JPH0432714B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a dephosphorization method, and particularly to a dephosphorization method in which a dephosphorization agent is efficiently reactivated in a crystallization dephosphorization method.

[Background Art] In recent years, the progress of eutrophication has become a major problem in closed water bodies such as lakes and inner bays. Phosphate present in water has been highlighted as one of the causes of this eutrophication, and its removal has been raised as an urgent issue. Phosphates that cause eutrophication are contained in tap water, sewage, industrial water, factory wastewater, boiler water, etc., and include inorganic phosphates such as orthophosphates and condensed phosphates, and organic It exists in the form of phosphate.

As a method to remove such phosphates, water containing phosphates is treated in the presence of calcium ions,
A method (crystallization dephosphorization method) has been proposed that involves contacting crystal seeds (dephosphorization agent) containing calcium phosphate such as phosphate rock (Dissertation Abstracts
International, Vol.33, No.12, part I, 5878
-page B, etc.). This method removes phosphate ions contained in water by converting them into calcium phosphate, such as hydroxylapatite, and crystallizing them into crystal seeds. , which can remove phosphorus with high processing efficiency without generating sludge, has attracted particular attention in recent years.

However, when this method is applied to the removal of phosphorus from wastewater containing trace amounts of organic matter and operated for a long period of time, a phenomenon occurs in which the dephosphorization performance gradually decreases. Conventional methods for reactivating dephosphorizing agents include a method of treating with an acidic solution, a method of treating with a lime solution, and the like. However, the method of treatment with an acidic solution has the disadvantage that water containing high concentration of phosphorus is discharged during the activation treatment. On the other hand, in the method of treatment with lime solution, there is no discharge of phosphorus-containing water as seen in the case of treatment with acidic solution, but it is not always satisfactory due to the difference in the cause of deterioration of the dephosphorization performance of the dephosphorization agent. There is a problem that the desired reactivation treatment effect cannot be achieved.

As a result of multifaceted investigation into the causes of dephosphorization of dephosphorization agents, the present inventors confirmed a phenomenon in which chromaticity components adhere to the surface of dephosphorization agents during the process of crystallization dephosphorization treatment. Additionally, as the amount of attached chromaticity component increases, the dephosphorization performance of the dephosphorization agent decreases, and the dephosphorization agent with decreased dephosphorization performance is significantly colored compared to the state before use. was confirmed. However,
In this way, especially when the dephosphorization performance deteriorates due to the adhesion of chromaticity components to the dephosphorizing agent, the reactivation treatment methods that have been proposed to date do not necessarily provide a satisfactory reactivation treatment effect. Nakatsuta.

[Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and its object is to provide a dephosphorization method that can efficiently reactivate a dephosphorization agent.

[Structure of the Invention] In order to achieve this object, the dephosphorization method of the present invention involves contact treatment of a dephosphorizing agent colored by adhesion of chromaticity components with a solution containing phosphate ions or carbonate ions. The chromaticity component is extracted by contacting water containing phosphate and chromaticity component with crystal seeds containing calcium phosphate at a pH of 6 or above in the presence of calcium ions to extract the phosphate in the water. In the dephosphorization method for removing 2
Abstract: A dephosphorization method characterized by bringing a crystal seed to which a chromaticity component of a degree or higher has been attached into contact with a solution containing phosphate ions or carbonate ions to remove the chromaticity component from the crystal seed and reactivate it. That is.

In other words, if the raw water contains chromaticity components (chromaticity components are present in most raw waters such as sewage),
The crystal seeds, which are dephosphorizing agents, ion-exchange their own phosphate ions with the pigment (anion charge) in the raw water. If the amount of ion exchange is less than a predetermined amount, there is no significant effect, and the conventional process is sufficient to reactivate the crystal seeds, but if the amount of ion exchange exceeds a predetermined amount, the effective area becomes and the dephosphorization performance deteriorates significantly. The present inventors found that in the case of crystal seeds contaminated with a large amount of pigment, when the pigment is removed using a specific extractant,
The dye is removed from the active site where the dye was adsorbed, and by ion exchange with phosphate ions and bicarbonate ions, it restores its activity as a dephosphorizing agent and no post-treatment process is required. This heading led to the present invention.

In the present invention, the chromaticity component refers to a substance that, when dissolved or present in colloidal form in water, causes the water to appear light yellow to yellowish brown. Examples of methods for measuring chromaticity include:
There is a method.

