JPH1157748A - Method of removing phosphorus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable effectively recovering phosphorus particles of large particle diameter in a method in which after raw water introduced from the lower part of a reactor is treated, the treated water is taken out from the upper part of the reactor and a part thereof is refluxed by stopping the circulation of the treated water when taking out reaction products from the lower part of the reactor. SOLUTION: A reactor 1 is provided with introducing piping 2 for raw water (phosphorus containing water such as sewage and raw night soil) and take-out piping 3 for treated water in the lower and the upper part thereof respectively. The bottom part of the reactor 1 is formed into a cone so that MAP particles are easily drawn out. And the reactor 1 is provided with a feeding pipe 4 for solution of magnesium salt such as MgCl2 and a feeding pipe 5 for an alkaline agent NaOH or the like, and a discharge pipe 6 for MAP(magnesium ammonium phosphate) particles in the lower part and the bottom part of thereof respectively. And treated water taken out by the take-out piping 3 is stored in a treated water tank 7 and a part thereof is circulated in the lower part of the reactor 1 by piping 8. At this time, when taking out the MAP particles from the discharge pipe 6, the circulation is stopped to make taking out them easy.

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 and recovering phosphorus in water containing phosphorus as MAP (magnesium ammonium phosphate). Particularly, it is possible to selectively separate and recover MAP particles having a large particle diameter. It relates to a method for dephosphorization.

[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, night soil, and wastewater, magnesium ion is conventionally added to phosphorus-containing water To generate MAP from ammonia and phosphorus and magnesium contained in the water, and to separate and recover the generated MAP particles.

[0003] In the conventional dephosphorization method utilizing this MAP formation reaction, phosphorus-containing water is passed through a reaction tower filled with MAP particles in an upward flow, magnesium salts are added, and alkali is added as necessary. It is adjusted to pH 8 or more by adding, and the MAP packed bed is fluidized by air aeration, and the MAP particles are stirred and mixed to form a fluidized bed.

[0004] Japanese Patent No. 2576679 discloses that in such a fluidized bed type dephosphorizer, a part of the treated water is supplied to a reaction tower in order to increase the phosphorus removal efficiency and promote the enlargement of MAP particles. It is described that a circulating means for circulating is provided at a lower portion. In addition, this patent 2576
Japanese Patent Application Laid-Open No. 679 describes that MAP particles are intermittently extracted while the circulation of the treated water is continued.

[0005] Incidentally, the MAP particles recovered by such a dephosphorization treatment are effectively used as a slow-release fertilizer. For this purpose, an organic suspended solid (SS) in a reaction tower is used.
It is desired to efficiently separate the MAP particles and recover high-quality MAP particles with high purity.

In order to improve the purity of the recovered MAP particles,
After the supply of raw water is stopped, air is blown into the reaction tower from the raw water introduction part at the bottom of the reaction tower to stir the inside of the reaction tower, and then the air blowing is stopped and allowed to stand still, thereby allowing the MAP particles and other suspended particles to float. Separation from substances has been proposed. According to this method, the MAP particles and other suspended solids are separated by a specific gravity difference during the sedimentation process by allowing the MAP particles to stand still after blowing air, so that only the MAP particles having a high specific gravity can be recovered from the bottom of the reaction tower. it can.

[0007]

In the above dephosphorization method, when recovering MAP particles, not only high-purity MAP particles but also large MAP particles in the reaction tower are selectively recovered. Is the reaction efficiency and the recovered MA
This is important in terms of the processing efficiency of P particles.

That is, when the MAP particles in the reaction tower become excessively large, the MAP particles do not flow even by air agitation or upward flow due to raw water or circulating water, and the efficiency of the MAP precipitation reaction on the surface of the MAP particles deteriorates. .

Further, the recovered MA extracted from the bottom of the reaction tower
The P particles are then dried in a drying step and then sent to a post-processing step.
Since particles have better drainage properties, effective drying can be performed.

[0010] The MAP particles withdrawn from the bottom of the reaction tower are generally collected and received by a mesh filter.
If the extracted MAP particles have a small particle size, the mesh filter is clogged.

From the above, MAP from the reaction tower
In collecting the particles, it is desired to selectively extract the MAP particles having a large particle diameter and to leave the MAP particles having a small particle diameter in the reaction tower, in addition to separating and collecting only the MAP particles. With the conventional method, it has been difficult to selectively recover large MAP particles.

That is, according to the air stirring and the subsequent standing, MAP particles and organic SS can be separated, but it is difficult to selectively separate only MAP particles having a large particle diameter.

