JPH054158B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method for producing a phosphate ion crystallization material in wastewater, which removes phosphate ions dissolved in wastewater by crystallizing them as calcium phosphate. Regarding.

(Prior Art) In recent years, eutrophication has become even more serious in closed water bodies such as bays within lakes and marshes. in general,
Organic phosphorus compounds and inorganic phosphates exist in various forms in human excreta and detergents, but these are often discharged into sewage and wastewater, and moreover, they are often discharged into sewage and wastewater. It is not sufficiently removed in the treatment process, and most of it remains in the water as inorganic phosphate ions. This phosphate ion is considered to be a contributing factor to eutrophication in closed water bodies.
Conventionally, various methods of phosphorus removal have been considered.

A well-known method for removing phosphorus is a coagulation precipitation method using metal salts or slaked lime.

This coagulation-sedimentation method is a method in which phosphate ions in water are reacted with metal ions or slaked lime to generate poorly soluble salts and solid-liquid separation, but it requires a large amount of added chemicals and generates a large amount of sludge. This resulted in an increase in processing costs.

In recent years, a crystallization dephosphorization method that utilizes the crystallization phenomenon of hydroxyapatite has been developed as a method to eliminate these drawbacks and efficiently remove phosphate ions from water with simple operations.

In this method, by adding calcium ions from the outside, phosphate ions contained in water are removed by forming calcium phosphate crystals such as hydroxyapatite and depositing them on the surface of the seed crystal.

As this seed crystal, that is, a phosphate ion crystallization removal material, a substance containing calcium phosphate, such as bone char or phosphate rock, is generally used.

However, the product cost and acquisition cost of these seed crystals are not cheap, and the chemical composition and physical properties of phosphate rock vary depending on the production area, so there are various problems such as a stable dephosphorization effect cannot be expected. There are also points.

Therefore, for example, Japanese Patent Application No. 59-195478 (Japanese Patent Application No.
61-74695) and Japanese Patent Application Laid-Open No. 58-199090, PH
The crystallization base material is immersed in a 0.01 to 5% phosphoric acid or phosphate solution adjusted to 5.5 or less for 2 to 50 hours, and then dried and heated for stabilization to form a 0.05 to 10% calcium salt solution. Soak for 10 to 100 hours. and,
A large number of active sites of calcium phosphate and its intermediate products are distributed on the surface of the crystallization base material.

In addition, the phosphate ions in the aqueous solution react with lime to produce a large amount of calcium phosphate, which complicates the treatment process and also causes the formation of fine calcium phosphate crystal seeds with weak binding strength that fall off the surface of the carrier during use. Because of problems such as adhesion, it is necessary to first separate the carrier and the phosphorus-containing aqueous solution and then perform a reaction with calcium ions.

Then, the dephosphorization agent obtained in the above operation is filled into a treatment tank, and the water to be treated containing phosphate is flowed into the treatment tank, and while adding a calcium agent and an alkaline agent as appropriate, A configuration is adopted in which phosphate is crystallized as calcium phosphate by calcium phosphate supported on a dephosphorizing agent to dephosphorize.

In addition, for dephosphorization using pumice, the configuration described in, for example, Japanese Patent Application Laid-Open No. 57-91788 has been adopted.

The dephosphorization method described in JP-A No. 57-91788 is inexpensive and easily available, and the main component is aluminum oxide or aluminum hydroxide, which is a weathered pumice mineral that is porous and has a large water capacity. A water solution containing a water-soluble phosphorus compound is brought into contact with the soil granular natural mineral, and the water-soluble phosphorus compound is reacted with aluminum oxide or aluminum hydroxide to produce aluminum phosphate, which reduces the phosphorus content in the water solution. This is a dephosphorization method that captures and stabilizes aluminum in aluminum and removes it.

(Problem to be solved by the invention) However, the above-mentioned Japanese Patent Application No. 59-195478
74695) and JP-A-58-199090, it is necessary to support calcium phosphate with calcium ions after supporting phosphate ions, and it is difficult to produce a phosphate ion crystallization material. However, there are problems in that the process is complicated, that calcium phosphate crystals cannot be supported efficiently, and that the reduction in manufacturing costs is also restricted.