The color that appears when a color standard solution (1 mg of chloroplatinic acid and 0.5 mg of cobalt chloride) is added to 1 part of water is 1.
degree. Prepare a series of color standard solutions of 1 to 20 degrees in a colorimetric tube. Pour the test solution, which has been filtered or centrifuged to remove turbidity, into a colorimetric tube, and visually determine the color standard solution to which the test water corresponds. Then, the chromaticity is calculated using the following formula. (JIS K0101 and Water Supply Test Methods, Ministry of Health, Labor and Welfare, Environmental Sanitation Bureau, Water Supply Environment Department) [Chromaticity] = [Applicable chromaticity standard solution (degrees)] x 100 [Sample (ml)] / In the above, identification is used instead of visual inspection. Chromaticity is determined by irradiating light of the same wavelength and measuring its absorbance.

The present invention will be explained in more detail below.

The raw water to be treated in the present invention is water containing color components such as phosphates and organic substances, and includes secondary treated water such as sewage, human waste, and factory wastewater.

In addition, crystal seeds that are dephosphorizing agents can be artificially added to phosphate rock, bone charcoal, or other surfaces (for example,
58-183970, 58-187868, etc.), etc., in which calcium phosphate crystals are precipitated and supported.

Such raw water is placed in the presence of calcium ions.
Crystallization is carried out by contacting with a dephosphorizing agent of crystalline species containing calcium phosphate at a pH of 6 or higher. The reaction that occurs at this time varies depending on the reaction conditions, but is usually expressed by the following formula.

5Ca ²⁺ +7OH ^- +3H ₂ PO ₄ ^- →Ca ₅ (OH) (PO ₄ ) ₃ +6H ₂ O...(1) To efficiently remove phosphate from water containing phosphate (1) It is necessary for the reaction in the formula to proceed to the right, and for this purpose, it is necessary to add a calcium agent or an alkaline agent as necessary to make calcium ions and hydroxide ions present. If the amount of these ions becomes too large, fine precipitates may be formed in places other than the dephosphorizing agent, or calcium carbonate precipitates may be formed, so use calcium agents and alkaline agents to the extent that these do not occur. It is preferable to add That is, the amounts of calcium ions and hydroxyl ions are set in a range in which hydroxyapatite is produced at a concentration higher than the solubility of the hydroxyapatite produced in equation (1) and lower than the supersolubility (i.e., a concentration in the metastable range). preferable. Here, supersolubility is the concentration at which crystals begin to precipitate when no crystal seeds are present in the reaction system.

In order to keep the amounts of calcium ions and hydroxide ions within the above ranges, a calcium agent and/or an alkaline agent is added to the phosphate-containing water as necessary. Suitable amounts of calcium and alkaline agents to be added can be determined in advance through simple experiments, but if the phosphate content in the raw water is 50 mg/or less, the calcium ion content is 10 to 200 mg/, and the pH is approximately 6 to 12. .

Calcium agents used in this invention include:
Calcium hydroxide, calcium chloride, etc. Alkaline agents include sodium hydroxide, potassium hydroxide,
Examples include calcium hydroxide.

The contact between the water containing phosphate and the dephosphorizing agent is preferably carried out by a packed bed water flow system, and in the case of a fixed bed,
In the case of a mesh or fluidized bed, it is filled with a dephosphorizing agent having a particle size of 36 to 300 mesh, and water is passed upwardly or downwardly at a flow rate of SV1 to 20 hr ^-1 to precipitate hydroxyapatite crystals. In the case of upward flow, suspended matter can be captured in the large particle size portion of the lower layer, and crystallization can be performed in the small particle size portion of the upper layer with high activity. Similarly, when water is passed in a downward flow, a filter medium with a smaller specific gravity and larger particle size than the dephosphorizing agent is stacked on top of the dephosphorizing agent packed layer to avoid adhesion of suspended matter to the surface of the dephosphorizing agent. However, it is desirable to remove suspended solids using this filter medium. If the surface of the dephosphorizing agent becomes contaminated or clogged during water flow, backwashing is performed periodically using upward flow to spread out the dephosphorizing agent and remove impurities attached to the surface. It is desirable to do so. Water flow conditions during backwashing include a flow rate of about 20 to 80 m/hr, and a backwashing time of about 5 to 60 minutes.

When crystallization is performed as described above, mainly (1)
According to the formula, hydroxyapatite with low solubility is generated, which crystallizes on the surface of the dephosphorizing agent, and the phosphoric acid concentration in the treated water becomes low.

In such a dephosphorization treatment, if a chromaticity component is attached to the crystal seeds of the dephosphorization agent, reactivation is performed according to the present invention.

The dephosphorization agent to be subjected to the reactivation treatment has a chromaticity component of 2 degrees or more per gram of crystal seed attached. When the chromaticity component is less than 2 degrees, the dephosphorization performance is not so adversely affected, but when it is 2 degrees or more, a phenomenon of activity reduction is observed.

In the present invention, the crystal seeds to which the chromaticity components are attached are brought into contact with a solution containing phosphate ions or carbonate ions. Specific examples of the solution containing phosphate ions or carbonate ions include a sodium dihydrogen phosphate aqueous solution, a sodium hydrogen carbonate aqueous solution, and the like.

