JPH0512999B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for treating wastewater containing phosphate ions.

(Prior art) In recent years, sewage, industrial water, and various other industrial wastewaters often contain phosphate ions, and these phosphate ions have a high nutrient value in closed water bodies such as lakes, marshes, and inner bays. It has become a problem as a causative agent.

In addition, in sewage and industrial water, the concentration of phosphate ions in water is low, but the amount of water is large, which poses a problem, while industrial wastewater, which has a small amount of water, may contain phosphate ions in high concentrations, which poses a problem for the environment. The impact is significant.

Conventionally, the mainstream method for removing phosphate ions from wastewater is chemical coagulation using metal salts, which can be applied not only to wastewater containing low concentrations of phosphate ions but also to wastewater with high concentrations. is now possible. In this method, phosphate ions are precipitated and removed as sparingly soluble metal salts, but it is necessary to add more metal salts than the amount calculated according to stoichiometry, and the amount of metal salts in wastewater is Because of the side reaction in which the added metal salt is hydrolyzed by the alkali present, it is necessary to further add the metal salt, resulting in problems such as high cost. In addition, a large amount of sludge with poor waterproof properties is generated, and its treatment and disposal have become problems.

Other methods include, for example,
By adding calcium ions from the outside as described in Publication No. 225692 and Japanese Patent Application Laid-Open No. 60-61092, phosphate ions contained in water are converted into calcium phosphate crystals such as hydroxyapatite and deposited on the surface of the seed crystal. It is known that it can be removed by

The control method and control device for the contact crystallization dephosphorization method described in JP-A No. 60-225692 are
A plurality of operating curves of calcium ion concentration that cause an optimal crystallization reaction with respect to the phosphate ion concentration of wastewater at PH value are set at a plurality of different PH values. Then, one of the operating curves is adopted according to the phosphate ion concentration, and a calcium solution is injected into the phosphate ion-containing wastewater, and the pH of the alkaline solution is adjusted so that the required calcium ion concentration is obtained. Inject. Furthermore, a configuration is adopted in which hydroxyapatite crystals are introduced, stirred, and removed by depositing on the crystal surface.

In addition, the dephosphorization method described in JP-A No. 60-61092 uses a reaction tank such as a fixed bed to collect water to be treated containing phosphate and crystal seeds containing calcium phosphate compounds such as bone char and phosphate rock. is brought into contact with calcium ions at a pH of 6 or higher and removed as a crystalline apatite layer on the surface of the crystal seeds, the precipitated surface layer of the crystal seeds is peeled off, reactivated, and reused. A configuration has been adopted to do so.

(Problems to be Solved by the Invention) However, the control method and control device for the contact crystallization dephosphorization method described in the above-mentioned Japanese Patent Application Laid-open No. Sho 60-225692 does not solve the problem in the metastable region in the relationship between the phosphate ion concentration and the PH value. After pre-treatment to adjust the pH value and calcium ion concentration so that In this case, an unstable region occurs and flocculated sludge is generated, and the crystallization reaction that crystallizes phosphate ions on the surface of the crystallization material does not occur, making it difficult to separate the flocculated sludge and treated water, which increases the processing cost of flocculated sludge. As this increases, the activity of the crystallizing material decreases, causing a problem of inhibiting the crystallization reaction.

In addition, the dephosphorization method described in JP-A No. 60-61092 also involves adjusting the hydroxyapatite metastable region at a pH of 6 or higher and in the presence of calcium ions. Dephosphorization is performed by bringing treated water into contact with crystal seeds containing calcium phosphate compounds, and if the phosphate ion concentration of the treated water is high, it will become an unstable region and cause flocculated sludge. Separation of the flocculated sludge and treated water becomes difficult, which increases the cost of treating the flocculated sludge, and also reduces the activity of the crystallization material, which poses a problem of inhibiting the crystallization reaction.