In the dephosphorization apparatus described in Japanese Patent No. 2576679, the MAP particles having a large particle diameter tend to settle at the bottom of the reaction tower by reducing the flow LV of the circulating water, and the MAP particles having a large particle diameter Although it is possible to increase the amount of water drawn out, good selectivity cannot be obtained in this case, but rather, a problem arises in that the reaction efficiency is reduced by reducing the circulation LV of the circulating water.

The present invention solves the above-mentioned conventional problems, and in the dephosphorization method of separating raw water from flowing upward into a reaction tower and separating and recovering MAP particles from a lower part of the reaction tower, a large-diameter MAP particle is selected. It is an object of the present invention to provide a method for efficiently and efficiently collecting.

[0015]

The dephosphorization method of the present invention comprises:
Raw water is introduced from the lower part of the reaction tower, treated water is taken out from the upper part of the reaction tower, a part of the treated water is circulated to the lower part of the reaction tower, and a reaction product is taken out from the lower part of the reaction tower. In taking out an object, the circulation of the treated water is stopped.

According to the method of the present invention, the organic SS is pushed up to the upper part of the reaction tower by the upward flow of the circulating water,
The AP particles are effectively classified, and after the circulation is stopped, the smaller the MAP particles, the smaller the MAP particles are, the smaller the MAP particles are in the lower portion of the reaction tower as the MAP particles of the same specific gravity are larger. It becomes deposited on the layer. Therefore, only the MAP particles having a large particle diameter can be selectively extracted from the lower portion of the reaction tower.

In the present invention, it is preferable that aeration is performed by a diffuser provided below the reaction tower, and the treated water is circulated below the diffuser.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the dephosphorization method of the present invention, and FIG. 2 is a sectional view showing a deposited state of MAP particles according to the present invention.

In FIG. 1, reference numeral 1 denotes a reaction tower having an open top. Extraction pipe 3 is provided. The bottom of the reaction tower 1 is formed in a cone shape so that MAP particles can be easily extracted. Reaction tower 1
A supply pipe 4 for a magnesium salt solution such as MgCl ₂ (so long as it contains a magnesium salt, and may be seawater) and a supply pipe 5 for an alkali agent such as NaOH are provided at the lower part of the bottom part. Is provided with a discharge pipe 6 for MAP particles.

The treated water taken out by the take-out pipe 3 is stored in a treated water tank 7, a part of which is circulated to the lower part of the reaction tower 1 through a pipe 8, and the remainder is discharged out of the system through a pipe 9.

10 is an air diffuser, 11 is an overflow weir, 12 is pH
It is total.

P ₁ and P ₂ are pumps, and V is a valve for extracting MAP particles.

In the reaction tower 1, an alkaline agent such as NaOH is injected from the supply pipe 5 so that the pH condition at which MAP precipitates, that is, pH 7.7 to 9.0, preferably pH 8.1. When magnesium is insufficient for MAP precipitation, a magnesium salt solution such as MgCl ₂ is injected from the supply pipe 4.

In the reaction tower 1, MAP which has already been deposited
MAP is granulated using the particles as seed crystals. In other words, the inflow of raw water, the circulation of treated water, and the aeration from
The P particles are in a fluidized state, new MAP is deposited on the surface of the MAP particles, and large MAP particles are granulated.

In the precipitation of MAP, if the phosphorus concentration of raw water is high, there is a problem that MAP microcrystals are self-precipitated in the absence of seed crystals and large MAP particles cannot be obtained. in apparatus by circulating withdrawn by reaction column 1 in the treated water pipe 8 from the treating tank 7 and the pump P _2, the phosphorus concentration of MAP granulation reaction of the reaction tower 1 can be reduced. Thereby, the degree of supersaturation of the MAP in the reaction tower 1 decreases, and the MAP does not self-precipitate as fine crystals, but precipitates only on the surface of the seed MAP particles, thereby promoting the enlargement of the MAP particles. The circulation of the treated water reduces the phosphorus concentration in the MAP granulation reaction section in the reaction tower 1 to a phosphate concentration of 100 mg / L or less, particularly 40 to 80 mg.
/ L is preferable.

The treated water having a reduced phosphorus concentration due to the precipitation of MAP rises in the reaction tower 1 and is discharged from the discharge pipe 3. At this time, since the MAP particles are large, even when treating raw water containing a large amount of organic SS, MA
P particles are well separated by precipitation without being discharged together with SS. That is, since the MAP particles have a specific gravity and a particle size which are sufficiently larger than those of the organic SS, they settle and separate with good separability, and only the organic SS is contained in the treated water and the overflow weir 11
Is discharged over the

The MAP particles that have become large in the reaction tower 1 are intermittently taken out from a discharge pipe 6 below the reaction tower 1.

