JP2000334474A - Method for removing phosphorus from waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover MAP and to obtain treated water having high water quality by efficiently removing phosphorus from a waste liquid such as a separated dehydrated liquid from a sludge wherein phosphate ions, ammoniacal nitrogen and calcium ions coexist by utilizing the MAP method (magnesium ammonium phosphate) and the HA(hydroxyapatite) crystallizing method. SOLUTION: Waste water containing phosphate ions, ammoniacal nitrogen and calcium ions is passed upwardly through a reaction tower 1 and MAP is formed as an insoluble substance from the phosphorus ions in this waste water and separated in the presence of a magnesium compound. A mixed fluidized bed of MAP and HA particles are formed in this reaction tower 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dephosphorizing wastewater, and more particularly, to a method for removing magnesium ammonium phosphate (hereinafter referred to as "water") from wastewater in which phosphate ions, ammoniacal nitrogen and calcium ions coexist, such as sludge dewatered separation liquid. "MAP"
Abbreviated. ) Method and hydroxyapatite (H
A ". A) a method for efficiently removing and recovering phosphorus by utilizing a crystallographic method;

[0002]

2. Description of the Related Art Organic sludge such as sewage sludge is concentrated and dewatered if necessary, and the resulting dewatered cake is reused or dumped after being melted or incinerated.

[0003] Concentrated separation liquid and dehydration filtrate obtained by such concentration and dehydration treatment of organic sludge (hereinafter collectively referred to as "dehydration separation liquid") are phosphate ions, ammonia nitrogen, calcium, and the like. It contains ions etc.,
This dehydrated separation liquid is processed by returning it to the biological treatment step in the preceding stage.

[0004] As a method for removing phosphorus from phosphorus-containing water, a magnesium compound is added to phosphorus-containing water, and the following reaction is carried out to remove M from ammonia nitrogen and phosphate ions and magnesium ions contained in the wastewater.
A method of generating an AP and separating and collecting the generated MAP particles has been proposed. The water to be treated by the MAP method is an anaerobic digestion and desorption solution (Japanese Patent Publication No. Hei 7-77640), an activated alumina desorption solution (Japanese Patent Application Laid-Open No. 9-85263), and the like. To be added
As described in Japanese Patent Application Laid-Open No. 8-45320, the concentration of PO ₄ -P is high-concentration phosphorus-containing water of 100 mg / L or more. Such a phosphorus removal method by the MAP method has the advantage that no excess sludge is discharged, and that phosphorus can be removed and recovered as MAP, and can be effectively reused.

MAP method: Mg ²⁺ + NH ₄ ⁺ + HPO ₄ ²⁻ + OH ⁻ + 6H ₂ O → MgN
H ₄ PO ₄ .6H ₂ O + H ₂ O On the other hand, there is an HA crystallization method in which HA is precipitated by the following reaction as a phosphorus removal method by a crystallization method. According to this method, the PO ₄ -P concentration of treated water is reduced. It can be reduced to 1 mg / L or less.

[0006] HA _{^{Akiraoriho: 5Ca 2+ + 3HPO 4 2+ 4OH}} - → Ca 5 (OH) (PO 4)
₃ + 3H ₂ O In both the MAP method and the HA crystallization method, the insolubilization reaction proceeds under weak alkaline conditions.

[0007]

As described above, phosphorus removal by the MAP method is advantageous in terms of eliminating excess sludge and recovering and reusing valuable resources, but has a sufficient phosphorus removal rate. However, there is a problem that treated water of good quality cannot be obtained. For example, when an anaerobic digestion / desorption solution having a PO ₄ -P concentration of about 100 mg / L is treated, the phosphorus removal rate is about 80%, and the PO ₄ -P concentration of the treated water is 2%.
In the case of treating low-concentration phosphorus-containing water having a lower PO ₄ -P concentration, the phosphorus removal rate is lower than about 0 mg / L.

In the phosphorus removal by the MAP method, the amount of the magnesium compound added is increased, the pH adjusted by the alkali is increased, and the Mg ²⁺ concentration and OH ⁻ concentration in the system are increased to promote the generation of MAP, PO ₄ -P of water
It is possible to reduce the concentration, but in this case,
The cost of adding the magnesium compound and the alkali increases, which is economically disadvantageous. Moreover, high pH of pH 9 or higher
In this case, the reaction for producing magnesium phosphate proceeds, which may hinder the reaction for producing MAP.

As described above, the sludge dewatered separation liquid obtained in the organic sludge concentration and dewatering step contains phosphorus, but has a PO ₄ -P concentration of about 25 to 50 mg / L, which is generally about 25 to 50 mg / L. Since it is very low as compared with an anaerobic digestion / desorption solution or the like that has been treated by the MAP method, it is difficult to efficiently remove phosphorus by the MAP method. Further, when a dehydrated separation solution containing calcium ions together with phosphate ions is treated by the MAP method, there is a problem in that calcium scale is generated in a reaction tower, a pipe, or the like, causing scale obstacles such as flow path blockage.

