, the general formula _{M 2 / n O · Al 2} O 3 · xSiO 2 · yH 2
It has a chemical composition represented by O. Where M is N
a and K are alkaline metal elements or alkaline earth metal elements such as Ca and Ba, n is their valence (1 or 2), x is 2-10, and y is 2-7. The molecular structure of a zeolite having such a composition is (Al, S
i) A structure in which alkali metal ions and / or alkaline earth metal ions and water molecules are contained in pores in a three-dimensional network formed by tetrahedrons sharing vertices. Therefore, in general, zeolite is mainly replaced by sodium ions or potassium ions contained therein,
Cations (for example, ammonium
Ion).

Typical zeolites represented by the above general formula include mesolite, chabazite, goethite, sodalite,
Examples include mordenite, pyroxene, bouillite, turbidite, zeolite A, zeolite X, and zeolite Y. They occur naturally in fissures and cavities in basic volcanic rocks, hydrothermal alterations, tuffs, marine sediments, and are found in low-grade metamorphic rocks. In addition, these natural zeolites and clay minerals are used as raw materials for industrial synthesis and used as molecular sieves, catalysts, adsorbents, water treatment agents, soil conditioners, paper fillers, and the like. In recent years, artificial zeolites made from waste materials such as coal ash, sewage sludge incineration ash, municipal waste incineration ash, and paper sludge have also been manufactured.

The simultaneous removal agent for nitrogen and phosphorus according to the present invention comprises:
Using such a zeolite, it is manufactured as follows. That is, the above-mentioned natural zeolite, synthetic zeolite or artificial zeolite is pulverized, mixed with a magnesium chloride aqueous solution at a temperature of room temperature or higher, brought into contact, and then the aqueous solution is removed by filtration. By this operation, sodium ions and potassium ions in the zeolite become
It is preferentially replaced by magnesium ions to form the magnesium-substituted zeolite described above. The replacement with magnesium ions was performed much more quickly than the replacement with calcium ions and the like described above.

In the present invention, the zeolite used is preferably ground to a particle size of 200 μm or less.
This is because the replacement rate of magnesium ions increases, and the replacement is promoted. Furthermore, for the same reason, the magnesium chloride concentration in the aqueous magnesium chloride solution is 0.02
It is preferable that the content be 1904 mg or more per mol / liter, that is, the content per liter. In this case, if natural seawater (usually containing about 5500 mg / liter of magnesium chloride) is used as the aqueous magnesium chloride solution, the processing cost can be significantly reduced.

In the present invention, the replacement amount of magnesium ion of the nitrogen- and phosphorus-removing agent containing magnesium-substituted zeolite obtained as a main component is determined by the cation exchange capacity (CEC, Cation Exchange Capacity) of the zeolite before substitution.
(Abbreviation of Capacity) is preferably 10% or more. The cation exchange capacity is the total amount of cation exchange per unit amount of the ion exchanger. For example, when the CEC of the zeolite before substitution is 200 meq / 100 g, the replacement amount of magnesium ion is 20 meq / 100 g or more, that is, the MgO content is 0.40% or more, which is larger than that of the zeolite before substitution. It is. If the replacement amount of magnesium ions is less than 10%, the effect of removing ammonium ions in water is not affected, but the efficiency of removing orthophosphate ions decreases. Next, an embodiment of the method for simultaneously removing nitrogen and phosphorus from wastewater according to the present invention will be described.

It is to add a simultaneous removal agent of nitrogen and phosphorus (hereinafter also referred to as a chemical) containing magnesium-substituted zeolite as a main component to waste water containing ammonium ions and orthophosphate ions. Through this addition, ammonium ions in the wastewater are exchanged for magnesium ions and adsorbed on zeolite,
The magnesium ions released from the zeolite react with the orthophosphate ions in the wastewater to produce magnesium phosphate which is hardly soluble in water. Therefore, ammonium
If the solids such as zeolite and magnesium phosphate to which the ions are adsorbed are separated by filtration, nitrogen and phosphorus in the wastewater can be temporarily removed only by using one reaction tank. The magnesium ion and the hydrogen phosphate ion usually react rapidly to form hardly soluble magnesium hydrogen phosphate (MgHPO ₄ .3H ₂ O).

Therefore, the wastewater to which the simultaneous removal method according to the present invention is applied needs to coexist with ammonium ions in addition to orthophosphate ions. Even if the agent containing magnesium-substituted zeolite as a main component is added to water containing only orthophosphate ions, only a small amount of orthophosphate ions is removed. This is because magnesium ions are hardly released from the zeolite.

