JP2001314874A - Apparatus and method for treating phosphorus- containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the outflow of fine calcium phosphate particles from a calcium phosphate crystallization reaction column and the formation of scale in the column, in an apparatus and method for treating phosphorus-containing water by removing and recovering phosphate groups in phosphorus-containing water as calcium phosphate. SOLUTION: In the phosphorus-containing water treatment apparatus equipped with a mixing tank for mixing phosphate group-containing water, a water soluble calcium compound and a pH controller and a crystallization reaction column having the introducing port of the outflow liquid of the mixing tank disposed at the lower part thereof and having a treated water outflow port disposed at the upper part thereof and housing seed crystals, a seed crystal return means for returning seed crystals in the crystallization reaction column to the mixing tank is provided. In the phosphorus-containing water treatment method, phosphate group-containing water, the water soluble calcium compound and the pH controller are mixed in the presence of seed crystals in the mixing tank to be introduced into the lower part of the crystallization reaction column and treated water is allowed to flow out of the upper part of the reaction column and the seed crystals in the crystallization reaction column are returned to the mixing tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an apparatus and a method for treating phosphorus-containing water. More specifically, the present invention relates to a treatment apparatus and a treatment method for removing and recovering phosphate groups in phosphorus-containing water as calcium phosphate, wherein the fine calcium phosphate particles flow out from the calcium phosphate crystallization reaction tower and the inside thereof. The present invention relates to a phosphorus-containing water treatment device and treatment method capable of preventing scale formation.

[0002]

2. Description of the Related Art As a method for removing phosphorus from phosphorus-containing water such as sewage and wastewater, there are a coagulation sedimentation method, an adsorption method, and a crystallization method. In the coagulation sedimentation method using an iron salt or an aluminum salt, a large amount of sludge is generated. Coagulation by calcium salts requires a large amount of calcium salts, and furthermore, scales are easily formed in order to make the pH strongly alkaline, and neutralization of treated water is required. In addition, in the adsorption method, the amount of adsorption is limited by the adsorbent, and it is necessary to replace or regenerate the adsorbent when the adsorption is saturated. In contrast, the crystallization method enables semi-permanent continuous operation,
The feature is that the amount of generated sludge can be reduced. As a crystallization method for removing phosphorus from a phosphorus-containing wastewater to 1 mg P / L or less, there is a calcium phosphate crystallization method. In this method, phosphorus in a liquid is precipitated and removed as calcium phosphate by bringing it into contact with a seed crystal containing calcium phosphate in the presence of calcium ions and at a pH of 6 or more. The reaction that takes place at this time depends on the reaction conditions, but is usually represented by the following formula. 5Ca ²⁺ + 3HPO ₄ ^2- + 4OH ⁻ → Ca ₅ (PO ₄ ) ₃ OH + 3H ₂ O [1] The amount of calcium ions and hydroxyl ions present in water is set to be larger than the reaction equivalent. If present in a large amount, fine precipitates will be deposited in places other than the seed crystal,
Impurities such as calcium carbonate may be generated. Therefore, it is necessary to add a calcium salt or an alkali agent to the water to be treated so as to suppress generation of fine particles and to precipitate calcium phosphate only on the surface of the seed crystal. In a method in which the water to be treated is mixed with a calcium salt or an alkaline agent and then brought into contact with a seed crystal in the reaction tower, it is necessary to suppress the conditions such that fine particles are not generated before flowing into the reaction tower. In this method, the calcium ion concentration at the inlet of the reaction tower,
In some cases, the pH conditions are limited, and the quality of the treated water and the requirement for limiting the volume of the reaction tower cannot be satisfied. In order to reduce the size of the reaction apparatus, that is, to speed up the reaction, it is necessary to increase at least one of the calcium ion concentration and the pH, but there are limitations as described above. When a calcium salt and an alkali agent are added in the presence of a seed crystal, the generation of fine particles other than the surface of the seed crystal can be suppressed as compared with a state without the seed crystal. If the drug is added immediately before contacting with or within the seed crystal layer, there is a risk of generating a density flow, and the diffusion of the drug cannot be controlled well. In addition, if priority is given to the diffusion of the drug in the seed crystal layer, the inside of the reaction tower approaches a completely mixed state, and the treatment efficiency is reduced, or a separate means for separating the seed crystal and the treated water is required. There was a problem.