The present invention has been made in view of the above-mentioned problems, and it overcomes the drawbacks of the flocculation method, which generates a large amount of sludge with poor dewatering properties, and also overcomes the drawbacks of the flocculation method, which generates a large amount of sludge with poor dewatering properties, as well as the low concentration of phosphorus-containing wastewater and low phosphorus load of the conventional crystallization method. It can be applied to a wide range of phosphorus-containing wastewater from medium to high concentrations, and it also makes it possible to greatly increase the amount of phosphate ions loaded, and it does not reduce efficiency even after long-term operation. It is an object of the present invention to provide a method for treating wastewater containing phosphate ions that does not generate phosphoric acid ions.

(Means for Solving the Problems) The method for treating wastewater containing phosphate ions of the present invention involves suspending hydroxyapatite microcrystals as a crystallization material in water in a stirring tank, and then suspending hydroxyapatite microcrystals containing phosphate ions. The water to be treated is passed through the stirring tank, and the pH in the stirring tank is adjusted to 6.0 or more, and calcium ions are added so that the molar ratio of phosphorus and calcium is 40 mg/or more than the 3:5 molar ratio. The phosphate ions are crystallized as apatite in the crystallization material, and the phosphate ions are removed from the water to be treated. This method attempts to rapidly remove a high load of phosphate ions by crystallizing phosphate ions and suspending fine crystallization material at a high concentration.

Furthermore, the present invention makes it possible to repeatedly use the crystallization material by separating the treated water from the crystallization material that has crystallized phosphate ions and returning it to the stirring tank. This also eliminates the need for replenishment.

Furthermore, the present invention adds calcium ions to the water to be treated containing phosphate ions in a stirring tank while adjusting the pH to generate and suspend hydroxyapatite microcrystals as a crystallization material, and then phosphate ions. The water to be treated containing
6.0 or more, add calcium ions and stir while adjusting the molar ratio of phosphorus and calcium so that the molar ratio of phosphorus and calcium is 40 mg/or more than 3:5, and phosphate ions are crystallized as apatite in the crystallization material. By removing phosphate ions from the water to be treated, Ca ions are added to the phosphate ions in the water to generate hydroxyapatite microcrystals as a crystallization material, and the crystallization material is added from other sources. The purpose is to start the crystallization reaction without causing any damage.

Furthermore, the present invention utilizes phosphate ions in the water to be treated to generate a crystallizing material by itself, and the crystallizing material in which the phosphate ions are crystallized is separated from the treated water and returned to the stirring tank for use. This aims to completely eliminate the need to supply crystallizing material from other sources.

(Function) The method for treating wastewater containing phosphate ions of the present invention involves suspending hydroxyapatite microcrystals as a crystallization material in water in a stirring tank, and then stirring the water to be treated containing phosphate ions. Water is passed through the tank, the PH in the stirring tank is adjusted to 6.0 or higher, and calcium ions are added to adjust the molar ratio of phosphorus and calcium to 40 mg/or more than 3:5 while stirring. In order to remove phosphate ions from the water to be treated by crystallizing phosphate ions as apatite as a crystallization material, conventional crystallization is not possible because hydroxyapatite as a crystallization material is in the form of microcrystals and suspended in water. Compared to the material filling method, the surface area of the crystallizing material is expanded, the MLSS of the crystallizing material can be reduced, and high concentrations of phosphate ions can be removed by crystallization.

Furthermore, in the present invention, the crystallization material that has been separated from the treated water by crystallizing phosphate ions is directly returned to the stirring tank and used as the crystallization material, so it can be used repeatedly without replenishing the crystallization material. .

Furthermore, the present invention adds calcium ions to the water to be treated containing phosphate ions in a stirring tank while adjusting the pH to generate and suspend hydroxyapatite microcrystals as a crystallization material, and then phosphate ions. The water to be treated containing
6.0 or more, add calcium ions and stir while adjusting the molar ratio of phosphorus and calcium so that the molar ratio of phosphorus and calcium is 40 mg/or more than 3:5, and phosphate ions are crystallized as apatite in the crystallization material. In order to remove phosphate ions from the water to be treated, the phosphate ions contained in the water to be treated are used to generate a crystallization material, and the crystallization reaction can be carried out without adding a separate crystallization material. Moreover, since the crystallization material produced using the water to be treated has microcrystals of 100 microns or less, the crystallization area is expanded and high concentrations of phosphate ions can be removed.