In the present invention, MAP is stirred by circulating water.
The particles and the organic SS are separated, and the MAP particles are also effectively classified for each particle size. Then, per the withdrawal of the MAP particles, a pump P ₂ is stopped by stopping the circulation, as shown in FIG. 2, the large particle size MAP particles (A)
The smaller the MAP particles (B) are deposited on the bottom of the reaction tower 1 and the upper portion of the large MAP particles (A), and the organic SS (C) is further deposited thereon. It becomes deposited.

In the present invention, in order to effectively separate the MAP particles from the organic SS and classify the MAP particles by the stirring effect of the circulating water, the LV in the reaction tower 1 during operation must be set at 4 ° C.
It is preferable that the treated water is circulated so as to have a flow rate of 0 to 70 m / hr, particularly 45 to 60 m / hr, and it is preferable that the MAP particles are extracted after the circulation is continued for 5 minutes or more.

In order to efficiently deposit large-diameter MAP particles on the bottom side of the reaction tower 1, the circulation is stopped, the aeration from the air diffuser 10 and the introduction of raw water are also stopped.
After the circulation, aeration and introduction of raw water are stopped, it is preferable that the MAP particles are extracted after standing for 2 to 5 minutes. However, it is not always necessary to stop the aeration and the introduction of the raw water. When the raw water is introduced above the circulating water introduction section, the introduction of the raw water may be continued.

In the present invention, a diffuser is not necessarily required, but by providing a diffuser, the liquid in the reaction tower can be efficiently stirred. The air diffuser is preferably provided in the lower part of the reaction tower in the reaction tower 1, which has an effect of increasing the effective volume of the MAP reaction granulation section.
Aeration by this air diffuser is 0.02 to 0.06 m ³ / min /
It is preferably carried out at m ³ (granulation reaction section volume). Further, it is preferable that the raw water is introduced into a position below the air diffuser, thereby producing an effect of improving the MAP reaction rate by generating an appropriate supersaturated region.

In the illustrated example, only the magnesium salt and the alkali agent are added. However, when ammonia is insufficient for the generation of MAP, it is necessary to further add ammonia to the reaction tower.

[0034]

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

Example 1 MAP particles having a particle size of 0.25 mm or more and 2.4 mm or less were put into a reaction tube having a diameter of 50 mm and a height of 2000 mm, and water extracted from the top of the reaction tube was introduced into the bottom of the reaction tube.
After stirring with circulating water at 0 m / hr for 5 minutes, the circulation was stopped. The apparent volume of the MAP particles used was 7
00 mL, and the particle size distribution and average particle size are as shown in Table 1.

After leaving the circulation for 5 minutes, the MAP particles were withdrawn from the bottom of the reaction tube by apparent volume of 100 mL.
The particle size distribution and the average particle size of the extracted MAP particles were examined by image analysis, and the results are shown in Table 1.

COMPARATIVE EXAMPLE 1 In Example 1, instead of stirring with circulating water, air was blown in from the bottom of the reaction tube at 2000 mL / min to stir the air. The particle size distribution and average particle size of the MAP particles were examined, and the results are shown in Table 1.

[0038]

[Table 1]

According to Table 1, the MAP particles can be classified more effectively and the MAP particles can be classified more effectively by the method of the present invention in which the mixture is left standing after stirring with circulating water than in the method in which the mixture is left standing after stirring with air. It can be seen that MAP particles can be selectively recovered.

[0040]

As described above in detail, according to the dephosphorization method of the present invention, in the dephosphorization method for removing and recovering phosphorus in raw water as MAP particles, the MAP particles having a large particle size and containing no organic SS. Can be selectively and efficiently separated and recovered. For this reason, since the MAP particles having a small particle size remain in the reaction tower, the fluidity of the MAP particles is good, the MAP precipitation reactivity on the particle surface is good, and the dephosphorization efficiency is improved. Moreover, since the collected MAP particles have high purity and a large particle size, they are excellent in subsequent handling properties and drainage properties, can be efficiently dried, and can be effectively used as slow-release fertilizers.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view showing a deposited state of MAP particles according to the present invention.

[Explanation of symbols]

 1 reaction tower 7 treated water tank 10 diffuser

Claims (2)

[Claims] 1. A dephosphorization method in which raw water is introduced from a lower part of a reaction tower, treated water is taken out from an upper part of the reaction tower, a part of the treated water is circulated to a lower part of the reaction tower, and a reaction product is taken out from a lower part of the reaction tower. In the method for removing phosphorus, the circulation of the treated water is stopped when removing the reaction product. 2. The dephosphorization method according to claim 1, wherein aeration is performed by a diffuser provided below the reaction tower, and the treated water is circulated to a position below the diffuser.