[0010] From the above, conventionally, the sludge dewatered and separated liquid is subjected to removal of phosphorus by the MAP method,
Although not recovered, the phosphorus contained in this dehydrated separation liquid was also removed from the viewpoint of recovery and reuse of valuables.
It is desired to remove and recover as P.

On the other hand, according to the HA crystallization method, it is possible to obtain treated water of good water quality with a PO ₄ -P concentration of 1 mg / L or less. It is considered that extremely efficient phosphorus removal can be performed by simultaneously proceeding the phosphorus removal reaction by the MAP method and the HA crystallization method in the same system in the case of wastewater in which neutral nitrogen and calcium ions coexist.

However, the presence of magnesium ions in the HA crystallization reaction system inhibits the formation of calcium phosphate salts, which impairs the formation of HA crystals or precipitates calcium phosphate salts as fine particles. However, there is also a problem that the water flows out together with the treated water to deteriorate the quality of the treated water.

The present invention has been made in view of the above-mentioned conventional circumstances, and utilizes a MAP method and an HA crystallization method to remove phosphate ions, ammonia nitrogen, calcium, etc., such as sludge dewatered and separated liquids. An object of the present invention is to provide a method for removing phosphorus from wastewater in which high-quality treated water is obtained while efficiently removing phosphorus from wastewater in which ions coexist to recover MAP.

[0014]

According to the method for dephosphorizing wastewater of the present invention, wastewater containing phosphate ions, ammoniacal nitrogen and calcium ions is allowed to flow through a reaction tower in an upward flow while the presence of a magnesium compound. Below, in a method of dephosphorizing wastewater, in which phosphate ions in the wastewater are generated as insoluble MAP from the wastewater and separated from the wastewater, a fluidized bed (a fluidized bed) of MAP particles and HA particles is provided in the reaction tower. Is formed.

When MAP particles and HA particles coexist in the reaction tower, a fluidized bed (fluidized bed) is formed,
The generation of insolubles by the AP method and the HA crystallization method can be simultaneously advanced to efficiently remove phosphorus and to recover phosphorus in wastewater as MAP.

That is, as described above, the HA crystallization reaction is inhibited by magnesium ions, but if phosphate ions and calcium ions are present at several tens of mg / L each, it is possible to generate HA, and the HA particles can be dispersed. By coexisting,
With the HA particles as nuclei, the precipitation of HA can proceed smoothly.

Precipitation of HA in this way prevents scale disturbance due to calcium scale, and also prevents the formation of fine particles of calcium phosphate and the deterioration of the quality of treated water due to the outflow of these fine particles into treated water. _4- P concentration is remarkably reduced, and treated water of good water quality with less SS can be obtained.

[0018]

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

FIG. 1 is a system diagram showing an embodiment of a reaction tower used in the waste water dephosphorization method of the present invention.

In FIG. 1, reference numeral 1 denotes a reaction tower, which is a raw water (PO ₄ − such as a sludge dewatered / separated liquid) having a pump P ₁ at its lower part.
An inlet pipe 2 for P, NH ₄ —N, and Ca-containing wastewater) is connected, and an outlet pipe 3 for treated water is connected above the reaction tower 1. Also, circulation pipe 4 is provided with a pump P ₂ for circulating a portion of the treated water to the bottom. The top of the reaction tower 1 is open, and a support plate 10 of MAP particles and HA particles having a flow hole for the water to be treated is provided at the bottom of the tower. A fluidized bed (fluidized bed) 5 is formed. 6 is a pH meter, 7 is p
A pipe for introducing an aqueous solution of NaOH (sodium hydroxide) for adjusting H, and a pipe 8 for introducing an aqueous solution of a magnesium compound such as MgCl ₂ (magnesium chloride).

Raw water is introduced into the lower part of the reaction tower 1 through a pipe 2. Further, an aqueous NaOH solution is injected so that the pH in the tower becomes 7.5 to 9.5. It should be noted that the pH adjustment may be any alkaline agent, and is not limited to an aqueous NaOH solution. However, calcium hydroxide is not suitable because it promotes the precipitation of HA and reduces the recovery rate of MAP.

Further, the Mg / P ratio in the column is 1.0 to 3.0.
The MgCl ₂ aqueous solution is injected so as to fall within the range.
The addition of Mg is not limited to MgCl ₂ , but may be magnesium hydroxide (Mg (OH) ₂ ) or another magnesium compound. Mg (OH)
_{When 2} is used, the alkali for pH adjustment can be made unnecessary or reduced.

In the reaction tower 1, MAP is granulated using the MAP particles of the fluidized bed 5 as seed crystals, and HA is granulated using the HA particles as seed crystals. That is, the MAP particles and the HA particles are brought into a fluidized state by the inflow of the raw water and the circulation of the treated water,
A new M is added to the surface of each of the MAP particles and the HA particles.
AP and HA precipitate, and MAP particles and HA particles grow. The treated water whose phosphorus concentration has decreased due to the precipitation of MAP and HA is discharged from the extraction pipe 3. Part of the treated water is circulated to the lower part of the tower by the circulation pipe 4.