Furthermore, the present invention utilizes the phosphate ions contained in the water to be treated to generate a crystallization material, and the phosphate ions are crystallized in the crystallization material, which is then repeatedly used as the crystallization material. There is no need for separate addition of crystallizer in subsequent runs.

(Example) The configuration of an example of the method for treating wastewater containing phosphate ions of the present invention will be described.

The reaction in which phosphate ions in the water to be treated react with calcium ions to produce hydroxyapatite microcrystals and the reaction in which new apatite is formed by crystallization on the surface of the crystallization material are expressed by the following equation.

5Ca ²⁺ +3PO ₄ ^3- +OH ^- →Ca ₅ (PO ₄ ) ₃ OH...(1) As shown in equation (1), in order to proceed with the reaction that converts phosphate ions in the water to be treated into apatite on the right side, , Ca ion, and OH ion are required, and it can be seen that increasing their concentration is sufficient. In order to obtain a practical reaction rate, in the present invention, the molar ratio of PO ₄ ions and Ca ions is 40 mg/molar rather than 3:5.
In order to increase the amount, preferably 80 mg/or more, and to form crystals, it is necessary to perform the treatment under conditions of pH 6 or higher.

In such crystallization reactions, the surface area of the crystal is an important factor. Therefore, efficiency can be further improved by using a crystallization material with a particle size as small as possible. That is, hydroxyapatite microcrystals with a particle size of 100 μm or less are used as the crystallization material. When such a crystallization material is suspended in water in a stirring tank, or by suspending a crystallization material produced by adding Ca ions to the water to be treated containing PO ₄ ions, the particle size increases. 100μ or less, it is about 1/10 that of the conventional dephosphorization method, and the specific surface area is 100μ or less.
Since the amount of crystallization material is doubled, the amount of crystallization material required is small.
Furthermore, since there is less crystallization material, the stirring power of the stirring tank can also be reduced. Further, since the fine grain crystallization material is suspended in water in a stirring tank and reacted with phosphate ions, even if the water to be treated contains phosphate ions at a high concentration, the water can be passed through and reacted. This is because the crystallization reaction in the stirring tank takes place quickly, and the phosphate ion concentration is very low, almost equal to the phosphate ion concentration in the treated water. It is diluted with treated water in the tank and its concentration drops rapidly. For this reason, calcium phosphate flocs other than apatite are difficult to form.
Moreover, even if such flocs are formed, the solubility of such flocs is generally high, and they will rapidly dissolve under the phosphate ion concentration, Ca ion concentration, and pH in the bath, which are in equilibrium with apatite. Therefore,
PO ₄ - PO ₄ from secondary treated water with a P concentration of about 5mg/
- It is possible to treat a wide range of industrial wastewater with a P concentration of around 1000mg/.

Phosphate ions in the water to be treated crystallize as apatite on the surface of the crystallization material in the stirring tank, and after being removed from the water to be treated, the mixed liquid consisting of the treatment liquid and crystallization material in the tank is transferred to a solid-liquid separation tank. The treated water is separated into treated water and apatite microcrystal slurry. The treated water is discharged and the apatite microcrystal slurry is extracted. Phosphate ions in the water to be treated are recovered as apatite powder, but the apatite microcrystals in the stirring tank are It can be returned to the stirring tank for concentration (MLSS) adjustment. The amount to be returned is adjusted so that the MLSS in the tank is 4,000 mg/or more, preferably 40,000 mg/or more.
The recovered apatite powder can be used again as a crystallization material, and may also be used as fertilizer.

