JPH11277071A - How to remove phosphorus - Google Patents

Abstract

(57) Abstract: In a dephosphorization method in which raw water flows upward to a reaction tower and MAP particles are separated and recovered from a lower part of the reaction tower, the phosphorus concentration in the treated water is made to be extremely low. SOLUTION: Raw water is supplied to a lower part of a reaction tower 1 and treated water is taken out from an upper part of the reaction tower 1 and a part of the treated water is circulated to a lower part of the reaction tower 1 to generate MAP particles.
Remove from the bottom. 3 by molar ratio of phosphorus in raw water
More than twice the magnesium salt and ammonium salt
To supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing phosphorus in phosphorus-containing water as MAP (magnesium ammonium phosphate), and more particularly to a method for removing phosphorus which can obtain treated water having a low phosphorus concentration.

[0002]

2. Description of the Related Art As a method for removing phosphorus from phosphorus-containing water such as sludge dewatered filtrate and digestion desorbed liquid generated in anaerobic and aerobic treatment processes such as sewage, human waste, and wastewater, magnesium salts or water are added to phosphorus-containing water. There is a method in which magnesium oxide is added, MAP is generated from the ammonia component and phosphorus and magnesium components contained in the water, and the generated MAP particles are separated.

In the conventional phosphorus removal method (phosphorus removal method) utilizing the MAP formation reaction, phosphorus-containing water is passed through a reaction tower filled with MAP particles in an upward flow, and a magnesium salt is added and required. If necessary, add alkali to pH 8
Adjusted to 〜１０10, fluidized the MAP seed by air aeration,
The AP particles are brought into contact with the phosphorus component. In the conventional method of removing phosphorus by the MAP process, the molar ratio of magnesium and ammonia components to phosphorus is set to about one. In recent years, the molar ratio of magnesium ions to phosphorus (Mg ²⁺ / PO ₄ ^3- ) has been
And the molar ratio of ammonium ion to phosphorus (NH
It has been proposed that ₄ ⁺ / PO ₄ ^3- ) be 1 to 10.

[0004]

In the above-mentioned conventional dephosphorization method utilizing the MAP generation reaction, the phosphorus concentration in the treated water cannot be reduced to 7 mg / L or less.

[0005] Orthophosphorous phosphorus (PO ₄ -P) in treated water
When the concentration of is too high, it cannot be discharged as it is. For this reason, the conventional phosphorus removal method by the MAP process is used in a field such as an anaerobic digestion / desorption solution in which wastewater having a considerably high phosphorus concentration is treated and the treated water is not discharged as it is.

An object of the present invention is to provide a method for removing phosphorus by a MAP process in which the concentration of phosphorus in treated water is significantly lower than before.

[0007]

According to the method for removing phosphorus of the present invention, phosphorus-containing water is introduced into a reaction tower, and the pH is kept within a predetermined range in the presence of a magnesium salt and an ammonium salt to remove phosphorus. The removal method is characterized by coexisting a magnesium salt at a molar ratio of at least three times with respect to phosphorus and an ammonium salt at a molar ratio of at least three times with respect to phosphorus.

[0008] In the present invention, magnesium ions and ammonium ions are present in the MAP formation reaction region in the vicinity of the phosphate ions in excess of the MAP formation equivalent, thereby increasing the MAP formation rate and increasing the MAP generation rate in the treated water. MAP until phosphorus concentration is much lower than before
Is generated.

In the present invention, as the phosphorus-containing water, in addition to those containing a high concentration of phosphorus such as an anaerobic digestion / desorption solution,
Even if the phosphorus concentration is relatively low, such as food wastewater, chemical wastewater, and pharmaceutical wastewater, the phosphorus removal treatment can be sufficiently performed.

As the magnesium salt, an inorganic magnesium salt having high solubility such as magnesium chloride and magnesium sulfate is preferable, but magnesium hydroxide can also be used. (That is, in this specification, the magnesium salt includes not only a compound of an acid and a base but also magnesium hydroxide.) Since magnesium hydroxide has low solubility, magnesium hydroxide is added as a magnesium source. When ^{performing, the} molar ratio (Mg ²⁺ / P
It is preferable that the added amount of O ₄ ^3- ) be 5 times or more, especially 6 times or more.

If the addition amount of the magnesium salt is too large, the processing cost increases. Therefore, the molar ratio of magnesium to phosphorus is preferably 10 or less, particularly 8 or less.

