JP2008183562A - Dephosphorization apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dephosphorization apparatus in which raw water is made to pass through a reaction column as an upward current and MAP particles are separated and recovered from the lower part of the reaction column and dephosphorization is performed efficiently by using inexpensive magnesium hydroxide. <P>SOLUTION: Raw water is supplied to the lower part of the reaction column 1 and the treated water is withdrawn from the upper part of the reaction column 1. A part of the treated water is circulated to the lower part of the reaction column 1 and the produced MAP particles are withdrawn from the lower part of the reaction column 1. Not only NaOH but also the magnesium hydroxide slurry prepared by adding sulfuric acid of about 0.5 equivalent to magnesium hydroxide are supplied to the reaction column 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for removing phosphorus in phosphorus-containing water as MAP (magnesium ammonium phosphate), and more particularly to a dephosphorization apparatus in which magnesium hydroxide is used as a magnesium source for MAP production.

  As a method of removing phosphorus from phosphorus-containing water such as sewage, human waste, wastewater, etc., sludge dewatered filtrate generated in the aerobic treatment process, digestion and desorption liquid, magnesium ions have been added to phosphorus-containing water, A method has been proposed in which MAP is generated from the ammonia component and phosphorus and magnesium ions contained in the water, and the generated MAP particles are separated and recovered.

  In a conventional dephosphorization apparatus that uses this MAP production reaction, phosphorus-containing water is passed upward through a reaction column packed with MAP particles, and a magnesium salt (usually magnesium chloride) is added and as necessary. Then, alkali (usually NaOH) is added to adjust the pH to 8 or more, and MAP is precipitated on the MAP particles.

  As described above, in the conventional dephosphorization apparatus using the MAP process, magnesium chloride is added as a magnesium ion source. However, this magnesium chloride is more expensive than magnesium hydroxide, and inexpensive magnesium hydroxide is used. Is expected. However, the solubility of magnesium hydroxide in water is considerably lower than that of magnesium chloride, and only about several ppm of magnesium ions are present in the water of the magnesium hydroxide slurry (pH about 10.5). In particular, the dissolution rate of magnesium hydroxide in alkaline water of pH 8-9 where the MAP precipitation reaction proceeds is considerably low. For this reason, the dissolution rate of magnesium hydroxide becomes rate-limiting in the MAP precipitation reaction, and the treatment time for removing phosphorus becomes extremely long.

  An object of the present invention is to solve such problems and to provide a dephosphorization apparatus capable of efficiently generating MAP particles using inexpensive magnesium hydroxide.

請 dephosphorization device Motomeko one aspect of the present invention, the phosphorus-containing water is introduced into the lower reaction tower, the dephosphorization device taken out from the reaction tower top the treated water, a mixture of magnesium hydroxide and ammonium ion-containing water phosphorus Means for adding to the contained water is provided.

Thus, when the ammonium ions coexist in the water, dissolution is promoted to water of magnesium hydroxide, MAP precipitation reaction is faster.

In dephosphorization device according to claim 1 for promoting the dissolution of the magnesium hydroxide by A Nmo ion _{^{is, [Mg 2+ / PO 4 -P}} ] (molar ratio) 1-3, in particular at 1.2 to 2.5 It is preferred to add magnesium hydroxide . Relationship ammonium ions and magnesium hydroxide _{^{[Mg 2+ / NH 4 -N]}} ( molar ratio) is 0.75 or less, especially 0.5 or less conditions are preferred.

Examples of such ammonium ion-containing water include sludge dry gas treatment wastewater (NH ₄ —N concentration of about 300 ppm), ammonia stripping absorbent (NH ₄ —N concentration of about 20000 ppm), ion exchange resin, and the like. Examples include reclaimed waste liquid (NH ₄ —N concentration 2000 ppm). Magnesium hydroxide is added to this ammonium ion-containing water to promote dissolution of magnesium hydroxide, and then this magnesium hydroxide dispersion water (partially dissolved water of magnesium hydroxide) is introduced into the reaction tower or treated Mix in raw water.