[0003]

DISCLOSURE OF THE INVENTION The present invention relates to an apparatus and a method for treating phosphorus-containing water for removing and recovering phosphate groups from the phosphorus-containing water as calcium phosphate. Another object of the present invention is to provide an apparatus and method for treating phosphorus-containing water that can prevent scale formation in a tower.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the crystallization reaction tower was added to a mixing tank of phosphorus-containing water, a water-soluble calcium compound and a pH adjuster. By returning the seed crystal and mixing in the presence of the seed crystal, the outflow of fine particles from the calcium phosphate crystallization reaction tower and the generation of impurities can be suppressed, and more efficient dephosphorization becomes possible. And completed the present invention on the basis of this finding. That is, the present invention has (1) a mixing tank of water containing a phosphate group, a water-soluble calcium compound and a pH adjuster, and an inlet for an effluent of the mixing tank at the bottom of the tower;
In a treatment device for phosphorus-containing water having an outlet for treated water at the top of the tower and a crystallization reaction tower containing a seed crystal, the seed crystal in the crystallization reaction tower is returned to the mixing tank. An apparatus for treating phosphorus-containing water, comprising a seed crystal returning means,
(2) A method for treating a phosphorus-containing water in which a water-soluble calcium compound and a pH adjuster are added to water containing a phosphate group, and the phosphorus compound is crystallized and removed. And the pH adjuster are mixed in a mixing tank in the presence of the seed crystal, and then introduced into the lower portion of the crystallization reaction tower containing the seed crystal, and water is passed through the crystallization reaction tower while crystallizing the phosphorus compound. And (3) a seed crystal concentration in the mixing tank, wherein the treated water is discharged from the upper part of the reaction tower, and a seed crystal in the crystallization reaction tower is returned to the mixing tank. 3. The method for treating phosphorus-containing water according to claim 2, wherein the seed crystals in the crystallization reaction tower are returned to the mixing tank so that the content of the phosphorus is 1 to 30% by weight. Further, as a preferred embodiment of the present invention, the method for treating phosphorus-containing water according to claim 2, wherein (4) the water-soluble calcium compound is added so that calcium is added in an amount of 2 to 20 times by mole of phosphorus.
(5) Adjust the pH so that the effluent of the mixing tank has a pH of 7 to 12.
3. The method for treating phosphorus-containing water according to claim 2, wherein a regulator is added.
And (6) the method for treating phosphorus-containing water according to item 2, wherein the seed crystal has an average particle size of 0.05 to 1 mm.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The apparatus for treating phosphorus-containing water according to the present invention comprises water containing a phosphate group and a water-soluble calcium compound.
A mixing tank with a pH adjuster, a crystallization reaction tower having an inlet for the effluent of the mixing tank at the bottom of the tower, an outlet for treated water at the top of the tower, and containing a seed crystal. The apparatus for treating phosphorus-containing water has a seed crystal returning means for returning seed crystals in the crystallization reaction tower to the mixing tank. In the method for treating phosphorus-containing water of the present invention, the method for treating a phosphorus-containing water comprises adding a water-soluble calcium compound and a pH adjuster to water containing a phosphate group, and crystallizing and removing the phosphorus compound. The water, the water-soluble calcium compound and the pH adjuster are mixed in a mixing tank in the presence of seed crystals, and then introduced into the lower portion of the crystallization reaction tower containing the seed crystals, and the phosphorus compound is crystallized while crystallizing. Water is passed through the precipitation reaction tower, and the treated water is allowed to flow out of the upper part of the reaction tower, and the seed crystals in the crystallization reaction tower are returned to the mixing tank. FIG. 1 is a process flow diagram of one embodiment of the apparatus of the present invention. Raw water is fed into the mixing tank 1, and seed crystals are returned from the seed crystal packed bed 3 formed in the crystallization reaction tower 2 through the seed crystal return pipe 4. A water-soluble calcium compound and a pH adjuster are further added to the mixing tank, and are uniformly mixed by stirring. As shown in FIG. 1, the addition amount of the pH adjuster can be controlled by providing a pH meter in the mixing tank, or by providing a pH meter at the inlet of the reaction tower. The effluent from the mixing tank is led to the effluent inlet at the bottom of the reaction tower through the effluent pipe 5. In the reaction tower, a seed crystal packed bed 3 is formed, and the effluent of the mixing tank in which calcium phosphate is in a supersaturated state flows upward in the tower while crystallizing calcium phosphate on the surface of the seed crystal. It flows into treated water having a low phosphorus concentration and flows out from an outlet provided at the top of the tower.