The magnesium salt is conveniently added as an aqueous solution of a magnesium salt, but wastewater containing magnesium ions or seawater may be added. The magnesium hydroxide may be added with an acid, ammonia, ammonium hydroxide or an ammonium salt (hereinafter, these may be referred to as an ammonium source) in order to promote the dissolution. Obviously, the magnesium salt and the magnesium hydroxide may be used in combination.

As the ammonium salt, an inorganic ammonium salt having high solubility such as ammonium chloride and ammonium sulfate is preferable, but other ammonium salts may be used. In addition, in the case of ammonium hydroxide, it is preferable to add at least 5 times the molar ratio to phosphorus.

When the phosphorus-containing water to be treated contains a large amount of ammonium salts or ammonia, such as in an anaerobic digestion / desorption solution, the total amount of the ammonium source and the ammonium component in the phosphorus-containing water is reduced to the phosphorus concentration. On the other hand, the molar ratio may be three times or more. If the concentration of the ammonium salt or the like in the phosphorus-containing water is three times or more in molar ratio with respect to the phosphorus concentration, the ammonium source need not be added.

When ammonia is diffused from the water to be treated due to aeration in the reaction tower or the like, an ammonium salt is added so that the molar ratio of the ammonium component to the phosphorus concentration becomes 4 times or more, and water is added. In the case of ammonium oxide, it is preferable to add it in a molar ratio of 6 times or more.

In the present invention, as the reaction tower, an aeration combined type is used.
Various types such as a packed tower type, a fluidized bed type, a plug flow type and a complete mixing type can be used.

In the present invention, the pH of the reaction zone in the reaction tower is
The pH is preferably 8 to 9.5, particularly preferably 8 to 9.5.
Usually, an alkaline agent such as NaOH is added to the reaction tower to adjust the pH to the above range. However, when the above pH range is achieved by adding ammonium hydroxide as an ammonium source, it is necessary to add an alkaline agent such as NaOH. There is no. When the pH of the reaction zone in the reaction tower is in the above range, the pH of the treated water in the upper part of the reaction tower is also in the above range, so that the detection pH of the pH meter provided in the upper part of the reaction tower is in the above range. good.

It is preferable that seed crystals are present in the reaction tower. This seed crystal is preferably MAP particles, but may be other particles such as sand.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIG.

In the following embodiments, a magnesium salt and an ammonium salt are added to the reaction tower, but may be magnesium hydroxide or ammonium hydroxide as described above.

Reference numeral 1 denotes a reaction tower having an open top, which is connected to an inlet piping 2 for raw water (sewage, anaerobic digestion and desorbed liquid of night soil, and phosphorus-containing water such as raw night soil) equipped with a pump P ₁ at the bottom. I have. The pipe 2 is 20 cm from the lower end of the reaction tower 1.
It is preferable that the connection is made within the following range. Reaction tower 1
Has a conical shape (preferably a conical shape having an inclination angle of 60 ° or more) so that MAP particles can be easily pulled out. The lower part of the reaction tower 1 is connected with a supply pipe 4 for a magnesium salt solution, a supply pipe 5 for an alkali agent such as NaOH, and a supply pipe 8 for an ammonium salt solution.

At the bottom of the reaction tower 1, a discharge pipe 6 for MAP particles is provided.
Is connected, and a valve 6 a is provided in the discharge pipe 6.

An outlet pipe 3 for treated water is connected to the top of the reaction tower 1 via an overflow weir 11.

A circulation pipe 7 is connected to the upper part of the reaction tower 1.

[0025] Some of the treated water is withdrawn from the top of the reaction column 1 to the circulation pipe 7, the reaction tower 1 via the pump P ₂
Circulated to the bottom. 10 is an air diffuser, and 12 is a pH meter. It is preferable that the air diffuser 10 is provided above the cone-shaped portion at the lower part of the reaction tower 1.

In the reaction tower 1, p detected by the pH meter 12
An alkali agent such as NaOH is injected from the supply pipe 5 so that H is in a range where MAP is precipitated, that is, pH is 8 to 10. Further, a magnesium salt solution is injected from the pipe 4 and an ammonium salt is injected from the pipe 8 such that the magnesium salt and the ammonium salt each have a ratio of 3 mol times or more of the phosphoric acid concentration in the raw water.

In the reaction tower 1, MAP which has already been deposited
MAP is precipitated using the particles as seed crystals. That is, the MAP is caused by the inflow of the raw water, the circulation of the treated water, and the aeration from the diffuser 10.
The particles are in a fluidized state, new MAP is deposited on the surface of the MAP particles, and the MAP particles grow.