In practicing the present invention, the amount of the co-removing agent containing magnesium-substituted zeolite as a main component in the waste water is determined in consideration of the concentration of orthophosphate ions in the waste water and the amount of magnesium ion substituted in the removing agent. Need to decide. For example, an ammonia nitrogen concentration of 20 m
g / l, phosphoric acid phosphorus concentration: 2.0 mg / l When the secondary effluent of sewage is treated by the simultaneous removal method according to the present invention at a treatment amount of 10 m ³ / hour, the inflow of phosphoric acid phosphorus Is 20 g / h (= 1.29 eq / h, (HPO ₄
^{Since 2-} ))), when using simultaneous removal (drug) with a magnesium ion replacement amount of 20 meq / 100 g, setting the nitrogen concentration to 0 requires a required addition amount of 6.46 kg / drug. It will be over time.

Lastly, an embodiment of the method for simultaneously removing nitrogen and phosphorus from wastewater according to the present invention described above is shown in FIG.
This will be described based on the conceptual diagram shown in FIG. First, waste water 1 containing ammonium ions and orthophosphate ions is led to a chemical addition tank 2 where a predetermined amount of a co-removing agent 3 mainly composed of magnesium-substituted zeolite is added by the above-described method. The wastewater 1 to which the simultaneous removing agent 3 has been added is transferred to a reaction tank 5 having a stirring device 4 and is stirred for a certain time. Thereafter, a membrane separation device 6 composed of an ultrafiltration membrane or a microfiltration membrane module is immersed in the wastewater in the reaction tank 5, and solid-liquid separation is performed using a suction pump 7. The reason why a membrane separation device is used as the device for performing solid-liquid separation of the present invention is that water containing no solids 8 can be obtained as the membrane-permeated water 9, which is preferable. Further, if the simultaneous removal agent 3 is continuously or intermittently added to the wastewater 1, the concentration of the solids 8 such as the hardly soluble phosphates generated increases, and they are accumulated in a large amount in the reaction tank 5. I do. Therefore, in FIG. 1, in order to continuously or intermittently extract the solid content 8, a solid content extraction device 10 by centrifugation or the like is provided.

[0024]

(Example 1) As a raw material zeolite, a natural zeolite "Otaniishi" from Otani, Tochigi Prefecture was used to produce the simultaneous removing agent according to the present invention. Table 1 shows the chemical components of "Oyaishi". First of all, this stone has a maximum particle size of 2
It was pulverized to an average diameter of 87 μm with a diameter of not more than 00 μm and sieved to prepare a fine powder. When the cation exchange capacity (CEC) of this fine powder was examined, it was found to be 260 meq / 100 g.
Met. Subsequently, 15 g of this fine powder was mixed with a magnesium chloride content of 3917 mg / liter (0.041 mg / liter).
(Mole / liter) and 200 ml aqueous solution of magnesium chloride at a temperature of 30 ° C., and then the mother liquor was extracted and removed. Then, the operation of newly mixing and contacting the residue with an aqueous solution of magnesium chloride of the same concentration under the same conditions was repeated three times, and the finally obtained residue was used as a simultaneous removing agent mainly containing magnesium-substituted zeolite. This remover had a 0.98% increase in MgO content over the raw material zeolite, which was 81.6 meq / 100 g in terms of magnesium ion replacement.
31.4% of the cation exchange capacity (CEC)
Is equivalent to

[0025]

[Table 1]

Next, the effect of this simultaneous removing agent was confirmed.
100 ml of water containing 5.0 mg / l of ammonium ion (3.88 mg / l as nitrogen) and 1.0 mg / l of orthophosphate ion (0.33 mg / l as phosphorus) were added.
Individual containers were prepared. Then, in the water in these containers, 0.1 g, 0.5 g,
g, 2.0 g of ammonium monium in the supernatant.
The change in the concentration of ions and orthophosphate ions was examined over one hour. As a result, 40 minutes after the addition of the drug, the concentration of the ions remaining in the aqueous solution became constant, indicating that the reaction was completed.

Table 2 shows the concentrations of ammonium ions and orthophosphate ions before and 1 hour after the addition of the drug. From Table 2, the effect of the simultaneous removal agent according to the present invention is clear. In particular, when 2 g is added, the removal rate of both ions exceeds 80% or more. This result indicates that the efficiency of removing orthophosphate ions is greatly improved as compared with the case where the conventional simultaneous removal agent containing calcium-substituted zeolite as a main component is used.