The water-soluble calcium compound used in the method of the present invention is not particularly limited. Examples thereof include calcium chloride, calcium bromide, calcium iodide, calcium nitrite, calcium nitrate, calcium sulfate, calcium chlorate, and calcium hypochlorite. , Inorganic calcium salts such as calcium phosphinate, calcium formate, calcium acetate, calcium propionate, calcium acetylsalicylate,
Organic calcium salts such as calcium phenolsulfonate and calcium hydroxide can be mentioned. In the method of the present invention, the amount of the water-soluble calcium compound to be added is not particularly limited.
It is preferably a molar ratio, more preferably 5 to 15 times. That is, it is preferable to add 1.2 to 12 times the water-soluble calcium compound, and more preferably 3 to 9 times the water-soluble calcium compound, of the theoretical amount represented by the chemical reaction formula [1]. . If the ratio of calcium to phosphorus is less than 2 molar times, the phosphorus concentration of the treated water may not be sufficiently reduced. If the ratio of calcium to phosphorus exceeds 20 mol times, the quality of treated water may be reduced due to excessive calcium. There is no particular limitation on the pH adjuster used in the method of the present invention, for example,
Sodium hydroxide, potassium hydroxide, sodium carbonate,
Potassium carbonate, ammonia and the like can be mentioned.
When calcium hydroxide is used as the water-soluble calcium compound, calcium hydroxide can also serve as a pH adjuster. The pH adjuster is preferably added so that the effluent of the mixing tank has a pH of 7 to 12,
More preferably, it is added so as to be from 10 to 10. The pH of the effluent of the mixing tank can be measured at any point between the mixing tank and the inlet of the crystallization reaction tower. The addition amount of the pH adjuster can be controlled based on the measured value of the pH of the effluent of the mixing tank.

[0007] The apparatus of the present invention incorporates a seed crystal in a crystallization reaction tower. The substance used as the seed crystal is a substance generated by the reaction between the phosphate group in the phosphorus-containing water and the added water-soluble calcium compound or a substance similar thereto, such as apatite such as hydroxyapatite, fluorapatite, and chloroapatite. Calcium phosphate such as tricalcium phosphate can be used as a seed crystal, or a substance containing calcium phosphate as a main component such as natural phosphate rock and bone charcoal can be used as a seed crystal. In addition, on the surface of filter media such as sand,
Seed crystals on which calcium phosphate is precipitated can also be used. It is preferable that the seed crystal is mainly composed of the same kind of calcium phosphate as calcium phosphate generated by the reaction. When the operation of the apparatus of the present invention is started, the lower part of the crystallization reaction tower is filled with a seed crystal, and the seed crystal is also added to the phosphorus-containing water in the mixing tank. Stir the mixing tank to disperse the seed crystals in water in a slurry state, feed in phosphorus-containing water, add a predetermined amount of a water-soluble calcium compound, and adjust the pH of the effluent of the mixing tank to a predetermined value. Add modifier. The effluent from the mixing tank is led to the effluent inlet at the bottom of the crystallization reaction tower through the effluent piping. Since a seed crystal packed bed is formed in the crystallization reaction tower, the effluent of the mixing tank in which calcium phosphate is supersaturated flows upward while crystallizing calcium phosphate on the surface of the seed crystal. It flows as a stream, becomes treated water with a low phosphorus concentration, and flows out from an outlet provided at the top of the tower. The seed crystals contained in the effluent of the mixing tank and carried to the crystallization reaction tower are returned from the crystallization reaction tower to the mixing tank. There is no particular limitation on the method of returning the seed crystal to the mixing tank, for example,
A method using a pump, a method using an air lift, and the like can be used. If the operation of the apparatus of the present invention is continued for a long period of time, the amount of seed crystals gradually increases. Therefore, it is preferable to appropriately discharge some of the seed crystals to the outside of the system. There is no particular limitation on the method of discharging a part of the seed crystal out of the system. For example, a seed crystal outlet can be provided at the lower part of the crystallization reaction tower, or a branch pipe is provided in the seed crystal return pipe to discharge the seed crystal. You can also.

