JPS59203691A - Dephosphorization - Google Patents

Abstract

PURPOSE:To perform efficient dephosphorization while easily regenerating a crystal seed, by supporting calcium phosphate-contg. powder on a calcium phosphate-contg. crystal seed whose capacity has been deteriorated by bringing it into contact with phosphate-contg. water to perform dephosphorization. CONSTITUTION:Phosphate-contg. water to be treated is brought into contact with a calcium phosphate-contg. crystal seed in the presence of calcium ion under the condition of a pH of 6 or higher, to perform the depohsphorization that phosphoric ion in the water to be treated is crystallized as calcium phosphate. Whe the crystal seed used for said dephosphorization has dephosphorizing power deteriorated by making its surface inactive with magnesium and organic substance in the water to be treated, calcium phosphate-contg. powder is supported on said crystal seed to easily reactivate the crystal seed. A phosphate mineral, boneblack, granular matter having a calcium phosphate crystal on its surface, etc. may be used as said crystal seed, while hydroxiapatite, fluoroapatite, trilime phosphate, a phosphate mineral, etc. may be properly used as said calcium phosphate-contg. powder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing phosphate from water containing phosphate by crystallization.

As a method for removing phosphates contained in tap water, sewage, industrial water, factory wastewater, boiler water, etc., water containing phosphates is treated with crystals containing calcium phosphate such as phosphate rock in the presence of calcium ions. A method of contact with seeds has been proposed. This method removes phosphate ions contained in water by converting them into calcium phosphate such as hydroxyapatite and crystallizing them into crystal seeds. The processing efficiency is also significantly improved.

However, this method has a problem in that when magnesium t1 ions and organic substances are present in the raw water, the surface of the crystal seeds gradually becomes inactive and the dephosphorization performance deteriorates.

As a means to solve these problems, a method has been proposed in which crystal seeds with reduced dephosphorization performance are treated with an acidic solution to be reactivated. The surface of the crystal seeds dissolves in the process, resulting in a large amount of phosphorus being contained in the acidic waste liquid, which poses problems such as the need for additional treatment.

This invention is aimed at solving the problems of conventional methods such as "double crystals", and by supporting powder containing calcium phosphate on crystal seeds with degraded performance, it is possible to reactivate them with a simple operation. The purpose is to provide a method for dephosphorization.

This invention provides dephosphorization performance in a method for dephosphorizing water containing phosphate by crystallization by bringing water containing phosphate into contact with crystal seeds containing calcium phosphate in the presence of calcium ions and under conditions of pH 6 or higher. This is a dephosphorization method characterized by reactivating crystal seeds with reduced phosphorescence by supporting powder containing calcium phosphate.

The reaction that occurs when water containing phosphate is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions varies depending on the reaction conditions, but is usually expressed by the following formula.

5Ca2++311P04''-+408-+Ca5(0
110P04)s+3H20-(1) As seen from equation (1), in order to increase the removal rate of phosphate, it is necessary to advance the reaction to the right, and at the same time, keep the surface of the crystal seeds clean to increase their activity. It is necessary to keep the level high.

Crystal seeds containing calcium phosphate include hydroxyapatite (Ca5(OtI)(PO4)5),
Crystal species containing calcium phosphates such as fluoroapatite (Ca5(F)(PO4)3) or tricalcium phosphate CCa3(PO4)2) can be used, and natural phosphate rock or bone char is mainly composed of these calcium phosphates. Suitable as a crystal seed. Furthermore, crystal seeds in which calcium phosphate is precipitated on the surface of granular materials such as sand or calcium carbonate can also be used. The crystal seed is preferably one whose main component is calcium phosphate of the same type as the calcium phosphate produced by the reaction. For example, in a system that produces hydroxyapatite, the use of hydroxyapatite 1- facilitates the precipitation of new crystals, efficiently removes phosphate, and increases the removal rate.