In the present invention, the MAP particles for forming the fluidized bed 5 in the reaction tower 1 have an initial average particle size of 0.1.
The HA particles preferably have a size of about 5 to 2.0 mm, and the HA particles preferably have an initial average particle size of about 0.5 to 2.0 mm. Specifically, phosphate ore particles can be used as the HA particles.

The ratio between the MAP particles and the HA particles in the reaction tower 1 is as follows: MAP particles: HA particles = 19: 1 to 7: 3
(Volume ratio). HA ratio
When the number of MAP particles is small and the amount of MAP particles is large, the effect of promoting the HA crystallization reaction is not sufficiently obtained.

When ammonium ions are insufficient for MAP generation, it is necessary to further add ammonia or ammonium salt to the reaction tower.

The reaction tower shown in FIG. 1 is an example of a reaction tower suitable for carrying out the present invention, and the present invention is not limited to the illustrated one. For example, the reaction tower may be of a type in which particles in the tower are caused to flow by air aeration. Alternatively, the MgCl ₂ aqueous solution may not be directly introduced into the reaction tower, but may be previously mixed with raw water. NaO is added to this raw water in advance.
An H aqueous solution may be mixed and introduced into the reaction tower.

The method for dephosphorizing waste water according to the present invention uses a PO ₄ -P concentration of 20 to ₅ as in the case of the above-mentioned organic sludge dewatered separation liquid.
0 mg / L, NH ₄ -N concentration 30-80 mg / L, Ca
Sludge dewatering / separation at a sludge treatment center that transports and collects and treats wastewater containing NH ₄ —N and Ca with a relatively low PO ₄ —P concentration of about 20 to 100 mg / L, particularly pipes, etc. Suitable for treating liquids.

[0029]

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

Example 1 A reaction tower shown in FIG. 1 (diameter 30 mm, height 2500 mm)
Contains 600 mL of MAP particles (average particle size 0.75 mm) and 100 mL of phosphate rock particles (average particle size 0.75 mm) to form a fluidized bed, and contains MgC as a magnesium compound.
with the addition of l ₂ 280 wastewater had the following water quality as raw water
0 mL / hr was introduced into the reaction tower 1 and the amount of circulating water was 2800
Upstream flowing water was supplied at 5600 mL / hr as mL / hr. Further, a 24 wt% aqueous solution of NaOH was injected into the reaction tower so that the pH of the treated water became 8.7.

[Raw water] The dewatered separation liquid of the organic sludge is further centrifuged at 10,000 G to remove the SS. The supernatant liquid [raw water quality] PO ₄ -P: 35 mg / L Mg: 30 mg / L NH ₄ -N: 50 mg / L Ca: 48 mg / L As a result, the average water quality of the treated water obtained by the continuous treatment for two weeks was as shown in Table 1.

COMPARATIVE EXAMPLE 1 A reaction tower was not filled with phosphate rock particles, and only MAP particles
The treatment was carried out in the same manner as in Example 1 except that the container was accommodated in a volume of 00 mL. The average water quality of the treated water obtained by the continuous treatment for two weeks is shown in Table 1.

[0033]

[Table 1]

From Table 1, it can be seen that by forming a mixed fluidized bed of MAP particles and HA particles in the reaction tower, it is possible to efficiently remove phosphorus and to prevent the outflow of fine particles. It can be seen that SS is also reduced and that treated water of good quality can be obtained.

[0035]

As described in detail above, according to the method for dephosphorizing waste water of the present invention, the MAP method and the HA crystallization method are used.
By efficiently removing phosphorus from wastewater in which phosphate ions, ammoniacal nitrogen and calcium ions coexist in sludge dewatering separation liquid, etc., phosphorus in the wastewater is recovered as MAP, and the PO ₄ -P concentration is reduced. It is possible to obtain high quality treated water which is remarkably low and has low SS. In addition, scale disturbance due to calcium scale is also prevented, and stable processing can be continued for a long time.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a reaction tower used in a method for removing phosphorus from wastewater of the present invention.

[Explanation of symbols]

 Reference Signs List 1 reaction tower 2 raw water introduction pipe 3 treated water extraction pipe 4 circulation pipe 5 fluidized bed 6 pH meter

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Ishizuka 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Co., Ltd. Industrial Co., Ltd. (72) Inventor Fumio Sanpin 2-1-23-307 Kamoricho, Kishiwada-shi, Osaka F-term (reference) 4D038 AA08 AB48 AB51 AB52 AB54 BA02 BB13 BB17

Claims (1)

[Claims] 1. A wastewater containing phosphate ions, ammoniacal nitrogen and calcium ions is allowed to flow upward through a reaction tower, and phosphate ions in the wastewater are removed from the wastewater in the presence of a magnesium compound. A method for dephosphorizing wastewater, which is produced as an insolubilized product of magnesium ammonium phosphate and separates the wastewater, comprising: forming a fluidized bed of magnesium ammonium phosphate particles and hydroxyapatite particles in the reaction tower. Rin method.