In the method of the present invention, the seed crystal concentration in the mixing tank is preferably from 1 to 30% by weight, more preferably from 5 to 20% by weight. If the seed crystal concentration in the mixing tank is less than 1% by weight, fine calcium phosphate particles may be generated. If the seed crystal concentration in the mixing tank exceeds 30% by weight, the power consumption required for stirring and transfer increases, and crystals may be deposited in the piping. The reaction rate of calcium phosphate formation is increased by increasing at least one of the calcium ion concentration and the pH, but these setting conditions are limited in order to suppress the formation of fine particles as described above. However, in the present invention, since the water-soluble calcium compound and the pH adjuster are added to the mixing tank, these agents can be rapidly stirred to rapidly diffuse these agents, and since seed crystals are present, Even when the calcium ion concentration and the pH are increased, the precipitation of calcium phosphate occurs on the seed crystal surface, and the generation of fine particles can be suppressed. In addition, the mixing tank is in a completely mixed state to diffuse the drug, and the seed crystals in the mixing tank flow out together with the effluent and flow into the crystallization reaction tower. Precipitates, and solid-liquid separation of treated water and seed crystals can be easily performed. In the method of the present invention, the average grain size of the seed crystals is not particularly limited, but is preferably 0.05 to 1 mm, more preferably 0.1 to 0.5 mm. If the average particle size of the seed crystal is less than 0.05 mm, it is difficult to completely separate the solid and liquid, and there is a possibility that the fine seed crystal may be mixed into the treated water. If the average particle size of the seed crystal exceeds 1 mm, the surface area on which calcium phosphate is precipitated becomes small, and fine crystals may be deposited on the surface other than the surface of the seed crystal. According to the apparatus and method for treating phosphorus-containing water of the present invention, the calcium ion concentration and the pH in the mixing tank can be increased, so that the reaction time for the phosphorus concentration of the treated water to reach a predetermined concentration can be reduced. Thus, it is possible to prevent the outflow of fine calcium phosphate particles from the calcium phosphate crystallization reaction tower and the formation of scale in the tower, and to effectively remove and recover phosphate groups in the phosphorus-containing water as calcium phosphate.

[0009]

