JPH11267663A - Dephosphorizing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently recover magnesium ammonium phosphate(MAP) particles with large particle sizes, in a dephosphorizing device in which raw water is upward passed through a reaction tower, and the MAP particles are separated and recovered from the bottom of the reaction tower. SOLUTION: The raw water is fed to the bottom of the reaction tower 1, treated water is taken out from the upper part of the reaction tower 1 and also one portion of the treated water is circulated to the bottom of the reaction tower 1 and produced MAP particles are taken out from the bottom of the reaction tower 1. Granulating plates 20, 21 are provided on the upper part of the reaction tower 1. The granulating plates 20, 21 have a cone shape and a large number of holes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for removing and recovering phosphorus in water containing phosphorus as MAP (magnesium ammonium phosphate). Fine M
The present invention relates to a dephosphorization device capable of preventing the loss of AP particles.

[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 a conventional dephosphorizer utilizing this MAP generation 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] The MAP may be deposited from a MAP-free solution (primary nucleation) or may be deposited on the surface of an existing MAP. The former has a fine MAP particle size, usually 20 μm or less. The latter increases the MAP particle size. In some cases, the deposited MAP acts as a binder to aggregate a plurality of MAP particles, but the deposited MAP can act as a binder only when particles having a small particle size (several tens of μm or less) are used. However, when the particle size increases, the MAP particles cannot aggregate due to the shearing force accompanying the flow. It has also been confirmed that when the number of MAP particles in the reaction section increases, aggregation becomes difficult. In the reaction section, it can be considered that these phenomena are performed stochastically.

[0005]

The conventional dephosphorization method apparatus has the following disadvantages.

In the conventional dephosphorization apparatus, when the number of particles at the time of startup is small, the above-mentioned precipitated MAP tends to cause agglomeration of the particles, and the MAP particles are 200 μm in a relatively short time (about one day). However, since it is deposited on the MAP surface, the increase in the MAP particle size is slow and grows to about 1 to 2 mm.
It takes about one month. If MAP having a small particle size increases in the reaction zone for some reason, these particles hardly aggregate, and the increase in particle size becomes extremely slow. Spills over, reducing the recovery rate. The generated MAP is pulled out from the lower part of the apparatus. At this time, since the particles having a small particle size move toward the filtrate at the time of draining, the recovery rate of the MAP decreases.

In the conventional apparatus, it is important to keep the number of MAP particles in the reaction section in an appropriate range. However, once the number of particles becomes excessively large or small, MAP particles having a small particle diameter are interposed in the middle of the reaction section. The only way to do this is to pull out the MAP particles, or pull out the entire MAP particles and start over.

[0008] It is an object of the present invention to solve such problems and to provide a dephosphorizer capable of efficiently producing large-diameter MAP particles.

[0009]

The dephosphorization apparatus of the present invention comprises:
In a dephosphorizer for introducing raw water from the lower part of the reaction tower and removing treated water from the upper part of the reaction tower, a granulating plate is provided inside the reaction tower.

In the dephosphorization apparatus of the present invention, the small MAP particles rising in the liquid together with the bubbles roll on the granulating plate and aggregate. That is, as described above, MAP particles having a size of about 20 μm or more do not agglomerate due to the binder effect at the time of MAP precipitation. However, when the particles roll, they are entangled with other particles and physically aggregate. In addition, by aggregating the small MAP particles in this way, the number of particles in the reaction section can be made appropriate. Thereby, the dephosphorization device can be operated stably.

[0011] Further, the bubble colliding with the granulation plate has a lower rising speed there. At this time, the MAP particles entrained in the lower part of the bubbles are separated from the bubbles, and the MAP particles having a particle size equal to or larger than a predetermined value.
The particles settle. As a result, the amount of overflowing MAP particles decreases. For this reason, it may not be necessary to increase the cross-sectional area of the separation part in the upper part of the reaction part.

[0012]

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

FIG. 1 is a sectional view showing a dephosphorizing apparatus according to an embodiment of the present invention, FIG. 2 is a side view of a granulating plate, and FIG. 3 is a longitudinal sectional view of the granulating plate.

An inlet pipe 2 for raw water (sewage, anaerobic digestion and desorbed liquid of human waste, phosphorus-containing water such as raw human waste) having a pump P ₁ is connected to a lower part of the reaction tower 1, A pipe 3 for taking out treated water is connected. 11 is an overflow weir and 12 is a pH meter. The top of the reaction tower 1 is open.

The lower portion of the reaction tower 1 is formed in a cone shape so that MAP particles can be easily extracted. In the lower part of the reaction tower 1, M
A supply pipe 4 for a magnesium salt solution such as gCl ₂ (so long as it contains a magnesium salt, and may be seawater) and a supply pipe 5 for an alkaline agent such as NaOH are connected, and MAP particles are provided at the bottom. Discharge pipe 6 is provided.
6a shows a valve.