[0028]

[Table 2]

Example 2 Ammonium ion was added to 10
mg / L (7.77 mg / L as nitrogen) and wastewater containing 2.0 mg / L of orthophosphate ions (0.65 mg / L as phosphorus), as in Example 1, 100 mm each in three containers. -In a liter, 0.1 g, 0.5 g and 2.0 g of the same co-removing agent used in Example 1 were added, respectively. in this case,
Thirty minutes after the addition of the chemical, the residual ion concentration in the wastewater became constant. Table 3 shows the concentrations of ammonium ion and orthophosphate ion before and 1 hour after the addition of the drug. Table 3
Thus, the effect of the simultaneous removal agent according to the present invention is clear.
In particular, by adding 2 g, both ion removal rates are 90%.
More than that.

[0030]

[Table 3]

Example 3 Ammonium ion was added to 30
Example 1 were placed in three containers each containing 100 ml of wastewater containing mg / liter (23.3 mg / liter as nitrogen) and 6.0 mg / liter of orthophosphate ions (1.96 mg / liter as phosphorus). 0.1 g, 0.5 g, 2.0 g of the same co-remover used
g, and the change in the ion concentration with time until one hour later was examined. Also in this case, the residual ion concentration of the wastewater became constant 30 minutes after the addition of the chemical. Table 4 shows the concentrations of ammonium ion and orthophosphate ion before and 1 hour after the addition of the drug. From Table 4, the effect of the simultaneous removal agent according to the present invention is clear. In particular, when 2 g is added, the removal rate of both ions is high.

[0032]

[Table 4]

[0033]

As described above, according to the present invention, ammonium ions and orthophosphate ions in domestic wastewater and primary treatment water thereof can be simultaneously and efficiently removed. As a result, it becomes possible to reuse water obtained by purifying domestic wastewater at a lower cost than before.

The simultaneous removal of nitrogen and phosphorus according to the present invention is economically advantageous because not only expensive synthetic zeolites but also inexpensive natural and artificial zeolites can be used as raw zeolites. In particular, when the artificial zeolite is coal ash, sewage sludge incineration ash, or the like, effective use of waste can be achieved. Furthermore, the solids discharged by the simultaneous removal method according to the present invention, zeolite has already been approved as a soil conditioner by the Ministry of Agriculture, Forestry and Fisheries, and magnesium phosphate has been used as a phosphate fertilizer. Can also be returned to soil, which can contribute to the construction of a zero-emission waste treatment system expected by the public.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an apparatus for implementing a method for simultaneously removing nitrogen and phosphorus from wastewater according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Drainage 2 Chemical addition tank 3 Simultaneous remover of nitrogen and phosphorus from wastewater (simultaneous remover) 4 Stirrer 5 Reaction tank 6 Membrane separator 7 Suction pump 8 Solid content 9 Membrane permeated water 10 Solid content extraction device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/42 C02F 1/42 F 1/44 1/44 E 1/58 1/58 PR

Claims (7)

[Claims] 1. A simultaneous removal agent for nitrogen and phosphorus from wastewater, comprising a magnesium-substituted zeolite obtained by substituting at least a part of sodium ions and potassium ions in zeolite with magnesium ions as a main component. 2. The simultaneous replacement of nitrogen and phosphorus from wastewater according to claim 1, wherein the magnesium-substituted zeolite has a magnesium ion substitution amount of 10% or more of the cation exchange capacity of the zeolite before substitution. Remover. 3. The agent for simultaneously removing nitrogen and phosphorus from wastewater according to claim 1, wherein the supply source of the magnesium ions is seawater. 4. The agent for simultaneously removing nitrogen and phosphorus from wastewater according to claim 1, wherein the zeolite has a particle size of 200 μm or less. 5. The nitrogen and phosphorus from wastewater according to claim 1, wherein the zeolite is an artificial zeolite made from coal ash or sewage sludge incineration ash as industrial waste. Simultaneous remover. 6. A method for removing nitrogen and phosphorus contained in waste water by adding a chemical thereto, wherein the chemical remover according to claim 1 is used to remove ammonium ions contained in the waste water. The magnesium ions released from the zeolite are simultaneously reacted with the ortho-phosphate ions contained in the waste water to form hardly soluble magnesium phosphate by exchanging the magnesium ions with the zeolite. A method for simultaneously removing nitrogen and phosphorus from waste water, wherein the zeolite and the hardly soluble phosphate adsorbed with the ammonium ion are removed by solid-liquid separation. 7. The method for simultaneously removing nitrogen and phosphorus from wastewater according to claim 6, wherein the solid-liquid separation is performed by membrane separation.