Furthermore, the dephosphorization method described in JP-A-57-91788 has a problem in that the dephosphorization ability per pumice weight is low.

The present invention was made in view of the above-mentioned problems, and it allows calcium phosphate with a stable chemical composition to be efficiently and economically supported on pumice stone, which is inexpensive and easily available. The purpose of the present invention is to provide a method for producing a phosphate ion crystallization material.

(Means for Solving the Problems) The method for producing a phosphate ion crystallization material in wastewater of the present invention is a phosphate ion crystallization material for removing phosphate ions in wastewater by crystallizing them as calcium phosphate. is immersed in an aqueous solution containing phosphate ions and calcium ions whose PH value is adjusted to 6 or less, and the PH value of the aqueous solution is adjusted to 8.5 for 10 hours or more.
By gradually increasing the temperature above, calcium phosphate crystals are provided in the pores of the pumice.

(Function) The method for producing a material for crystallizing phosphate ions in wastewater according to the present invention is easy to obtain and inexpensive, and uses pumice with a large pore radius and pore volume. Carrying crystalline calcium phosphate,
Phosphate ions can be efficiently removed through stable crystallization. In addition, pumice stone is immersed in an aqueous solution containing phosphate ions and calcium ions, and the pH is adjusted to create a strong, hard-to-peel-off quality product on the surface and internal pores of pumice stone, which has a large pore radius and pore volume. Since constant calcium phosphate crystals are generated, the crystallization effect is high and phosphate ions in the water to be treated can be crystallized and removed stably for a long period of time. Furthermore, pumice stone is immersed in an aqueous solution in which phosphate ions and calcium ions coexist by adjusting the pH, and the pH is adjusted to support calcium phosphate. without having to carry
Calcium phosphate crystals that are strong, hard to peel off, and of constant quality can be efficiently supported in one step, and the manufacturing process can be simplified, so that the calcium phosphate crystallization material can be manufactured economically.

(Example) The configuration of an example of the method for producing a phosphate ion crystallization material in wastewater of the present invention will be described.

As the carrier for the phosphate ion crystallization material, it is desirable to use a substance that is cheaper and easier to obtain than bone char, phosphate rock, etc., which are generally used as crystallization materials. Also,
A material having an internal structure that prevents the supported calcium phosphate from peeling off is desirable.

In other words, if calcium phosphate is supported on a non-porous carrier such as sand and used as a phosphate ion crystallization material, the calcium phosphate will be peeled off from the carrier during the dephosphorization process or during backwashing, and the dephosphorization effect will be reduced. It is undesirable that it may be reduced or leaked into the treated water after dephosphorization.

In addition, even if it is porous and has a large specific surface area and a large pore volume, if the pore radius is small, calcium phosphate will not be sufficiently supported in the internal pores, but will only be supported at the pore entrance or external surface. The amount supported is not so large, and an increase in dephosphorization ability cannot be expected. At the same time, it is difficult to support calcium phosphate, which is solid and difficult to peel off, and the dephosphorization process is difficult, as in the case of using a non-porous carrier such as sand. Calcium phosphate peels off from the carrier during washing or backwashing, reducing the dephosphorization effect or flowing out into the treated water after dephosphorization, which is undesirable.

From the above viewpoint, as a result of exploring various carriers,
It was found that pumice, which belongs to volcanic ejecta, is the most suitable material as a carrier.

Pumice stone is inexpensive and easily available, has a large pore radius, and has a large pore volume, so that calcium phosphate can be easily supported inside the pores. Furthermore, once supported, the supporting force becomes strong, and it is expected that a phosphate ion crystallization material that is difficult to peel off and has an efficient and stable phosphorus removal effect can be formed at a low cost.

When using the phosphate ion crystallization material formed using the pumice selected as a carrier as a dephosphorizing material, it is important to support the supported calcium phosphate so that it does not peel off from the support. In other words, even if pumice is used as a carrier, depending on the supporting process, as mentioned above, calcium phosphate is simply supported on the pumice surface, and pumice is removed during the dephosphorization process or during backwashing. Calcium phosphate peels off from the
This results in undesirable conditions such as a reduction in the dephosphorization effect or leakage into the treated water after dephosphorization.

