JPH054159B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a material for crystallizing phosphate ions in wastewater, which removes phosphate ions dissolved in wastewater by crystallizing them as calcium phosphate.

(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 seed crystals.

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, for example, as described in JP-A-60-14990. .

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 place of production, so there are problems with different types, such as a stable dephosphorization effect cannot be expected. be.

Therefore, for example, as described in JP-A-58-139784, a carrier made of inexpensive and easily available zeolite or limestone is used as a seed crystal, and the concentration of phosphoric acid or phosphate is from 100 mg/ to several times. Phosphorus is adsorbed and carried on the surface of the carrier by immersing it in an aqueous solution containing 10% by weight. At this time, the pH of the phosphoric acid (salt) aqueous solution is not particularly limited, but is preferably less than 6 in order to improve the adsorption of phosphorus onto the carrier surface.

After the carrier and the aqueous solution are in contact for about 3 to 50 hours, depending on the type, concentration, pH, etc. of the phosphate, the carrier from which the solution has been separated is mixed with an aqueous solution containing lime such as a slaked lime aqueous solution. The contact time is about 1 to 7 days, and the phosphorus supported on the surface of the carrier reacts with calcium hydroxide to form calcium phosphate crystals on the surface of the carrier.

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. Due to problems such as adhesion,
It is necessary to separate the carrier and the phosphorus-containing aqueous solution.
Further, the aqueous solution containing lime is desirably adjusted to a solution containing calcium hydroxide in an amount of 4 times or more by weight relative to the amount of supported phosphorus.

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.

(Problem to be Solved by the Invention) However, in the dephosphorization agent and dephosphorization method that are seed crystals described in the above-mentioned Japanese Patent Application Laid-open No. 58-139784, after supporting phosphate ions, calcium ions are Calcium phosphate must be supported, which complicates the production of the dephosphorizing agent, makes it impossible to efficiently support calcium phosphate crystals, and has the problem of limiting the reduction in manufacturing costs.

The present invention was made in view of the above-mentioned problems, and allows calcium phosphate with a stable chemical composition to be efficiently and economically supported on an inexpensive and easily available inorganic porous material, thereby achieving efficient and stable dephosphorization. An object of the present invention is to provide a method for producing a phosphate ion crystallization material in wastewater.

(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 that removes phosphate ions in wastewater by crystallizing them as calcium phosphate. An inorganic porous body having pores of of the inorganic porous material to form calcium phosphate crystals in the pores of the inorganic porous material.

(Function) The method for producing a phosphate ion crystallization material in wastewater of the present invention is to prepare an inorganic porous body having a large number of pores containing phosphate ions and calcium ions whose pH value is adjusted to 6 or less. of the aqueous solution.
Gradually raise the PH value to 8.5 or higher over 10 hours,
By gradually generating calcium phosphate in the pores of the inorganic porous material, crystalline calcium phosphate of constant quality can be supported on the inexpensive inorganic porous material, and phosphate ions can be removed through stable crystallization. In addition, by adjusting the pH of the aqueous solution containing phosphate ions and calcium ions, it is possible to support calcium phosphate crystals that are strong, difficult to peel off, and of constant quality on the surface and internal pores of the inorganic porous material, allowing crystallization. It is highly effective and can stably remove phosphate ions in wastewater for a long time by crystallization. moreover,
Calcium phosphate is supported by adjusting the pH in an aqueous solution where phosphate ions and calcium ions coexist, so after supporting phosphate ions, it is possible to carry out one step without having calcium phosphate supported by calcium ions. It is possible to efficiently support calcium phosphate crystals that are strong, hard to peel off, and of constant quality, and also to simplify the manufacturing process and economically manufacture the calcium phosphate crystallization material.

(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.

The inorganic porous body used as a carrier for the phosphate ion crystallization material is preferably a substance that is cheaper and easier to obtain than bone char, phosphate rock, etc. that are generally used as crystallization materials. Further, a material having an internal structure from which the supported calcium phosphate is difficult to peel off is desirable. Specifically, zeolite, perlite, porous glass, lightweight building material scraps such as foamed cement, and inorganic materials such as ceramics can be used as the carrier.