These solutions preferably have a pH of 4 or higher, particularly a pH of 4 to 9. In the method of the present invention, a dephosphorizing agent is brought into contact with a solution containing phosphate ions or carbonate ions, and the chromatic components attached to the surface of the dephosphorizing agent are extracted into the solution, removed, and activated. Although the method is
Extraction of chromaticity components is more effective under high pH conditions, and under the same pH conditions, higher phosphate ion or carbonate ion concentrations are more effective. especially,
A method of contact treatment with an aqueous solution containing phosphate ions under conditions of pH 7 or higher is the most efficient method for extracting and removing chromatic components, and also has a large reactivation effect.

In such reactivation treatment of the present invention,
Prior to this treatment, the dephosphorizing agent may be subjected to a heat treatment, or after the reactivation treatment, a water washing treatment step may be provided as necessary.

The dephosphorizing agent with chromaticity components attached to it is heated in advance and then contacted with a solution containing phosphate ions or carbonate ions to extract and remove the chromaticity components attached to the surface of the dephosphorizing agent into the liquid. If so, the heating temperature is
The temperature is preferably 100 to 650°C. Heating temperature is 650
If the temperature exceeds .degree. C., a portion of the surface of the dephosphorizing agent may melt and the surface area may decrease, which is not preferable.

In the present invention, by performing the heat treatment in this manner, the extraction efficiency of the chromaticity component in the subsequent extraction step of the reactivation treatment is significantly promoted.

In addition, in the above treatment, prior to the dephosphorization operation, the raw water is pretreated, the treated water is subjected to post treatment, or other treatments are used together with the dephosphorization treatment, or chemicals are added. is also possible.

[Examples of the Invention] The present invention will be explained in more detail below using experimental examples, working examples, and comparative examples, but the present invention is not limited to the following examples unless the gist thereof is exceeded.

Experimental examples will be explained first, and then examples and comparative examples will be explained.

Experimental Example 1 After air-drying a dephosphorizing agent that had been used for about two years to remove phosphorus from biologically treated domestic wastewater containing pigments and phosphorus (1 to 2 mg/) (weight 10 g after air-drying), the PH
The phosphorus concentration was adjusted to 100mg/
The mixture was stirred in 250 ml of NaH ₂ PO ₄ aqueous solution for 3 hours.
After 3 hours, the supernatant was filtered through a 0.22 μm Millipore filter, and the chromaticity of the filtrate was determined by measuring the absorbance at 450 nm. of the extract (NaH ₂ PO ₄ aqueous solution)
Figure 1 shows the relationship between pH and chromaticity of the filtrate.

The method for measuring chromaticity is as follows.

First, take 2.49 g of potassium chloroplatinate, 2.00 g of cobalt chloride hexahydrate, and 200 ml of hydrochloric acid, add water to dissolve them, put them in a 1000 ml flask, and add water up to the marked line to prepare a color standard stock solution. did.

From this chromaticity standard stock solution, prepare a series of chromaticity standard solutions of 1 to 20 degrees, place each of these in a 50 mm cell, and
The absorbance was measured at 450 nm, and a calibration curve was prepared in advance.

Next, take the test water (filtrate) into a 50 mm cell and find the wavelength
The absorbance was measured at 450 nm, and the chromaticity was determined from the above calibration curve prepared in advance.

From FIG. 1, it is recognized that the amount of extracted chromaticity components tends to increase as the pH of the extract is higher.

Experimental Example 2 Instead of the NaH ₂ PO ₄ aqueous solution in Experimental Example 1, the calcium carbonate concentration was adjusted to 100 mg/
Experimental example 1 except that 250 ml of NaH ₂ PO ₄ aqueous solution was used.
An experiment for extracting chromaticity components was conducted under the same conditions. The results are shown in Figure 1.

From FIG. 1, it can be seen that the amount of extracted chromaticity components tends to increase as the pH increases, similar to the case when an aqueous NaH ₂ PO ₄ solution is used.

Experimental Example 3 The phosphorus concentration of the NaH ₂ PO ₄ aqueous solution of Experimental Example 1 was set to 100.
A chromaticity component extraction experiment was carried out under the same conditions as in Experimental Example 1, except that the amount was varied between ~8000 mg/- and the pH was 4.3-4.9. FIG. 2 shows the relationship between the phosphorus concentration of the extract and the chromaticity of the filtrate.

From FIG. 2, it can be seen that the higher the phosphorus concentration of the extract, the greater the amount of chromaticity component extracted.