In the MAP precipitation process, if the phosphorus concentration of the raw water is excessively high, the supersaturation degree of the MAP becomes excessively high in the reaction tower 1 so that the fine crystals of the MAP self-precipitate in a liquid other than the seed crystal surface. , there is a problem that large of MAP particles can not be obtained, in this dephosphorization device, by circulating withdrawn from the reaction tower 1 treated water pipe from the upper portion of the 7 and the pump P _2, the reaction tower 1 Can reduce the phosphorus concentration in the MAP precipitation reaction section. Thereby, the degree of supersaturation of the MAP in the reaction tower 1 is reduced, and the MAP does not self-precipitate as microcrystals, but is mostly a seed crystal MA.
It precipitates only on the surface of P particles and promotes the growth of MAP particles. The circulation of the treated water is preferably performed such that the phosphorus concentration in the MAP precipitation reaction section in the reaction tower 1 becomes 100 mg / L or less, particularly 40 to 80 mg / L.

The treated water whose phosphorus concentration has decreased due to the precipitation of MAP rises in the reaction tower 1 and is discharged from the discharge pipe 3.

The MAP particles grown in the reaction tower 1 are continuously or intermittently taken out from a discharge pipe 6 below the reaction tower 1.

In the present invention, the diffuser 10 is not necessarily required, but by providing the diffuser, the liquid in the reaction tower can be efficiently stirred.

[0032]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 A synthetic wastewater prepared by dissolving monopotassium phosphate in pure water at a ratio of 30 mg / L as phosphorus in a reaction tower having a shape made of a polyvinyl chloride column having an inner diameter of 30 mm and a height of 2,000 mm as shown in FIG. At a flow rate of 250 mL / min. Also, a 0.1% aqueous solution of magnesium chloride and a 0.1% aqueous solution of ammonium chloride were continuously added so that the molar ratios of Mg: P = 3 and N: P = 3. The pH was detected by a pH meter provided at the top of the column, and the pH was adjusted by adding a NaOH solution into the column so that the detection value of the pH meter became 8.7.

The circulation pipe is connected to a point 500 mm from the top of the tower. The amount of circulating water was 250 mL / min.

As a result, the PO ₄ -P concentration in the treated water was 3.5 mg / L.

Example 2 Except that the added amounts of magnesium chloride and ammonium chloride were respectively Mg: P = 5 and N: P = 5, the solution was passed in the same manner as in Example 1, and PO ₄ − in the treated water was obtained. P
The concentration was 3.3 mg / L.

COMPARATIVE EXAMPLE 1 Except that the amounts of magnesium chloride and ammonium chloride added were respectively Mg: P = 2 and N: P = 2, the solution was passed in the same manner as in Example 1, and PO ₄ − P
The concentration was 7.1 mg / L.

Comparative Example 2 Except that the amounts of magnesium chloride and ammonium chloride added were respectively Mg: P = 2.8 and N: P = 2.8, the solution was passed in the same manner as in Example 1 to obtain treated water. P
The O ₄ -P concentration was 7.0 mg / L.

[0039] Comparative Example 3 amount of magnesium chloride and ammonium chloride, respectively Mg: P = 1, N: where except for the P = 5 and liquid permeation in the same manner as in Example 1, the treated water PO ₄ - P
The concentration was 7.2 mg / L.

COMPARATIVE EXAMPLE 4 Except that the amounts of magnesium chloride and ammonium chloride to be added were respectively Mg: P = 5 and N: P = 1, the solution was passed in the same manner as in Example 1 to obtain PO ₄ − in the treated water. P
The concentration was 7.0 mg / L.

As in Examples 1 and 2 and Comparative Examples 1 to 4, it is clear that the P concentration in the treated water is significantly reduced by setting the Mg: P and N: P ratios to 3 or more. .

[0042]

As described above in detail, according to the phosphorus removing method of the present invention, in the method of removing phosphorus in raw water as MAP particles, the phosphorus concentration in treated water can be made extremely low.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a phosphorus removing method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 reaction tower 6 MAP removal pipe 7 circulation pipe 10 diffuser pipe 11 overflow weir 12 pH meter

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masao Tsunekawa Kurita Kogyo Co., Ltd., 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo

Claims (1)

[Claims] 1. A method for removing phosphorus by introducing phosphorus-containing water into a reaction column and maintaining the pH within a predetermined range in the presence of a magnesium salt and an ammonium salt, wherein the molar ratio of the phosphorus to the phosphorus is three times. A method for removing phosphorus, comprising coexisting the above magnesium salt and an ammonium salt at a molar ratio of 3 times or more with respect to phosphorus.