A diffuser 10 is provided at a lower part in the reaction tower 1, and granulating plates 20 and 21 are provided at an upper part. A pipe 7 and a pump P _{2 are provided} so that a part of water is taken out of the reaction tower above the granulation plates 20 and 21 and circulated to the bottom of the tower.
And a pipe 8.

Each of the granulating plates 20 and 21 has a cone shape, and has a large number of holes 23. The head of the upper granulation plate 20 faces downward, and the lower granulation plate 2
Numeral 1 is arranged such that the pointed head faces upward. The head of the upper granulation plate 20 has a truncated shape and an opening 24 is provided.

The granulating plates 20 and 21 are connected by a connecting member 22 such as a telescopic rod. The upper granulation plate 20 is provided with a flange 25. The flange 25 is connected to a granulation plate support bracket (not shown) provided on the inner peripheral surface of the reaction tower 1.

The angle of the inclined surfaces of the granulating plates 20 and 21 is preferably about 60 ° or more (particularly 60 to 70 °) with respect to the horizontal. The diameter of the hole 23 is 10 mm or less (especially 5 to 10
mm) is preferable, and the aperture ratio is 10% or less (especially 5%).
-10%) is preferred. The diameter of the opening 24 is preferably 30 mm or less (particularly, 20 to 30 mm). The diameter of the connecting member 22 is preferably 10 mm or less. The distance between the lower end of the granulating plate 20 and the upper end of the granulating plate 21 is preferably about 10 to 20 mm.

The outlet of water into the pipe 7 is preferably set within 1 m (particularly 50 to 100 cm) from the liquid level in the reaction tower 1. It is preferable that the level difference between the upper end of the granulating plate 20 and the outlet is 30 cm or more.

The air diffuser 10 is preferably disposed within 10 cm above the boundary between the cylindrical part and the cone part in the lower part of the reaction tower 1. The pipes 2, 4, 5, 8 are preferably connected at a height within 20 cm from the lower end of the reaction tower 1.

The operation of the dephosphorizer will be described below. Note that the range from the liquid level to the outlet for water to the pipe 7 is called a separation unit, the range from that to the diffuser 10 is called a reaction unit, and the area below it is sometimes called a storage unit.

In the reaction tower 1, an alkaline agent such as NaOH is injected from the supply pipe 5 so that the pH condition for MAP precipitation, 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 enter a fluidized state, new MAP precipitates on the surface of the MAP particles, and the MAP particles grow.

Although small MAP particles rise with the rise of bubbles, the small MAP particles are tumbled and granulated at the granulation plate portion by the provision of the granulation plates 20 and 21 to increase the diameter. I do. That is, the plate surfaces of the granulation plates 20 and 21 receive an upward force due to the upward flow. Also, near the granulation plate,
It is a turbulent state due to rising liquid and bubbles. The MAP particles that have risen together with the bubbles tend to separate from the bubbles by decelerating when the bubbles hit the granulation plates 20 and 21 or pass through the holes 23, and try to settle. At this time, the MAP particles settle down along the lower surfaces of the granulation plates 20 and 21 under the influence of the upward flow. At this time, the MAP particles collide with each other, aggregate and grow.

The plate surfaces of the granulating plates 20 and 21 receive an upward force due to the upward flow. The vicinity of the granulation plate is in a turbulent state due to the rise of liquid and bubbles. For this reason, the members supporting the granulating plates 20 and 21 and the connecting members 2
If 2 has elasticity or vibration, the granulating plates 20 and 21 vibrate finely due to upward flow in the tower, collision of bubbles, or the like. Small M along the granulating plates 20 and 21 vibrating in this manner.
When the AP particles move, the stationary granulating plate 20,
The frequency of collision between the small MAP particles is increased as compared with the case where the particles are settled along 21, and the growth of the MAP particles is promoted.

In the MAP precipitation process, when 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. phosphorus apparatus, the treated water and the reaction column 1 by circulating through a pipe 7, 8 and the pump P _2, it is possible to lower the phosphorus concentration in the reaction part of the reaction tower 1.

As a result, the degree of supersaturation of the MAP in the reaction tower 1 is reduced, 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 is carried out by the reaction tower 1
The reaction is preferably carried out so that the concentration of phosphorus in the reaction section becomes 100 mg / L or less, particularly 40 to 80 mg / L.

Further, by this circulation, the fine MAP particles are also circulated, and their overflow is prevented.

The treated water whose phosphorus concentration has decreased due to the precipitation of MAP rises in the reaction tower 1, overflows the overflow weir 11, and is discharged from the discharge pipe 3.

The MAP particles grown in the reaction tower 1
A fluidized bed is formed inside. When the amount of the MAP particles becomes equal to or more than a predetermined value, the MAP particles are intermittently taken out from the discharge pipe 6 at the lower part of the reaction tower 1. Preferably, the MAP particles are withdrawn from the discharge pipe 6 when the distance between the flow interface of the MAP particles in the reaction tower 1 and the lower end of the granulation plate 21 is within 1 m.

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

[0033]

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

Example 1 The dimensions and the like of each member of the apparatus shown in FIG. 1 were as follows.

