JPH0432715B2 - - 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 that can extremely effectively reactivate crystal seeds 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, which 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 crystallization dephosphorization method is applied to the removal of phosphorus from wastewater containing trace amounts of organic matter and operated over a long period of time, a phenomenon occurs in which the dephosphorization performance of crystal seeds gradually decreases. . Conventional methods of reactivating crystal seeds have been proposed, such as a method of treatment with an acidic solution and a method of treatment with a lime solution. However, the method of treatment with acidic solution
There is a drawback that high concentration phosphorus-containing water is discharged during the activation process. On the other hand, in the method of treatment with lime solution, although there is no discharge of phosphorus-containing water as seen in the case of treatment with acidic solution, depending on the cause of the deterioration of the dephosphorization performance of crystal seeds, it is not always possible to achieve satisfactory reactivation. The effect of chemical treatment may not be achieved.

The present inventors conducted a multifaceted investigation into the cause of the deterioration of the dephosphorization performance of crystal seeds, and as a result, they confirmed a phenomenon in which chromaticity components adhere to the surface of crystal seeds during the process of crystallization dephosphorization treatment. In addition, as the amount of attached chromaticity components increases, the dephosphorization performance of crystal seeds decreases, and crystal seeds with decreased dephosphorization performance may be significantly colored compared to the state before use. confirmed. If the dephosphorization performance deteriorates due to the attachment of chromaticity components to the crystal seeds, the reactivation treatment methods that have been proposed to date may not necessarily produce a satisfactory reactivation effect. Ta.

By the way, when the purpose is to perform advanced phosphorus treatment such as maintaining the phosphorus concentration in the water treated by crystallization dephosphorization at a low concentration of 0.1 g/or less, the treated water from the crystallization dephosphorization treatment as described above may be further treated. An effective method is to remove trace amounts of phosphorus from the treated water flowing out from the crystallization layer by bringing it into contact with a phosphorus adsorbent such as activated alumina.

However, such a method of providing a contact treatment step with a phosphorus adsorbent usually uses an alkaline solution when regenerating the phosphorus adsorbent that has reached equilibrium adsorption, and therefore contains a high concentration of phosphate. There is a problem in that alkaline recycled waste liquid is generated and further treatment of the recycled waste liquid is required.

[Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to be able to efficiently and stably remove phosphorus using crystal seeds and a phosphorus adsorbent, and to An object of the present invention is to provide a dephosphorization method that can reactivate crystal seeds and phosphorus adsorbents extremely effectively and at low cost.

[Structure of the Invention] In order to achieve this object, the present invention regenerates a phosphorus adsorbent whose activity has decreased by adsorbing phosphorus with an alkaline agent, and brings the regenerated waste liquid generated at that time into contact treatment with crystal seeds, This method is designed to regenerate and activate the crystal seeds by extracting and removing the chromaticity components attached to the surface of the crystal seeds. Water containing phosphate and chromaticity components is mixed with calcium phosphate at a pH of 6 or higher in the presence of calcium ions. In the method of removing phosphates in water by contacting with crystal seeds containing crystal seeds and then contacting with a phosphorus adsorbent, the phosphorus adsorbent whose activity has decreased is regenerated by contacting with an alkaline solution, and the phosphorus adsorbent obtained by this regeneration is brought into contact with an alkaline solution. The present invention is characterized in that the dephosphorization method is characterized in that the recycled waste liquid is brought into contact with crystal seeds whose activity has decreased to reactivate the crystal seeds.

In other words, in the crystallization dephosphorization process, if the raw water contains chromatic components (chromatic components are present in most raw waters such as sewage), the crystal seeds are the own phosphate ions and the pigments in the raw water. (anion charge). 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.
When the amount of ion exchange exceeds a predetermined amount, the effective area substantially decreases and the dephosphorization performance deteriorates significantly. The present inventors found that when a crystal seed contaminated with a large amount of dye is removed using a specific extractant, the dye is removed from the active sites that had adsorbed the dye, and the crystal seed is removed. It was found that the activity was restored. As this extractant, a highly alkaline waste liquid containing a high concentration of phosphate, which is generated when a phosphorus adsorbent whose activity has decreased is regenerated with an alkaline agent, can be used. The inventors have discovered that when the attached crystal seeds are treated, the chromaticity components attached to the surface of the crystal seeds are efficiently extracted and the crystal seeds are reactivated, and the present invention has been achieved.

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 color standard solution series of 1 to 20 degrees in a colorimeter 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 Testing Methods, Water Supply Environment Department, Environmental Sanitation Bureau, Ministry of Health and Welfare) [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 phosphates and chromaticity components, and specifically includes sewage,
Examples include secondary treatment of human waste, factory wastewater, etc.

In addition, crystal seeds include calcium phosphate, specifically, phosphate rock, bone charcoal, etc.
Examples include granules in which calcium phosphate crystals are precipitated and supported (by the method disclosed in et al.).