  In the present invention, the phosphorus-containing water includes, for example, electric dust collection wastewater (phosphorus concentration of about 70 to 80 ppm) at the time of melting sludge, sewage or human waste, sewage dehydrated filtrate, digestion desorption liquid, etc. generated in processing steps such as sewage or human waste. Illustrated.

  According to the dephosphorization apparatus of the present invention, in a dephosphorization apparatus that removes and collects phosphorus in raw water as MAP particles, dephosphorization can be efficiently performed using inexpensive magnesium hydroxide.

Reference examples and embodiments of the present invention will be described below in detail with reference to the drawings.

Figure 1 is a schematic sectional view showing a dephosphorization device according to a reference example.

An inlet pipe 2 for raw water (sewage, anaerobic digestion and desorption liquid for human waste, raw urine, etc.) having a pump P ₁ is connected to the lower part of the reaction tower 1, and treated water is connected to the upper part of the reaction tower 1. An extraction pipe 3 is connected. 11 is an overflow weir and 12 is a pH meter. Note that the top of the reaction tower 1 is open.

  The lower part of the reaction tower 1 has a cone shape so that the MAP particles can be easily extracted. In the lower part of the reaction tower 1, a supply pipe 4 of magnesium hydroxide slurry (magnesium hydroxide slurry in which magnesium hydroxide is partially dissolved by adding a smaller amount of acid than the equivalent amount to magnesium hydroxide in the mixing tank 4A). A supply pipe 5 for an alkaline agent such as NaOH is connected, and a discharge pipe 6 for MAP particles is provided at the bottom. 6a indicates a valve.

  A diffuser tube 10 is provided in the lower part of the reaction tower 1. In addition, you may make it abbreviate | omit this air diffuser 10 and to expand | deploy MAP particle | grains by a rising water flow.

Pipe 7 as a part of the water to overflow weir 11 and the overflow is recycled to the bottom, a pump P ₂ and pipe 8 are provided.

  The extraction of water into the pipe 7 is not limited to the overflow weir 11 but may be the extraction pipe 3 or the upper part of the reaction tower 1 within about 1 m from the liquid level in the reaction tower 1.

  When installing the diffuser tube 10, it is preferable to arrange it 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, and 8 are preferably connected to a height within 20 cm from the lower end of the reaction tower 1.

  Hereinafter, the operation of the dephosphorization apparatus will be described.

  Raw water is introduced into the lower part of the reaction tower 1 from the pipe 2. In the reaction tower 1, an alkaline agent such as NaOH is injected from the supply pipe 5 so that the pH condition for precipitation of MAP, that is, the pH is about 8-10. A magnesium hydroxide slurry is injected from the supply pipe 4.

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

In this MAP precipitation process, if the phosphorus concentration of the raw water is excessively high, MAP microcrystals are self-precipitated in a liquid other than the seed crystal surface, and MAP particles are difficult to grow. In the phosphorus device, the phosphorus concentration in the MAP precipitation reaction part in the reaction tower 1 can be lowered by circulating the treated water of the reaction tower 1 by the pipes 7 and 8 and the pump P ₂ .

  As a result, the supersaturation degree of MAP in the reaction tower 1 is lowered, and MAP is not precipitated as microcrystals, but mostly precipitates on the surface of seed MAP particles and promotes the growth of MAP particles. The treatment water is preferably circulated so that the phosphorus concentration in the reaction section in the reaction tower 1 is a phosphate concentration of 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 is discharged from the extraction pipe 3.

  When the amount of MAP particles in the reaction tower 1 exceeds a predetermined value, it is taken out intermittently or continuously from the discharge pipe 6 below the reaction tower 1.

  In the illustrated example, only the magnesium hydroxide slurry and the alkali agent are added. However, when the ammonia component is insufficient for the production of MAP, ammonia or ammonium salt is further added to the reaction tower.