As a countermeasure to this problem, if calcium phosphate is supported not only on the surface of pumice but also in its internal pores, it will be difficult to peel off, and a stable phosphorus removal effect can be expected as a seed crystal. For this purpose, it is important how calcium hephosphate is supported in the internal pores.

In the method for producing a material for crystallizing phosphate ions in wastewater according to the present invention, a pumice carrier having the above-mentioned conditions is first brought into contact with an aqueous solution containing phosphate ions and calcium ions at a pH of 6 or below. let

The phosphate ion concentration of the aqueous solution is 100mg/
The calcium ion concentration is at least twice the phosphate ion concentration, preferably 2.3% by weight.
Desirably around double that. Furthermore, it is important to control the pH value of the aqueous solution to 6 or less to prevent the formation of calcium phosphate aggregates due to the solubility product.

This is because when aggregates of calcium phosphate are generated in the aqueous solution, the aggregates simply adhere to the surface of the carrier, resulting in a phosphate ion crystallization material with weak supporting power. If dephosphorization is performed, calcium phosphate will peel off from the carrier during the dephosphorization process or during backwashing, resulting in problems such as a reduction in the dephosphorization effect and leakage into the treated water after dephosphorization. It is. Control of PH is also important to prevent this.

Further, the contact time between the carrier and the aqueous solution containing phosphate ions and calcium ions varies depending on the phosphate ion concentration, pH, etc. of the aqueous solution, but may be 10 hours or more, preferably 10 to 30 hours. In this operation, it is important to sufficiently impregnate the internal pores of the carrier with the aqueous solution at a pH of 6 or less, and the longer the contact time, the better.

Note that in contacting the carrier with an aqueous solution containing phosphate ions and calcium ions, controlling the pH of the aqueous solution is an extremely important operating factor, so a contact method that facilitates pH control is required.
Specifically, the contact between the carrier and the aqueous solution containing phosphate ions and calcium ions is carried out using a fluidized bed method,
It is desirable to use a device (hereinafter referred to as the device) similar to a complete mixing type, such as a fixed bed circulation type or a suspension type.

In this manner, the carrier made of pumice is brought into contact with an aqueous solution containing phosphate ions and calcium ions at a pH of 6 or less, and then the PH value of the aqueous solution is gradually increased to 8.5 or higher using NaOH or the like over a period of 10 hours or more. By gradually increasing the pH value, calcium phosphate crystals can be gently deposited on the surface and internal pores of the carrier.

It is better to carry out this process for a long time, but preferably it takes 10 to 30 hours to bring the pH value of the aqueous solution to 8.5.
As mentioned above, preferably, the PH value is gradually increased to 8.5 to 9.0.

If the pH is raised rapidly, aggregates of calcium phosphate will form in the aqueous solution and simply adhere to the surface of the carrier, becoming a phosphate ion crystallization material with weak supporting power.
As mentioned above, this is because calcium phosphate peels off from the carrier during the dephosphorization process or during backwashing, resulting in problems such as a reduction in the dephosphorization effect and leakage into the treated water after dephosphorization. .

For this reason, especially the calcium phosphate crystals generated in the internal pores are difficult to peel off from the carrier and have the effect of making the support on the carrier stronger. It is necessary to create crystals of calcium phosphate.

In this way, the supported calcium phosphate remains on the carrier surface and internal pores without peeling off from the carrier. Further, the amount of calcium phosphate supported on the carrier may be 0.5% or more based on the weight of the carrier. This is not preferable because the larger the supported amount, the better and more stable the dephosphorization ability as a phosphate ion crystallizer, but the manufacturing cost of the phosphate ion crystallizer also increases. Usually, if it is 0.5 to 1.0% based on the weight of the carrier, the dephosphorization ability as a phosphate ion crystallization material can be sufficiently maintained.

In addition, after contacting a pumice support with an aqueous solution containing phosphate ions and calcium ions under conditions of pH 6 or lower, the surface and internal fine particles of the carrier were gradually raised to 8.5 or higher over a period of 10 hours or more. In the process of supporting calcium phosphate crystals in the pores, 0.5~
If 1.0% calcium phosphate cannot be supported on the carrier, after the step of increasing the PH value is completed, an aqueous solution having the same composition as the aqueous solution containing phosphate ions and calcium ions may be passed through the device. In this case, the slower the water flow rate, the better, and usually the SV is preferably 0.3/·carrier·h or less. Also, keep the PH value of the aqueous solution in the device at 8.5 or higher. By adding the above steps, 0.5 to 1.0% of calcium phosphate can be supported on the carrier based on the weight of the carrier.