According to the present invention, crystallization is first carried out by bringing raw water into contact with crystal seeds in the presence of calcium ions 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 alkali 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 crystal seeds, or calcium carbonate precipitates may be formed, so add calcium agents and alkaline agents to the extent that these do not occur. It is preferable to do so. That is, it is preferable that the amounts of calcium ions and hydroxyl ions be 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). .

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 raw water if necessary. The suitable addition amount of calcium agent and alkaline agent can be determined in advance by simple experiment, but if the phosphate in raw water is 50mg/or less, calcium ion is
~200mg/, pH is about 6-12. Examples of calcium agents added to raw water include calcium hydroxide, calcium chloride, etc., and examples of alkaline agents include sodium hydroxide, potassium hydroxide, calcium hydroxide, etc.

The contact between the water containing phosphate and the crystal seeds is preferably carried out by a packed bed water flow system, and in the case of a fixed bed, the contact between
Filled with crystal seeds having a particle size of about 35 mesh, or 36 to 300 mesh in the case of a fluidized bed, water is passed upward or downward 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 passing water in a downward flow, in order to avoid adhesion of suspended matter to the crystal seed surface, a filter material with a smaller specific gravity and larger particle size than the crystal seeds is laminated on the crystal seed packed bed. It is desirable to remove suspended solids using this filter material. If the surface of the crystal seeds becomes contaminated or clogged during water flow, periodically backwash the crystal seeds using an upward flow to develop and clean the crystal seeds and remove impurities attached to the surface. is desirable. Water flow conditions during backwashing include a flow rate of approximately 20 to 80 m/hr;
Backwash time is about 5 to 60 minutes.

When crystallization is performed as described above, mainly (1)
According to the formula, hydroxyapatite with low solubility is produced, which crystallizes on the surface of the crystal seeds, and the phosphate concentration in the treated water becomes low.

The treated water obtained by contacting raw water with crystal seeds is
It is then contacted with a phosphorus adsorbent to remove residual phosphate and further reduce the phosphorus concentration.

Examples of the phosphorus adsorbent include aluminum oxide-containing inorganic adsorbents such as activated alumina, magnesia-based adsorbents, and ion exchange resins such as anion exchange resins. These may be used alone or in combination of two or more.

The phosphate-containing water and the phosphorus adsorbent are preferably brought into contact by a packed bed water flow system, and the conditions at this time are preferably the same as the method of contacting with the crystal seeds. However, the pH range is preferably about 5.5 to 6.5, so when contacting with the phosphorus adsorbent, adjust the pH by adding an appropriate acid to the treated water obtained from the crystallization dephosphorization process. is preferred.

In such dephosphorization treatment, if the activity of the crystal seeds or phosphorus adsorbent decreases, reactivation is performed according to the present invention.

The timing of reactivation of crystal seeds and phosphorus agent may be determined based on the phosphorus concentration in the final treated water (treated water obtained by treatment with a phosphorus adsorbent after crystallization dephosphorization), or the crystallization layer A portion of the crystal seeds may be taken out from the sample, the chromaticity of this crystal seed may be measured, and the judgment may be made based on the value.

If the phosphorus concentration in the final treated water exceeds the standard value, or if the chromaticity of the crystal seeds in the crystallization layer exceeds the set value, it is determined that reactivation of the crystal seeds or dephosphorization agent is required. In some cases, the phosphorus adsorbent is first brought into contact with an alkaline solution to effect reactivation.

In the present invention, if the standard phosphorus concentration of the final treated water that requires reactivation treatment is set to a value of 0.1 mg/or more, extremely sophisticated phosphorus removal treatment can be performed. Note that it is advantageous that the crystal seeds that require reactivation treatment have a chromaticity component of 2 or more degrees attached per 1 g of the crystal seeds. When the chromaticity component is less than 2 degrees per gram, the dephosphorization performance is not so adversely affected, but when it is 2 degrees or more per gram, a phenomenon of decreased activity is observed.

The alkaline agent for the alkaline solution used to reactivate the phosphorus adsorbent is not particularly limited, but it is desirable to use one that does not contain calcium ions, such as sodium hydroxide or potassium hydroxide. When reactivation is performed using an alkaline agent containing calcium ions such as calcium hydroxide, the phosphate ions desorbed from the phosphorus adsorbent during the reactivation process react with the calcium ions, forming a precipitate. This is undesirable because it causes

The regenerated waste liquid obtained by reactivation of the phosphorus adsorbent is then contacted with crystal seeds to reactivate it. Since the regenerated wastewater obtained by reactivating the phosphorus adsorbent is high-PH phosphate-containing wastewater, it is suitable for regenerating crystal seeds with chromatic components attached to them. In addition to efficient removal, the crystal seeds themselves are matured and activated due to the high alkalinity of the recycled waste liquid.

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

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 by Examples below, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

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, a sample water (extract liquid described below) was placed in a 50 mm cell, and its absorbance was measured at a wavelength of 450 nm, and the chromaticity was determined from the calibration curve prepared above.