Although the magnesium hydroxide slurry is added to the reaction tower 1 in FIG. 1, the magnesium hydroxide slurry may be added to the raw water supply pipe 2. For example, an acid may be added to the Mg (OH) ₂ slurry, and this mixed solution may be added to the raw water supply pipe 2. Further, the Mg (OH) ₂ slurry and the acid can be separately added to the raw water supply pipe 2. In this case, the order of adding the Mg (OH) ₂ slurry and the acid to the raw water supply pipe 2 may be first, or both may be added to the raw water at the same time.

Figure 2 is a schematic cross-sectional view of dephosphorization device according to an embodiment of the invention of claim 1.

In this embodiment, magnesium hydroxide and wastewater with high ammonium ion concentration (high NH ₄ ⁺ drainage) are supplied to the mixing tank 4B. As described above, ammonium ions have an action of promoting the dissolution of magnesium hydroxide, and a magnesium hydroxide slurry-containing liquid in which a part of magnesium hydroxide is dissolved by this high NH ₄ ⁺ drainage is supplied to the reaction tower via the supply pipe 4. 1 is supplied.

  Other configurations of the embodiment of FIG. 2 are the same as those of FIG. 1, and the same reference numerals denote the same parts.

Although the magnesium hydroxide slurry is directly supplied to the reaction tower 1 in FIG. 2, the magnesium hydroxide slurry may be added to the raw water supply pipe 2. Further, the magnesium hydroxide slurry and the high NH ₄ ⁺ drainage may be separately added to the raw water supply pipe 2.

FIG. 3 is a schematic cross-sectional view of a dephosphorization apparatus according to a reference example . In this embodiment, magnesium hydroxide is added to phosphorus-containing wastewater having a high ammonium ion concentration, and the liquid after this addition is introduced into the reaction tower 1.

The present invention will be described more specifically with reference to the following reference examples, examples and comparative examples.

Reference example 1
The dimensions and the like of each member of the apparatus shown in FIG. 1 (however, a diffuser tube is not installed) are as follows.

Reaction tower 1
Reaction part height 1500mm, diameter 50mm,
Cone-shaped part 43mm in height
Separation part height 150mm, diameter 70mm
The water flow conditions were as follows.

Raw water: 1 potassium phosphate and ammonium chloride dissolved in water to the following concentrations.

PO ₄ -P 150ppm
NH ₄ —N 600 ppm
pH 7.3
Raw water supply amount: 35.7 L / Hr (average residence time in reaction section of raw water reaction tower: 5 minutes)
Circulation flow rate: 82L / Hr
Upflow LV of reaction section: 60 m / Hr
Magnesium agent: sulfuric acid in the mixing tank 4A for 1 wt% slurry of Mg (OH) ₂
Liquid (slurry) in which 0.5 equivalent of Mg (OH) ₂ was added. This
To raw water PO ₄ -P concentration Larry, the molar ratio of Mg / P is ne 1.5
NaOH addition amount: 1% solution added, so that overflow pH becomes 8.0 Initial seed crystal: MAP 1500 g of 0.5-1 mm
Table 1 shows the results of measuring the concentration of PO ₄ -P in the treated water after continuously passing water for 3 days under the above conditions.

Comparative Example 1
Reference Example 1 except that magnesium hydroxide and sulfuric acid were not used and a 1% aqueous solution of MgCl ₂ was supplied from the supply pipe 4 to the reaction tower 1 so that Mg / P (molar ratio) = 1.5. Using the same dephosphorization apparatus, this dephosphorization apparatus was operated under the same conditions, and the concentration of PO ₄ -P in the treated water was measured. The results are shown in Table 1.

Comparative Example 2
In Reference Example 1, the addition of sulfuric acid to the mixing tank 4A was stopped. The raw water flow rate and the circulating water amount were as shown in Table 1, and the average residence time in the reaction part of the raw water was 30 minutes. The amount of Mg (OH) ₂ added was increased as shown in Table 1.

Otherwise, the dephosphorization apparatus was operated in the same manner as in Reference Example 1, and the PO ₄ -P concentration in the treated water was measured. The results are shown in Table 1.