Next, the configuration of an apparatus for carrying out an embodiment of the method for producing the phosphate ion crystallizing material will be described based on FIG. 1.

An aqueous solution containing phosphate ions and calcium ions is stored in a tank 1 serving as a fluidized bed, and a packed bed 2 filled with pumice is formed in this aqueous solution, and a PH measuring device 3 is inserted. There is. Further, a circulator 5 led out from above the packed bed 2 and equipped with a liquid circulation pump 4 in the middle is introduced into the bottom of the tank 1, and a NaOH supply pipe 6 is connected in front of this inlet.

Then, while circulating the aqueous solution with the circulation pump 4,
By controlling the pH by neutralizing NaOH while checking the pH with the pH measuring device 3, calcium phosphate crystals are generated on the surface of the pumice of the packed bed 2 and in the internal pores.

Next, a second configuration of an apparatus for carrying out a method for removing phosphate ions from wastewater using a phosphate ion crystallization material obtained by one embodiment of the method for producing a phosphate ion crystallization material described above will be described. This will be explained based on the diagram.

A crystallization material layer 8 filled with a phosphate ion crystallization material in which calcium phosphate crystals are supported on pumice is formed in the crystallization tank 7 serving as a fixed bed.
A to-be-treated water introduction channel 9 is connected to the upper part of the crystallization tank 7.
A treated water outlet pipe 10 is led out from the bottom of the tank.
Furthermore, a PH adjustment tank 11 is inserted in the middle of the water introduction path 9, and a PH measuring device 1 is inserted into the PH adjustment tank 11.
2 and the stirrer 14 are inserted thereinto, and the slaked lime supply pipe 13 is connected thereto.

Then, the water to be treated containing phosphate ions to which slaked lime has been added and whose pH has been adjusted is introduced into the crystallization tank 7.
Phosphate ions in the water to be treated are crystallized as calcium phosphate in the crystallization material layer 8, and the water is derived as treated water from which phosphate ions have been removed.

Next, the operation of the above embodiment will be explained.

In the tank 1 which becomes the fluidized bed shown in Fig. 1, a diameter of 8 cm,
Using an acrylic column with a length of 200 cm, fill the column with 500 ml of 0.5-1.0 mm pumice. and,
This column was filled with synthetic water adjusted to a phosphorus concentration of 200 mg/, a calcium concentration of 500 mg/, and a pH of 5.0.
Fluidize the filling. After leaving it in this state for a day and night, the pH value inside the column was adjusted to 12 by adding NaOH.
I gradually raised it to 9.0 over time. In this way, 0.7% of calcium phosphate was supported on pumice to form a phosphate ion crystallization material.

Next, in the crystallization tank 7 which becomes the fixed bed shown in FIG.
Using an acrylic column with a diameter of 2 cm and a length of 100 cm,
This column was filled with 100 ml of the phosphate ion crystallization material formed in the above step, and the simulated secondary treated sewage water with a phosphorus concentration of 2 mg/, a calcium concentration of 30 mg/, and an alkalinity of 100 mg/was adjusted to pH 9.0 with slaked lime. After that, apply SV2 (1/hour) to the column that will become the fixed bed.
Experiment 1 was conducted by passing water through the tube.

As a result, the phosphorus concentration of the treated water is lower than that of the water flowing through B.
V.1200/At the time of crystallization material, 0.20mg/, water flow
At the time of BV3600/crystallization material, it was 0.23 mg/.

Next, as in Experiment 1, calcium phosphate crystals were supported on 0.5 to 1.0 mm of filter sand, and the supported amount was
Experiment 2 was conducted using a 0.8% phosphate ion crystallizer and passing simulated secondary treated sewage water in the same manner as in Experiment 1. However, when increasing the PH value, the PH value was increased to 9.0 over 24 hours.