When used as a phosphate ion crystallization material, it is important to support the supported calcium phosphate so that it does not peel off from the carrier. In other words, if a substance in which calcium phosphate is simply attached to the surface of the carrier is used as a phosphate ion crystallization material, the calcium phosphate will peel off from the carrier during the dephosphorization process or during backwashing, resulting in dephosphorization. This is undesirable as it reduces the effectiveness or flows out into the treated water after dephosphorization.

To deal with this, if calcium phosphate is supported not only on the surface of the carrier but also in the internal pores, it will be difficult to peel off, and a stable phosphorus removal effect as a seed crystal can be expected. 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 carrier, which is an inorganic porous material having the above-mentioned conditions, is first mixed with an aqueous solution containing phosphate ions and calcium ions under a pH of 6 or less. make contact with it.

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.

In addition, the contact time between the carrier and the aqueous solution containing phosphate ions and calcium ions varies depending on the phosphate ion concentration and pH of the aqueous solution, but is usually
It may be 10 to 50 hours, preferably 20 to 50 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 way, a carrier made of an inorganic porous material is mixed with an aqueous solution containing phosphate ions and calcium ions and the pH
After contacting under conditions of 6 or less, the pH value of the aqueous solution is gradually raised to 8.5 or more 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 20 to 50 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.

Further, after contacting the inorganic porous carrier with an aqueous solution containing phosphate ions and calcium ions under conditions of pH 6 or less, the PH value of the aqueous solution was gradually raised to 8.5 or higher over 10 hours or more, and the surface of the carrier and In the step of supporting calcium phosphate crystals in the internal pores, if 0.5 to 1.0% of calcium phosphate cannot be supported on the carrier based on the carrier weight in one step, after the step of increasing the PH value is completed, the phosphoric acid An aqueous solution having the same composition as the aqueous solution containing 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, check the PH value of the aqueous solution inside the device.
Try to keep it above 8.5. 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 crystallization material in wastewater will be described based on FIG. 1.

A tank 1 serving as a fluidized bed stores an aqueous solution containing phosphate ions and calcium ions, and a packed bed 2 filled with an inorganic porous material is formed in this aqueous solution, and a PH measuring device 3 is inserted. has been done. Further, a circulation path 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 introduction port.

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

Next, the configuration of an apparatus for carrying out a method for removing phosphate ions from wastewater using the phosphate ion crystallization material obtained in the above example will be explained based on FIG. 2.

A crystallization material layer 8 filled with a phosphate ion crystallization material in which calcium phosphate crystals are supported on an inorganic porous material is formed in the crystallization tank 7 serving as a fixed bed. The treated water introduction channel 9 is connected,
A treated water outlet pipe 10 is led out from the bottom of the crystallization tank 7 . Furthermore, in the middle of the treated water introduction path 9,
The PH adjustment tank 11 is inserted, and the PH adjustment tank 11 has a
While the measuring device 12 and the stirrer 14 are inserted,
A slaked lime supply pipe 13 is connected.

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 treated water from which the phosphate ions have been removed is derived.

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,
An acrylic column with a length of 200 cm was constructed using zeolite as the inorganic porous material.
Fill with 500ml. Then, the phosphorus concentration in this column is
Fill with synthetic water adjusted to 200mg/, calcium concentration 500mg/, and pH 5.0 to fluidize the filling. After leaving this condition for 24 hours, the pH inside the column
The value was gradually increased to 9.0 over 24 hours by addition of NaOH. In this way, zeolite
A phosphate ion crystallization material was formed by supporting 0.8% calcium phosphate.

Next, an acrylic column with a diameter of 2 cm and a length of 100 cm was used as the fixed bed crystallization tank 7 shown in FIG.
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.
An experiment (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, 0.23mg/, water flow
At the time of BV3600/crystallization material, it was 0.25mg/+.

Further, in the same manner as in Experiment 1 above, pearlite was made to support crystals of calcium phosphate to obtain a phosphate ion crystallization material. The amount of calcium phosphate supported is
It was 0.7%.