The raw water to be crystallized by contacting with the crystal seeds containing phosphoric acid as described above is water containing phosphate, and includes secondary treated water such as sewage, human waste, and industrial wastewater. In the present invention, even if these raw waters contain magnesium, organic substances, etc., crystallization can be performed without pre-treating the raw water.

The crystallization conditions are the same as those of the conventional method, and when it is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions and under conditions of pH 6 or higher, the calcium phosphate produced by the above formula (1) becomes a crystal seed. Crystals precipitate on the surface and grow, removing phosphate ions from the water.

Calcium ions and hydroxide ions to be present in water do not need to be added externally if they are present in the raw water from the beginning, but if they are not present in the raw water or are insufficient, they are added externally. The amount added should be in excess of the reaction equivalent, but if too much is added, fine precipitates may precipitate in places other than the crystal seeds, and impurities such as calcium carbonate may be generated. It should be within the range where it will not be generated. That is, the amounts of calcium ions and hydroxyl ions are set to be higher than the solubility of the hydroxyapatite produced in equation (1), but lower than the supersolubility, that is, the conditions are such that hydroxyapatite is produced at a concentration in the metastable range. Here, supersolubility is the concentration at which crystals begin to precipitate when no crystal seeds are present in the reaction system.

In other words, at a concentration higher than supersolubility, new crystals precipitate where crystal seeds do not exist, forming fine precipitates and clogging the filter bed, but in a metastable region lower than supersolubility, new crystals precipitate on top of crystal seeds. New crystals are precipitated and the crystals grow, but no precipitate is formed. In addition, crystals do not precipitate in systems lower than the solubility.

The amount of hydroxyapatite produced is mainly controlled by the phosphate dione concentration, calcium ion concentration, and pH of the reaction system. The amount of calcium ions and the PO value to bring hydroxyapatite within the metastable range can be determined experimentally by changing these values for each reaction system.

The approximate range is when phosphate ion is 50mg/Q or less, calcium ion is IO-100mg/Q.
Q. The pH is about 6 to 12, but it varies depending on the conditions.

The method of contacting the raw water containing phosphate with the crystal seeds containing calcium phosphate may be a fixed bed type or a fluidized bed type. The smaller the size of the crystal seeds, the larger the surface area, which makes it easier for new crystals to precipitate, but if the size of the seeds is too small, it will be difficult to contact or separate the crystal seeds from water. Also, if the particle size is too large, the specific surface area per unit filling amount will be small, so it is usually 9 to 300.
Use something similar to mesh. The larger ones are suitable for fixed beds, and the smaller ones are suitable for fluidized beds. In the case of a fixed bed, the crystal seeds with a particle size of 9 to 35 mesh are packed and the flow rate S
Water is passed in a top flow or a downward flow at VI~5 hr-1 to precipitate calcium phosphate crystals.

If the crystal seed surface becomes contaminated or clogged during water flow, periodically perform upward flow cleaning (backwashing) to expand and clean the crystal seed bed and remove impurities attached to the surface. It is desirable to peel off the Water flow conditions during backwashing are as follows:
The flow rate is about 20 to 80 m/hr, and the washing time is about 5 to 60 minutes.

If the above crystallization operation is continued, especially if the raw water contains impurities such as magnesium ions and organic substances,
The activity of the crystal seeds may decrease and the dephosphorization performance may decrease. Therefore, in the present invention, the crystals with reduced dephosphorizing performance are reactivated by supporting powder containing calcium phosphate to restore the dephosphorizing performance.

As the powder containing calcium phosphate, the above-mentioned crystalline powder containing calcium phosphate can be used, and natural phosphate rock, bone char, crystalline calcium phosphate composite, agglomerated precipitate containing calcium phosphate as a main component, for example, adding calcium to phosphorus-containing water can be used. Powders such as calcium phosphate precipitated can be used.

Note that the crystalline calcium phosphate composite includes a product obtained by reacting phosphate ions and calcium ions and aging the resulting reaction product.