Example 1 The same dephosphorizing agent as that used in Experimental Example 1 (used for about 2 years to remove phosphorus from biologically treated domestic wastewater containing pigment and 1 to 2 mg of phosphorus)
150 ml was packed into an acrylic column with an inner diameter of 30 mm and a length of 500 mm. Next, phosphorus concentration 1000mg/, PH9
NaH ₂ PO ₄ aqueous solution 1 adjusted to 1 was circulated through the packed bed of the dephosphorizing agent at a flow rate of 3/hr for 8 hours.

Subsequently, the packed bed of the dephosphorizing agent was washed with about 1 ml of tap water to complete the reactivation process.

Phosphorus concentration 2mg/, total alkalinity approximately 100mg/
At the inlet of the column filled with the reactivated dephosphorizing agent, aqueous solutions of calcium chloride and sodium hydroxide were added to the synthetic water adjusted to a concentration of about 45 mg/pH and a pH of 8.7. ~9.0
After adjusting to
Water was passed at a flow rate of hr. The average value of the phosphorus concentration in the treated water during 10 days of continuous water flow treatment was 0.30 mg/.

Comparative Example 1 Synthetic water was dephosphorized under the same conditions as in Example 1 except that the reactivation treatment was not performed. As a result, the average value of the phosphorus concentration in the treated water during 10 days of continuous water flow treatment was 0.92 mg/.

Comparative Example 2 In Example 1, instead of NaH ₂ PO ₄ aqueous solution
The treatment was carried out in the same manner except that NaOH aqueous solution 1 adjusted to pH 9 was used, and then the synthetic water was similarly dephosphorized. As a result, the average value of the phosphorus concentration in the treated water during 10 days of continuous water flow treatment was 0.90 mg/.

From the results of Comparative Example 2, it was found that simply using the dephosphorizing agent treated water
It can be seen that simply increasing the pH does not produce much of a reactivation effect.

Example 2 The same dephosphorizing agent as that used in Experimental Example 1 (used for about 2 years to remove phosphorus from biologically treated domestic wastewater containing dye and 1 to 2 mg of phosphorus)
was divided into two parts, one was air-dried and the other was heat-treated in a dryer at 105°C for 24 hours. Next, 10g of each was weighed and adjusted to a phosphorus concentration of 1000mg/PH9.
Pour into NaH ₂ PO ₄ aqueous solution and stir with a stirrer.
Reactivation treatments were carried out with various treatment times ranging from 1 to 24 hours.

After the treatment, a filtrate was obtained from the supernatant in the same manner as in Experimental Example 1, and the absorbance of the filtrate was measured. FIG. 3 shows the relationship between treatment time and chromaticity of the filtrate.

The dephosphorizing agent that had been subjected to the reactivation treatment after the heat treatment was packed into a column in the same manner as in Example 1, and the synthetic water was dephosphorized. As a result of continuous water flow treatment for 10 days, the average phosphorus concentration in the treated water was 0.15mg/
It was hot.

From Fig. 3 and the results of the above-mentioned water flow treatment, it is clear that by heat-treating the dephosphorizing agent in advance during the reactivation treatment, the chromaticity component can be removed more effectively, and the resulting reactivated dephosphorizing agent can be treated. It is recognized that the performance is further improved.

[Effects of the Invention] As detailed above, the dephosphorization method of the present invention efficiently extracts and removes the chromaticity components that adhere to the surface of the dephosphorizing agent in the crystallization dephosphorization step, It is possible to effectively reactivate a dephosphorizing agent whose performance has been degraded by extremely simple operations, and it is possible to efficiently remove phosphorus from wastewater.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the pH of the treated liquids (extract liquids) obtained in Experimental Examples 1 and 2 and the chromaticity of the filtrate after the extraction process, and Figure 2 is a graph showing the relationship between the PH of the treated liquids (extract liquids) obtained in Experimental Examples 1 and 2 and the chromaticity of the filtrate after the extraction process. A graph showing the relationship between the phosphorus concentration of the liquid (extract liquid) and the chromaticity of the filtrate after the extraction process, and Figure 3 shows the relationship between the treatment time obtained in Example 2 and the chromaticity of the filtrate after the extraction process. It is a graph showing a relationship.

Claims (1)

[Claims] 1. A dephosphorization method in which phosphates in water are removed by contacting water containing phosphates and chromaticity components with crystal seeds containing calcium phosphate at a pH of 6 or higher in the presence of calcium ions. , characterized in that the crystal seeds to which chromaticity components of 2 degrees or more per gram of the crystal seeds are attached are brought into contact with a solution containing phosphate ions or carbonate ions to remove the chromaticity components from the crystal seeds and reactivate them. Dephosphorization method. 2. The dephosphorization method according to claim 1, wherein the crystal seeds are phosphate rock, bone char, or granules on which calcium phosphate crystal seeds are artificially precipitated. 3 PH of solutions containing phosphate ions or carbonate ions
The dephosphorization method according to claim 1 or 2, wherein is 4 to 9.