As a result, the phosphorus concentration of the treated water is lower than that of the water flowing through B.
V.1200/At the time of crystallization material, 0.49mg/, water flow
At the time of BV3600/crystallization material, it was 1.02 mg/.

Furthermore, as in Experiment 1, calcium phosphate crystals were supported on 1.0 mm of activated alumina, and using a phosphate ion crystallization material with a supported amount of 0.7%, Experiment 1
Experiment 3 was conducted by passing simulated secondary treated sewage water in the same manner as in
I went there. However, when increasing the PH value, the PH value was increased to 9.0 over 24 hours.

As a result, the phosphorus concentration of the treated water is lower than that of the water flowing through B.
V.1200/At the time of crystallization material, 1.12mg/, water flow
At the time of BV3600/crystallization material, it was 1.30 mg/.

In addition, 100 ml of pumice of 0.5 to 1.0 mm without supporting calcium phosphate was packed into an acrylic column with a diameter of 2 cm and a length of 100 cm, and simulated secondary treated sewage water was passed through it in the same manner as in Experiment 1. I did 4.

As a result, the phosphorus concentration of the treated water is lower than that of the water flowing through B.
V.1000/at the time of pumice, 1.80mg/, water flow B.
At the time of V.3600/pumice, it was 1.76 mg/.

From the various experiments described above, it has been confirmed that the phosphate ion crystallization material, in which calcium phosphate crystals are gradually formed and supported using pumice as a carrier, has excellent dephosphorization ability. Ta. Furthermore, it has become clear that even if a substance with a high phosphorus adsorption ability is simply used as a carrier, sufficient dephosphorization ability cannot be obtained as a phosphorus removal material.

In the above example, pumice was immersed in a phosphate ion crystallization material in an aqueous solution in which phosphate ions and calcium ions coexist, the pH was adjusted and calcium phosphate was supported, and the surface and pores of the pumice were immersed. The manufacturing method in which calcium phosphate is provided inside the pumice stone has been explained. By immersing pumice stone in an aqueous solution containing calcium phosphate crystals and coexisting with calcium ions, calcium phosphate can be deposited on the surface and internal pores of the pumice stone. Calcium phosphate can also be supported on the surface and in the pores of pumice.

(Effects of the Invention) According to the method for producing a material for crystallizing phosphate ions in wastewater of the present invention, pumice that is easily available, inexpensive, and has a large pore radius and pore volume is used. By supporting crystalline calcium phosphate of constant quality, phosphate ions can be efficiently removed through stable crystallization. In addition, pumice stone is immersed in an aqueous solution containing phosphate ions and calcium ions, and the pH is adjusted to create a strong, hard-to-peel-off quality product on the surface and internal pores of pumice stone, which has a large pore radius and pore volume. Since constant calcium phosphate crystals are generated, the crystallization effect is high and phosphate ions in the water to be treated can be crystallized and removed stably for a long period of time. Furthermore, pumice stone is immersed in an aqueous solution in which phosphate ions and calcium ions coexist by adjusting the pH, and the pH is adjusted to support calcium phosphate. Calcium phosphate crystals that are strong, hard to peel off, and of constant quality can be efficiently supported in one step without being supported, and the manufacturing process can be simplified and the calcium phosphate crystallization material can be economically produced.

[Brief explanation of drawings]

FIG. 1 is a side view showing the configuration of an embodiment of an apparatus used in the method for producing a phosphate ion crystallization material in wastewater according to the present invention. FIG. 2 is a flow sheet showing the configuration of an apparatus for carrying out an embodiment of the method for producing a phosphate ion crystallization material, and FIG. 1 is a flow sheet showing the configuration of an apparatus that implements a method for removing phosphate ions from wastewater using an acid ion crystallization material.

Claims (1)

[Scope of Claims] 1. A phosphate ion crystallizing material for removing phosphate ions in wastewater by crystallizing them as calcium phosphate, which includes pumice, phosphate ions whose pH value is adjusted to 6 or less, and calcium ions. Phosphate ions in wastewater, characterized in that the wastewater is immersed in an aqueous solution containing the pumice, and the pH value of the aqueous solution is gradually raised to 8.5 or more over 10 hours or more, and calcium phosphate crystals are provided in the pores of the pumice. Method for producing crystallization material.