These powders containing calcium phosphate have a particle size of 0.4 mm.
The following (approximately 36 mesh or less) are used, and those originally obtained as powder can be used as they are, but those obtained as granules or lumps are used after being pulverized. As a powdering means, a known means is used.

In order to support powder containing calcium phosphate on crystal seeds with reduced dephosphorization performance, calcium phosphate itself can be used as a binder. In this case, when crystallization is performed with the crystal seeds and the powder in contact with each other, the precipitated calcium phosphate acts to bind the crystal seeds and the powder.

As a result, the powder is supported on the crystal seeds using the precipitated crystals as a binder.

In order to support a powder containing calcium phosphate by such a method, a suspension of powder containing calcium phosphate 11 is circulated through a fixed bed filled with crystal seeds until most of the suspended matter is removed, and then the above-mentioned method is carried out. The powder is trapped in a fixed bed of crystal seeds.

As the liquid for suspending the powder, two bottles of industrial water,
Treated water or raw water can be used, and the water can be passed in two directions or in a downward direction, but downward flow is preferable because it allows powder to be captured uniformly, and the smaller the amount of liquid used, the better the equipment and Preferable from an energy standpoint. The amount of powder to be supplied is approximately 1 g of powder per 50 to 500 g of the support.

When water containing phosphate is passed through a fixed bed of crystal seeds containing powder containing calcium phosphate under conditions of pH 6 or higher, preferably in the presence of calcium ions, in a vortex or circulation manner, phosphoric acid Calcium 11 is precipitated so as to bridge the crystal seeds and the powder, and the powder is supported on the support. In order to support the powder on the crystal seeds, it is desirable to pass water containing phosphate for several days to several tens of days, and the amount of powder supported is determined by the water passing time. The phosphate-containing water used for crystallization may be the raw water to be treated, but a concentrated phosphate solution may be used to shorten the contact time.

The powder loading rate for crystal seeds is 1 mg phosphorus per 1 g.
It is preferable to set it as above. In order to support this amount of phosphorus, it varies depending on the conditions, but generally the crystallization is
~25EI or more'' - just do it. The crystallization conditions for supporting the powder may be the same as the crystallization conditions for dephosphorization described above.

When a solution containing a low concentration of phosphate is used, the solution flowing out from the crystal seed layer does not contain phosphorus and can be released as is, but when a solution with a high phosphorus concentration is used, phosphorus is eluted. In some cases, it can be recycled or recovered for use in the next reactivation, and in the case of low-concentration effluent, it can be returned to the raw water line for dephosphorization.

After supporting the powder on the surface of the crystal seeds, it becomes a packed layer of crystal seeds.
- When fresh water such as water is passed upward to develop a packed bed,
Unsupported powder is removed to allow reactivation of crystal seeds. 1.1 The powder can be separated by filtration, etc., and recycled for reuse. The powder treated with In-11c may be used for subsequent reactivation, or may be used as fertilizer, etc.

Unsupported powder does not necessarily need to be removed. If reactivation 1 is carried out in a separate column, it will inevitably be removed, but if reactivation is carried out in the same column, a sand filtration device or similar device is installed before the crystallization tank to remove suspended matter. By arranging the means, dephosphorization can be performed while the powder is trapped in the crystal seed layer without removing it.

The powder containing calcium phosphate supported on the crystal seeds becomes a nucleus for crystallization during subsequent dephosphorization, so before or after supporting the powder on the crystal seeds, a concentrated slaked lime solution, a chlorine agent-containing solution (chlorinated water, It is also possible to further increase the activity by performing another activation treatment by contacting the product with sodium hypochlorite, salami powder, highly salami powder solution, etc.) or an aqueous alkali agent solution.

The crystal seeds that have been reactivated as described above are again subjected to dephosphorization, and dephosphorization can be performed by the same crystallization operation as described above. If the dephosphorization performance becomes low again, reactivation can be performed by the same operation and this process can be repeated.