Experiment 2 was conducted by passing simulated secondary treated sewage water through this phosphate ion crystallization material in the same manner as in Experiment 1.

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, 0.28mg/, water flow
At the time of BV3600/crystallization material, it was 0.25 mg/.

Furthermore, as in Experiment 1, calcium phosphate crystals were supported on the filter sand, and using a phosphate ion crystallizer with a supported amount of 0.8%, simulated secondary treated sewage water was passed through in the same manner as in Experiment 1. , Experiment 3 was conducted.

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/.

Next, fill an acrylic column with a diameter of 8 cm and a length of 200 cm with 500 ml of zeolite. In this column,
The synthetic water prepared in Experiment 1 was adjusted to pH 8 with NaOH, then filled with water and fluidized. After continuing this state for 24 hours, the pH value in the column was gradually increased to 9 over 24 hours. In this way, zeolite is loaded with 0.5% calcium phosphate crystals,
A phosphate ion crystallization material was obtained.

Experiment 4 was conducted by passing simulated secondary treated sewage water through this phosphate ion crystallization material in the same manner as in Experiment 1.

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, 1.08mg/, water flow
At the time of BV3600/crystallization material, it was 0.92 mg/.

From the above various experiments, we have found that a phosphate ion crystallization material in which calcium phosphate crystals are gradually formed and supported on a carrier made of an inorganic porous material such as perlite or natural zeolite by controlling the pH.
It was recognized that it has excellent dephosphorization ability.

According to the above example, an inexpensive and easily available inorganic porous body having a large number of pores is immersed in an aqueous solution containing phosphate ions and calcium ions whose pH value is adjusted to 6 or less. By gradually raising the PH value of the mineral to 8.5 or higher over 10 hours and gradually generating calcium phosphate in the pores of the inorganic porous material, we can eliminate the need for expensive materials such as bone char or phosphate rock. An inexpensive inorganic porous body can be used. Then, by supporting crystalline calcium phosphate of constant quality on this inorganic porous body, phosphate ions can be removed by stable crystallization. In addition, an inorganic porous material is immersed in an aqueous solution containing phosphate ions and calcium ions, the pH is adjusted, and calcium phosphate crystals that are strong, hard to peel off, and of constant quality are formed on the surface and internal pores of the inorganic porous material. , 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, the inorganic porous material 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 supporting calcium phosphate, it is possible to efficiently support calcium phosphate crystals that are strong, hard to peel off, and have a constant quality in a single process, and the manufacturing process can be simplified, making it possible to economically manufacture calcium phosphate crystallization material. can.

(Effects of the Invention) According to the method for producing a phosphate ion crystallization material in wastewater of the present invention, an inorganic porous body having a large number of pores is mixed with phosphate ions and calcium whose pH value is adjusted to 6 or less. immersed in an aqueous solution containing ions,
By gradually raising the pH value of the aqueous solution to 8.5 or higher over 10 hours and gradually generating calcium phosphate in the pores of the inorganic porous material, crystalline calcium phosphate of constant quality is supported on the inexpensive inorganic porous material. Therefore, phosphate ions can be removed through stable crystallization. In addition, by adjusting the pH of the aqueous solution containing phosphate ions and calcium ions, it is possible to support calcium phosphate crystals that are strong, difficult to peel off, and of constant quality on the surface and internal pores of the inorganic porous material, allowing crystallization. It is highly effective and can stably remove phosphate ions in wastewater for a long time by crystallization. Furthermore, since calcium phosphate is supported by adjusting the pH in an aqueous solution where phosphate ions and calcium ions coexist, after supporting phosphate ions, the calcium phosphate is not supported by calcium ions. 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.

[Brief explanation of the drawing]

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)

[Claims] 1. In a phosphate ion crystallization material for removing phosphate ions in wastewater by crystallizing them as calcium phosphate,
Immerse in an aqueous solution containing phosphate ions and calcium ions prepared as follows, and
Gradually raise the PH value to 8.5 or higher over 10 hours,
A method for producing a material for crystallizing phosphate ions in wastewater, characterized in that calcium phosphate crystals are formed in the pores of the inorganic porous body.