Example 1 Particle size 0.5-1.0 mm used for about 2 years to remove phosphorus from biologically treated domestic wastewater containing 1-2 mg/phosphorus
150 ml of the crystal seeds were packed into an acrylic column with an inner diameter of 30 mm and a length of 500 mm to prepare a dephosphorization tower-1. Separately, 150ml of activated alumina with a particle size of 0.5 to 1.0mm was added to a dephosphorization tower.
It was packed into an acrylic column similar to 1 and used as a dephosphorization tower-2.

Phosphorus concentration 2mg/, total alkalinity approximately 100
Add each aqueous solution of calcium chloride and sodium hydroxide to synthetic water adjusted to pH 8.7 to 9.7.
After that, water was passed through dephosphorization tower-1 at a flow rate of 300 ml/hr. Next, a hydrochloric acid solution was added to the treated water in the dephosphorization tower-1 to adjust the pH to 5.5 to 6.5, and then the treated water was passed through the dephosphorization tower-2 at a flow rate of 300 ml/hr. When the phosphorus concentration of the treated water was measured after continuous water flow treatment for 100 days as described above, the phosphorus concentration of the treated water of dephosphorization tower-1 was 0.8 to 1.0 mg/, and the phosphorus concentration of the treated water of dephosphorization tower-2 was 0.8 to 1.0 mg/. Phosphorus concentration is always 0.1
mg/or less.

When water was continued to flow further, 140 m
From around the 150th day onward, the phosphorus concentration in the treated water from dephosphorization tower-2 began to exceed 0.1 mg/. Then, the water flow was interrupted, and first, the activated alumina filled in the dephosphorization tower-2 was reactivated. Reactivation treatment uses 0.5N sodium hydroxide aqueous solution at 600ml/hr.
This was done by passing water through the tube for 3 hours at a flow rate of . The activated alumina was further washed by running tap water at a flow rate of 600 ml/hr for 24 hours.

Next, 0.5N sodium hydroxide was added to the dephosphorization tower.
1000ml of the 1800ml recycled waste liquid obtained by passing water through 2.
The sample was collected and circulated through dephosphorization tower 1 at a flow rate of 50 ml/min to extract the chromaticity components attached to the surface of the crystal seeds. The chromaticity of the extract after 8 hours of contact treatment was 1410 degrees. This indicates that a chromaticity component of 7.2 degrees was extracted per gram of crystal seeds.

In this way, the reactivation process of dephosphorization tower-1 and dephosphorization tower-2 is completed, and the phosphorus concentration is 2 again.
Synthetic water adjusted to a total alkalinity of approximately 100 mg/hr was passed through the tube at a flow rate of 300 ml/hr. As a result of continuous water flow treatment for 30 days, the phosphorus concentration in the treated water of dephosphorization tower-1 was less than 0.3mg/
The phosphorus concentration of treated water (final treated water) is always 0.1
mg/or less.

The results of this example show that the dephosphorization method of the present invention can extremely effectively reactivate the crystal seeds and phosphorus adsorbent, and can maintain the phosphorus concentration in the treated water at a low concentration. .

[Effects of the Invention] As detailed above, the dephosphorization method of the present invention efficiently removes chromatic components attached to the surface of the crystal seeds by bringing the recycled waste liquid obtained by reactivating the phosphorus adsorbent into contact with the crystal seeds. It extracts and removes well,
It is possible to effectively reactivate crystal seeds whose performance has deteriorated due to adhesion of chromaticity components with an extremely simple operation, and the cost of reactivation treatment can be significantly reduced by reusing recycled waste liquid. . Moreover, the crystal seeds and phosphorus adsorbent enable advanced treatment to efficiently and stably remove phosphorus from wastewater.

Therefore, according to the present invention, phosphorus in wastewater can be removed very economically and industrially advantageously.

Claims (1)

[Claims] 1. Water containing phosphate and chromaticity components is brought into contact with crystal seeds containing calcium phosphate at a pH of 6 or higher in the presence of calcium ions, and then brought into contact with a phosphorus adsorbent to remove phosphorus in the water. In the method of removing acid salts, the phosphorus adsorbent whose activity has decreased is regenerated by contacting it with an alkaline solution, and the regenerated waste liquid obtained by this regeneration is brought into contact with the crystal seeds whose activity has decreased to reactivate the crystal seeds. A dephosphorization method characterized by: 2. The dephosphorization method according to claim 1, wherein the crystal seeds are phosphate rock, bone char, or granules on which calcium phosphate crystals are artificially precipitated. 3. The dephosphorization method according to claim 1 or 2, wherein the phosphorus adsorbent is one or more selected from the group consisting of activated alumina, magnesia-based adsorbent, and ion exchange resin. 4. The crystal seeds with reduced activity are those to which a chromaticity component of 2 or more degrees per gram of crystal seeds is attached, according to any one of claims 1 to 3. Dephosphorization method.