As described above, according to the present invention, since the crystal seeds with degraded performance are reactivated by supporting powder containing calcium phosphate, Crystal seeds can be refigured, the effluent during reactivation does not require special treatment, and reactivation is more effective! 1', dephosphorization can be continued.

Next, examples of the present invention will be described.

Example Magnesilla 11 ion /IQ ~ 60mg/U, sulfate ion 1.50-250mg/Q, 'J Nwo] -
'4' used for about 2 years for dephosphorization by crystallization of secondary treated sewage water containing 2mH/Q; 3
It was packed into an acrylic resin column with a diameter of 0 mm and a cavity of 500 m+n. This packed bed has an O'17 diameter of 0. A suspension of 2 g of hydroxyapatite powder of 1 mm or less in 500 m O tap water was circulated through the water at a flow rate of 50 to 127 m O to fill it with the I'0 end of hydroxyapatite. It was captured by Fm. Then, the phosphorus concentration was 20 mg.
/ Q, total 7 ruiJ 'J degree approx.], OOmg/
Q (7) Continuously add 1-1 parts of calcium chloride aqueous solution and 1-wow 11 hydroxide solution to synthetic water to bring the calcium ion concentration to about 45 m(</D,
, After adjusting the pH to 8.8-9.0,
Water was passed through the packed bed for 3 days in an upward flow at a flow rate of 300 m Q /hr. 3rd move F3 water flow was stopped, the packed bed of phosphate rock crystal seeds was expanded and washed (backwashed) with tap water of about IQ, and the unsupported powder was discharged outside the packed bed, and the reactivation was completed. .

Next, the phosphorus concentration is 2 mg/Q, and the total alkalinity is about 100 m.
g/Q of synthetic water was continuously added with a calcium chloride aqueous solution and a sodium hydroxide aqueous solution at the column inlet to obtain a calcium ion concentration of approximately 45 mg/Q and a pi of 8.8 to 9.0.
After adjusting to
Water was continuously passed through the packed bed for 30 days at a flow rate of r to perform dephosphorization by crystallization.

Table 1 shows the phosphorus concentration and pi of the treated water during the water flow period. As a comparative example, Table 1 also shows the treatment results when the same phosphate rock was used for dephosphorization under the same conditions without being reactivated.

Table 1 As shown in Table 1, the average phosphorus concentration in the treated water without reactivation is close to mg/Q, and the pH is 8.5 or higher, while the average phosphorus concentration in the case of reactivation is close to mg/Q. Phosphorus concentration is 0.5
It can be seen that the dephosphorization performance is lower than mg/Q and pl+ is lower than 8.5. The phosphorus concentration of the effluent during the reactivation process was 2 to 6 mH/Q, and the pH was 8.
It was 7-8,9. Upon completion of reactivation, the unsupported powder is discharged, and the powder is easily sedimented and separated by standing, and the supernatant has a phosphorus concentration of 2.0 rng/Q.
, pH was 7.3.

From the results of above-L, dephosphorization of 1M can be achieved by reactivation treatment.
It can be seen that there is a remarkable recovery.

Agent: Patent attorney Sei Yanagi Hara

Claims (1)

[Claims] (],) Water containing phosphate is brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions and under conditions of pl+6 or more to dephosphorize by crystallization. A dephosphorization method characterized in that the crystal seeds with reduced dephosphorization performance are reactivated by supporting powder containing calcium phosphate. (2) The dephosphorization method according to claim 1, wherein the crystal seeds are phosphate rock, bone char, or granules having calcium phosphate crystals on the surface. (3) Powders containing calcium phosphate include hydroxyapatite, fluoroapatite, tricalcium phosphate, phosphate rock,
The dephosphorization method according to claim 1 or 2, wherein the dephosphorization method is bone char or a coagulated precipitate whose main component is calcium phosphate. (4) The dephosphorization method according to any one of claims 1 to 3, wherein the powder containing calcium phosphate is supported using calcium phosphate as a binder.