As is apparent from Table 1, according to Reference Example 1, phosphorus removal equivalent to that in Comparative Example 1 using MgCl ₂ can be performed. Comparative Example 2 using only Mg (OH) ₂ is inferior in phosphorus removal performance compared to these.

Example 1
The dimensions and the like of each member of the apparatus shown in FIG. 2 (however, a diffuser tube is not installed) are as follows.

Reaction tower 1
Reaction part height 2000mm, diameter 30mm,
Cone-shaped part 43mm in height
Separation part height 150mm, diameter 70mm
The water flow conditions were as follows.

Raw water: 1 potassium phosphate and ammonium chloride dissolved in water to the following concentrations.

PO ₄ -P 200ppm
pH 6.8
Raw water supply amount: 14.4 L / Hr (average residence time in reaction section of raw water reaction tower: 6 minutes)
Circulation flow rate: 13.6 L / Hr
Upflow LV of reaction section: 60 m / Hr
Magnesium agent: 0.19 wt% ammonium chloride aqueous solution (NH ₄ —N concentration: 50
Proportion of Mg (OH) ₂ of 1 wt% at 0 mg / L) relative to the mixing tank 4B
(Slurry) added in Average residence time in mixing tank 4B is 5 minutes 3
0 seconds. This slurry was mixed with Mg / P against the raw water PO ₄ -P concentration.
Added at 1.1 L / Hr so that the molar ratio is 2 NaOH addition amount: 1% solution was added so that the overflow pH was 8.0 The initial seed crystals were the same as in Reference Example 1. Table 2 shows the results of measuring the concentration of PO ₄ -P in the treated water by continuously passing water for 3 days under the above conditions.

Comparative Example 3
No magnesium hydroxide was added to the mixing tank 4B, and the same magnesium chloride 2 wt% aqueous solution as in Example 1 was supplied from the pipe 4 at 0.9 L / Hr. As a Mg source for generating MAP, a 1% aqueous solution of MgCl ₂ was supplied so that Mg / P (molar ratio) = 2. Other than this, the same dephosphorization apparatus as in Example 1 was used, and this dephosphorization apparatus was operated under the same conditions, and the PO ₄ -P concentration in the treated water was measured. The results are shown in Table 2.

Comparative Example 4
In Comparative Example 3, no magnesium chloride aqueous solution was added. Instead, 1 wt% slurry of Mg (OH) ₂ as an Mg source was supplied to the lower part of the reaction tower 1 so that Mg / P = 2. Further, the supply of NaOH from the supply pipe 5 was stopped.

Otherwise, the dephosphorization apparatus was operated in the same manner as in Example 1, and the PO ₄ -P concentration in the treated water was measured. The results are shown in Table 2.

As is apparent from Table 2, according to Example 1 , phosphorus removal equivalent to that of Comparative Example 3 using MgCl ₂ can be performed. Comparative Example 4 using only Mg (OH) ₂ is inferior in phosphorus removal performance compared to these.

It is sectional drawing which shows the dephosphorization apparatus which concerns on a reference example . It is sectional drawing which shows the dephosphorization apparatus which concerns on embodiment of this invention. It is sectional drawing which shows the dephosphorization apparatus which concerns on a reference example .

Explanation of symbols

1 Reaction tower 7, 8 Circulation pipe 10 Aeration pipe

Claims (3)

  In the dephosphorization apparatus for introducing phosphorus-containing water into the lower part of the reaction tower and taking out treated water from the upper part of the reaction tower, it is provided with means for adding magnesium hydroxide and means for adding acid to magnesium hydroxide Dephosphorization device. In a dephosphorization apparatus that introduces phosphorus-containing water into the lower part of the reaction tower and removes treated water from the upper part of the reaction tower
A dephosphorization apparatus comprising means for mixing magnesium hydroxide and ammonium ion-containing water and adding the mixture to phosphorus-containing water.   A dephosphorization apparatus for introducing raw water containing phosphorus and ammonium ions into the lower part of the reaction tower and taking out treated water from the upper part of the reaction tower, comprising a means for adding magnesium hydroxide to the raw water. Phosphorus equipment.

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