JPH0233435B2 - RINSANENOFUKUMUMIZUNOSHORIHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating water containing phosphate to remove phosphate.

As a method for removing phosphates from water, a method has been proposed in which water containing phosphates is brought into contact with a crystal species containing calcium phosphate, such as phosphate rock, in the presence of calcium ions. This method removes phosphate ions contained in water by converting them into calcium phosphate, such as hydroxyapatite, and crystallizing them into crystal seeds. , processing efficiency will also be significantly improved.

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
It is usually expressed by the following equation.

5Ca ²⁺ +3HPO ₄ ^2- +4OH ^- →Ca ₅ (OH) (PO ₄ ) ₃ +3H ₂ O...(1) As can be seen from equation (1), in order to increase the phosphate removal rate, the reaction must be It is necessary to advance to the right, and at the same time it is necessary to increase the activity of the crystal seeds.

In the reaction of equation (1), calcium ions and hydroxide ions that are present in water do not need to be added externally if they are already present in the raw water, but
If it is not present in the raw water or is insufficient, it is added externally. The amount added is said to 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 formed. It is said that it is not allowed. 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, ie, 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 concentrations higher than supersolubility, new crystals precipitate where crystal seeds do not exist, forming fine precipitates and clogging the bed, but in a metastable region lower than supersolubility, crystals form 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.

By the way, with this method, if the phosphorus concentration in the raw water is relatively stable, it is easy to set the calcium ion concentration and PH according to the phosphorus concentration and maintain it in the metastable range. , it is possible to maintain stable treatment effects.

However, when the phosphorus concentration in raw water fluctuates in short cycles, the metastable region changes accordingly, so calcium agents and alkalis are It is difficult to control the amount of the agent added and always perform crystallization in the metastable region, resulting in the problem that the treatment effect becomes unstable.

In addition, if the phosphorus concentration in the raw water exceeds the set conditions, the condition will be in an unstable region, so some of the phosphates in the raw water will precipitate due to a coagulation reaction and form a crystal seed packed bed.
It was captured as SS, and it was necessary to increase the water flow resistance of the crystal seed packed bed and increase the frequency of cleaning the crystal seed packed bed. As the frequency of cleaning increases, the amount of work required increases, and the treatment effect worsens due to disturbances in the state of crystal seed filling caused by cleaning.Furthermore, the trapped SS phosphorus is discharged into the cleaning wastewater. However, there were problems such as the need to reprocess cleaning wastewater.

This invention is aimed at improving the problems of the conventional method as described above. By bringing the raw water into contact with a phosphorus adsorbent prior to crystallization, phosphorus can be improved even in raw water whose phosphorus concentration fluctuates in short cycles. It is an object of the present invention to provide a method for treating water containing phosphate, which can average the concentration, thereby stably crystallize it, and efficiently dephosphorize it.

This invention is characterized in that water containing phosphate is brought into contact with a phosphorus adsorbent and then brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions and at a pH of 6 or higher. This is a method for treating water containing salt.

Examples of phosphorus adsorbents include activated alumina, magnesia-based adsorbents, phosphate rock, bone charcoal, coral fossils, and ion exchange resins. This phosphorus adsorbent has the property of adsorbing phosphorus (orthophosphoric acid) in the liquid, and this phosphorus adsorption ability varies depending on the phosphorus concentration in the liquid. In other words, under conditions where the phosphorus concentration in the liquid is high, the amount of phosphorus adsorbed increases, under conditions where the phosphorus concentration in the liquid is low, the amount of phosphorus adsorbed decreases, and when the phosphorus concentration further decreases, the amount of phosphorus adsorbed increases. Phosphorus is eluted from the adsorbent into the liquid. Therefore, when raw water whose phosphorus concentration fluctuates is brought into contact with such a phosphorus adsorbent, the fluctuation width of the phosphorus concentration becomes small and the phosphorus concentration in the liquid is averaged out to be approximately constant.