The present invention will be described in more detail with reference to the following examples.
However, the present invention is not limited to these examples.
It is not specified. In Examples and Comparative Examples,
The phosphate ion is compliant with JIS K 0102 46.1.1.
Therefore, it was quantified and total phosphorus was determined according to JIS K 0102 46.
Quantification according to 3.1. Example 1 Raw water containing 3 mg P / L of phosphate ions as phosphorus was
Dephosphorization using apatite as a seed crystal using an apparatus similar to Fig. 1.
Processing was performed. The mixing tank has a capacity of 100 mL and is inside the mixing tank.
In the reaction tower so that the concentration of apatite is 10% by weight.
Returned apatite. The reaction tower is 30mm in diameter and height
2,000 mm in height, apatite with an average particle size of 0.2 mm
Filled up to 100 mm. 7.5L / hr of raw water in mixing tank
(SV5hr for the total volume of mixing tank and reaction tower)^-1) Feed
And agitate the aqueous calcium chloride solution
Add the solution to a concentration of 40 mg Ca / L, and add
Sodium hydroxide solution so that the pH of water becomes 9.5
The liquid was added. The effluent of the mixing tank is reacted from the bottom of the reaction tower
The water was sent to the tower, and treated water was allowed to flow out from the upper part of the reaction tower. place
The water quality of the water is 0.4 mg / L of total phosphorus (TP), phosphoric acid
Ionic phosphorus (PO_Four ^3--P) 0.3 mg / L. Comparative Example 1 Except not returning apatite from the reaction tower to the mixing tank
Was subjected to a dephosphorization treatment in the same manner as in Example 1. sand
That is, a source containing 3 mg P / L of phosphate ions as phosphorus.
Water is fed into the mixing tank at a rate of 7.5 L / hr.
Calcium iodide aqueous solution with calcium concentration of 40mgCa / L
And adjust the pH of the water at the inlet of the reactor to 9.5.
An aqueous solution of sodium hydroxide was added to the mixture. Mixing tank
Effluent is 30 mm in diameter and 2,000 mm in height, average particle size
Reaction filled with apatite 0.2mm in diameter up to 100mm in height
Sent from the bottom of the tower, and the treated water
I let you. The quality of the treated water is 1.7 mg / kg of total phosphorus (TP).
L, phosphate ionic phosphorus (PO_Four ^3--P) at 0.4 mg / L
there were. Table 1 shows the results of Example 1 and Comparative Example 1.
You.

[0010]

[Table 1]

As shown in Table 1, in Example 1 in which apatite in the reaction tower was returned to the mixing tank, the phosphorus concentration of the treated water was low, and phosphorus was effectively removed. On the other hand, in Comparative Example 1 in which the apatite was not returned to the mixing tank, the concentration of the phosphate ion phosphorus was reduced, but the total phosphorus concentration was high, and the generation of fine particles was reduced. You can see that there are many.

[0012]

According to the apparatus and method for treating phosphorus-containing water of the present invention, the outflow of fine calcium phosphate particles from the calcium phosphate crystallization reaction tower and the formation of scale in the tower are prevented, and the phosphorus in the phosphorus-containing water is prevented. The acid radical can be effectively removed and recovered as calcium phosphate.

[Brief description of the drawings]

FIG. 1 is a process flow diagram of one embodiment of the apparatus of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mixing tank 2 crystallization reaction tower 3 seed crystal packed bed 4 seed crystal return pipe 5 effluent pipe

Claims (3)

[Claims] 1. A mixing tank of water containing a phosphate group, a water-soluble calcium compound and a pH adjuster, an inlet for an effluent of the mixing tank at a lower part of the tower, and an outlet of treated water at an upper part of the tower. Have
A phosphorus-containing water treatment apparatus having a crystallization reaction tower having a built-in seed crystal and a seed crystal returning means for returning a seed crystal in the crystallization reaction tower to the mixing tank. Equipment for treating contained water. 2. A method for treating phosphorus-containing water, wherein a water-soluble calcium compound and a pH adjuster are added to water containing a phosphate group to crystallize and remove the phosphorus compound. The calcium compound and the pH adjuster are mixed in a mixing tank in the presence of the seed crystal, and then introduced into the lower portion of the crystallization reaction tower containing the seed crystal.The phosphorus compound is crystallized while passing through the crystallization reaction tower. A method for treating phosphorus-containing water, comprising watering the treated water from the upper part of the reaction tower, and returning the seed crystals in the crystallization reaction tower to the mixing tank. 3. The method for treating phosphorus-containing water according to claim 2, wherein the seed crystals in the crystallization reaction tower are returned to the mixing tank so that the seed crystals in the mixing tank have a concentration of 1 to 30% by weight.