Reaction tower 1 Reaction section height 2400 mm, diameter 150 mm Separation section height 500 mm, maximum diameter 300 mm Granulating plates 20, 21 Level difference between upper end of granulating plate 20 and circulating water outlet 300 mm Granulating plate 20 Maximum diameter of 21 120mm Angle of slope to horizontal 60 ° Diameter of hole 23 10mm Opening ratio of hole 23 10% Diameter of opening 24 30mm Distance between lower end of granulating plate 20 and upper end of granulating plate 20 20mm It was as follows.

Raw water: A solution obtained by dissolving potassium dihydrogen phosphate and ammonium chloride in pure water so as to have the following concentrations.

PO ₄ -P 100 ppm NH ₄ -N 1000 ppm pH 7.3 Raw water supply: 180 L / Hr (superficial velocity 10 m / Hr) Circulating flow rate: 30 m / Hr in terms of superficial superficial velocity 0.4 Nm ³ / Hr MgCl ₂ added amount: 1% solution was added to make a molar ratio of 1.2 with respect to the raw water PO ₄ -P concentration. NaOH added amount: 1% solution, and the overflow solution pH was 8 Temperature: 20 ° C Water is passed under the above conditions, and PO ₄ -P and TP in the treated water are added.
The concentration of (total phosphorus) was measured. Two weeks later, the MAP particles were withdrawn from the pipe 6 at the bottom of the reaction tower 1, and the particle size distribution was measured. FIG. 4 shows the measurement results.

Comparative Example 1 Using the same dephosphorizer as in Example 1 except that the granulating plates 20 and 21 were not provided, the dephosphorizer was operated under the same conditions, and PO ₄ -P, T -P and MA pulled out
The particle size distribution results of the P particles were measured and are shown in FIG.

[Discussion] As shown in FIGS. 4A and 4B, PO ₄ -P was _{4 to 5} ppm in both Example 1 and Comparative Example 1.
About the same degree. However, while TP was as low as 6 to 8 ppm in Example 1, it was 12 to 15 ppm in Comparative Example 1.
It is considerably high at ppm. Since the value obtained by subtracting the PO ₄ -P value from the TP value corresponds to the amount of the overflowed MAP particles, the amount of the overflowed MAP particles is 2 to 3 ppm in Example 1 and 8 to 10 ppm in Comparative Example 1. There is a significant difference between That is, the granulating plates 20 and 21
In Example 1, where the MAP particles were provided, the overflow of the MAP particles was extremely small.

Further, since the value obtained by subtracting the TP value in the treated water from the PO ₄ -P value in the raw water is the amount of MAP particles remaining in the reaction tower 1, Example 1 is more reactive than Comparative Example 1. It is clear that the amount of MAP particles produced in the column is much higher.

As seen in FIGS. 4C and 4D,
In Example 1, the size of the generated MAP particles was significantly larger than that in Comparative Example 1, and it is clear that the granulating effect of the granulated plate was remarkable.

[0042]

As described in detail above, according to the dephosphorization apparatus of the present invention, large-diameter MAP particles can be formed in a dephosphorization apparatus for removing and recovering phosphorus in raw water as MAP particles.

According to the present invention, the following effects are further obtained.

In a conventional apparatus, a MAP having a small particle size is used.
In many cases, the number of particles increased, the flow interface became unclear, and it was difficult to determine the MAP particle extraction. However, in the present apparatus, a stable flow interface was formed and MAP extraction was performed.
Can be operated from the flow interface height.

In the conventional apparatus, when the particles having a small particle size are excessively generated, the increase in the particle size of the MAP particles becomes extremely slow and several hundred pp while the operation is continued until the particle size increases.
When the MAP particles overflowed or were drawn out from the bottom, a considerable amount of MAP having a small particle size was mixed in, and the MAP particles flowed out to the filtrate side at the stage of draining, and the recovery rate was reduced. It was difficult to recover from the situation while driving. Even in such a state, when a granulating plate is inserted as in the present invention, it takes several days, but aggregation of small particles occurs, and a function of steadily recovering is shown.

The MAP recovery is sufficiently higher in the case of the apparatus of the present invention than in the conventional apparatus even when compared at the stage before drainage taken out of the reaction tower. However, in the present invention, the MAP particle diameter is large, and the fine MAP at the time of drainage is fine. Because there is little outflow of particles,
The MAP recovery after draining is significantly higher than in the conventional example.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a dephosphorization apparatus according to an embodiment of the present invention.

FIG. 2 is a side view of a granulation plate.

FIG. 3 is a sectional view of a granulation plate.

FIG. 4 is a graph showing measurement results of Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tower 7, 8 Circulation piping 10 Aerator tube 20, 21 Granulating plate 22 Connecting member 23 hole

Claims (1)

[Claims] 1. A dephosphorization device for introducing raw water from a lower portion of a reaction tower and removing treated water from an upper portion of the reaction tower, wherein a granulating plate is provided inside the reaction tower.