The particle size of the phosphorus adsorbent varies depending on the type, but in general, particles of about 4 to 300 mesh can be used. Among these, larger ones are suitable for fixed beds, and smaller ones are suitable for fluidized beds. For fixed layer, 4 to 35
Filled with phosphorus adsorbent of mesh particle size, flow rate SV2
Make contact by passing the liquid in an upward or downward flow at ~10 hr ^-1 . In the case of a fluidized bed, 9 to 300 meshes of phosphorus adsorbent are used and contact is made with an upward flow of LV1 to 50 m/hr.

When raw water is brought into contact with a phosphorus adsorbent, pretreatment such as SS removal can be performed if necessary. The contact can be carried out in a one-time manner by providing a phosphorus adsorbent packed bed in the raw water supply line, but it is also possible to connect the raw water layer and the phosphorus adsorbent packed bed in a circulating manner. If the surface of the phosphorus adsorbent packed layer is contaminated or clogged, it can be cleaned by spreading upward flow in the same manner as the crystal seed layer described below, but there is no need to regenerate the adsorption capacity.

After bringing it into contact with a phosphorus adsorbent packed bed to average the phosphorus concentration, a crystallization operation is subsequently performed using a crystal seed containing calcium phosphate. In this case, since the phosphorus concentration at the inlet of the crystallization layer becomes a substantially stable concentration, processing in the metastable region can be performed even if the crystallization conditions are set substantially constant.

Crystal species containing calcium phosphate include hydroxyapatite [Ca ₅ (OH) (PO ₄ ) ₃ ], fluoroapatite [Ca ₅ (F) (PO ₄ ) ₃ ], or tricalcium phosphate [Ca ₃ (PO ₄ ) ₂ Crystal seeds containing calcium phosphate, such as . Furthermore, crystal seeds in which calcium phosphate is precipitated on the surface of a material such as sand 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 facilitates the precipitation of new crystals and efficiently removes phosphates.
Removal rate increases.

The crystallization conditions are the same as those of the conventional method, and when brought into contact with crystal seeds containing calcium phosphate in the presence of calcium ions and at a pH of 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.

The amount of hydroxyapatite produced depends on the phosphate ion concentration, calcium ion concentration, and
The amount of calcium ions and the PH value that bring the amount of hydroxyapatite produced within the metastable range, which are controlled by the PH, can be determined experimentally by changing these values for each reaction system. The approximate range is when phosphate ion is less than 50mg/
Calcium ion 10-100mg/, PH 6-12
However, it varies depending on each condition.

The method of contacting the 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. Furthermore, if the particle size is too large, the specific surface area per unit filling amount will be small, so particles of about 9 to 300 mesh are usually used. Among these, the larger one is suitable for a fixed bed, and the smaller one is suitable for a fluidized bed. In the case of a fixed bed, it is filled with crystal seeds having a grain size of 9 to 35 meshes, and water is passed upwardly or downwardly at a flow rate of SV1 to 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 to develop and clean the crystal seed layer and peel off impurities attached to the surface. is desirable. Water flow conditions during cleaning include a flow rate of approximately 20 to 80 m/hr;
The washing time is about 5 to 60 minutes. By cleaning such crystal seeds, SS components are removed, and water flow can be restarted.

After repeating crystallization and washing, if the dephosphorization efficiency does not recover even after washing, a treatment for reactivating the crystal seeds can be performed. This treatment method includes, for example, contacting the crystal seeds with a solution containing a chlorine agent or calcium compound during or after cleaning, or draining and drying after cleaning, which activates the surface of the crystal seeds. This increases the dephosphorization efficiency.

In addition, prior to the above crystallization, SS removal from the raw water,
There is no problem in performing pre-treatment such as organic matter removal or post-treatment such as sterilization.

As explained above, according to this invention,
After contacting the phosphate-containing water with the phosphorus adsorbent,
Since the structure is configured to perform crystallization, the phosphorus concentration of raw water is averaged, and even for raw water whose concentration fluctuates in short cycles, crystallization is always performed stably under conditions in the metastable region, and crystal seed filling is performed. Effects such as being able to perform dephosphorization treatment efficiently without increasing the frequency of cleaning the layer can be obtained.

Next, examples of the present invention will be described.

Example: Coral fossils, activated alumina, bone charcoal, and phosphate rock each having a particle size of 0.5 to 1.0 mmφ were packed as phosphorus adsorbents into separate acrylic resin columns with an inner diameter of 30 mm and a length of 500 mm to form a phosphorus adsorbent layer. As a result of passing synthetic water (does not contain calcium ions) adjusted to a phosphorus concentration of 2 mg/day over this for approximately one month at a flow rate of SV2hr ^-1 , the amount of phosphorus adsorbed by phosphate rock was almost at equilibrium. The phosphorus concentration in the treated water reached a value comparable to the inlet phosphorus concentration. Water was passed through this phosphorus adsorbent layer for 3 hours while changing the phosphorus concentration of the raw water to 3 mg/. After that, when the phosphorus concentration was returned to 2 mg/Water treatment, the phosphorus concentration of the water treated with the adsorbent layer was 1.8.
~1.9mg/, which remained almost constant regardless of changes in the phosphorus concentration of raw water.

On the other hand, phosphate rock with a grain size of 32 to 60 mesh was placed as a crystal seed in an acrylic resin column of the same shape as above.
ml each to form a crystallized dephosphorization layer.

Next, phosphorus concentration 2 mg/, alkalinity 100 mg/
The water containing the above was passed in an upward flow at SV2hr ^-1 through each of the phosphorus adsorbent layers that had reached the above equilibrium, and then the calcium ions were adjusted to 40mg/pH and PH9.0, and then each of the above In the crystallization dephosphorization layer
SV2hr ^-1 , water was passed in an upward flow. 3 hours after the start of water flow, only the phosphorus concentration of the raw water was changed to 5 mg/h, and after water flow for 3 hours, the phosphorus concentration was changed again to 2.
mg/, and water flow was continued. Such operations were repeated and the water flow test was continued for one week.
As a result, no matter which phosphorus adsorbent is used,
The average phosphorus concentration in the effluent from the crystallization dephosphorization layer is 0.40mg/
It became.

For comparison, a test was conducted under the same conditions for one week without water flowing through the phosphorus adsorbent layer, and only through the crystallization dephosphorization layer, and the average phosphorus concentration in the effluent water was
It was observed that a large amount of fine crystals recognized as calcium phosphate were generated at the inlet of the crystallization dephosphorization layer.

From the above results, it can be seen that the method of the present invention can suppress the generation of fine crystals and reduce the number of times of backwashing, and the quality of treated water is also significantly improved compared to the conventional method.

Claims (1)

[Scope of Claims] 1. After bringing water containing phosphate into contact with a phosphorus adsorbent, in the presence of calcium ions and at a pH of
1. A method for treating water containing phosphate, comprising bringing it into contact with crystal seeds containing calcium phosphate under conditions of 6 or more. 2. The phosphate-containing water according to claim 1, wherein the phosphorus adsorbent is one or more selected from activated alumina, magnesia-based adsorbent, phosphate rock, bone char, coral fossil, and ion exchange resin. processing method. 3. The method for treating water containing phosphate according to claim 1 or 2, wherein the phosphorus adsorbent is contacted in a fixed bed or a fluidized bed. 4. The water containing phosphate according to any one of claims 1 to 3, wherein the crystal seeds containing calcium phosphate are one or more selected from hydroxyapatite, fluoroapatite, and tricalcium phosphate. processing method. 5. Claims 1 to 4, wherein the crystal species containing calcium phosphate are phosphate rock or bone charcoal.
A method for treating water containing phosphates according to any of paragraphs.