As an operating method when starting the flow of water to be treated, it is necessary to suspend hydroxyapatite microcrystals in the water in the stirring tank, but if the phosphate ion concentration in the water to be treated is low, In order to generate a crystallization material using acid ions, apatite microcrystals cannot be produced unless the conditions are extremely harsh, and the amount of apatite microcrystals produced is small.
Even if the water to be treated is subsequently passed through, the phosphorus removal rate is poor, and it is necessary to pass the water through the process for a fairly long period of time. In such a case, it is necessary to add apatite microcrystals to the water in advance and suspend them in a stirring tank. Apatite crystals include bone char powder,
Phosphite powder, synthetic apatite powder, and other powders containing hydroxyapatite as a main component can be used. In addition, if the phosphate ion concentration in the water to be treated is low, add phosphate ions to the stirring tank using phosphate ion-containing water prepared by dissolving phosphate, and add Ca ions.
Apatite microcrystals may be generated by adjusting the pH.

When apatite microcrystals are generated using phosphate ions in the water to be treated, or when apatite microcrystals are added in advance, apatite microcrystals are then synthesized by the phosphate ions in the water to be treated. Therefore, there is no need to add new apatite microcrystals, and the newly generated apatite microcrystals have sufficient dephosphorization efficiency.

As an operating method when starting water flow, if the phosphate ion concentration in the water to be treated is high, fill the stirring tank with the water to be treated, add Ca, and gradually lower the pH.
As the temperature increases, apatite microcrystals can be generated. Phosphate ion concentration in treated water is PO ₄
-If P is 800mg/or more, the phosphate ions in the initially filled water to be treated will cause the water in the stirring tank to rise.
MLSS can be increased to 4000 mg/or more, but if the concentration is lower than that, the water to be treated is passed through further and the MLSS is
can be increased to 4000mg/or more. In this case, since apatite microcrystals have already formed in the stirring tank, the same operation as normal dephosphorization is performed, but since the MLSS concentration is low, the amount of water to be treated is reduced and the phosphorization It is desirable to lower the loading of acid ions.

The apatite microcrystals generated by phosphate ions in the water to be treated are approximately 50 to 60 μm in size, and when adding apatite microcrystals, it is desirable to use particles with a particle size of 100 μm or less, which reduces the large PO ₄ −P load. Achieving quantity. 0.5 for MLSS4000mg/
Kg/ ^m3 /day, but 50,000mg/day or more
It is possible to take a load of Kg/m ³ /day, which is 25 kg/m 3 /day compared to the conventional method.
It has doubled.

In order to obtain sufficient dephosphorization performance, the Ca ion concentration in the treated water should be 40 mg/or more, preferably 80 mg/or more.

Next, the configuration of an apparatus for carrying out an embodiment of the method for treating wastewater containing phosphate ions will be described based on FIG. 1.

If there is a large amount of suspended solids in the water to be treated, remove the suspended solids by passing the water through a settling tank or sand filter tank in advance. The water to be treated from which suspended solids have been removed is introduced into a stirring tank 2 from a raw water inlet pipe 1 .
Hydroxyapatite microcrystals are present in the water in the stirring tank 2 and are well stirred by the stirrer 3. Calcium is added to the stirring tank 2 from a calcium chloride inflow pipe 4 in accordance with the phosphate ion concentration in the water to be treated. Further, a PH electrode 5 is placed in the stirring tank 2, and alkali is added from an alkali inflow pipe 6 so that the pH in the stirring tank becomes a predetermined value.
By adding calcium and adjusting the pH in this way, phosphate ions in the water to be treated are crystallized into a crystallization material made of hydroxyapatite microcrystals. The mixed liquid consisting of the crystallization material obtained by crystallizing phosphate ions and the treated water in the stirring tank 2 flows through the mixed liquid outflow pipe 7.
The water is introduced into a solid-liquid separation tank 8, where the treated water, crystallization material, and hydroxyapatite microcrystals made of the substance to be crystallized are separated into solid-liquid. The treated water is led out of the system from the treated water outflow pipe 9. Microcrystals consisting of the crystallization material and the substance to be crystallized are drawn out as a slurry from the bottom of the solid-liquid separation tank 8 through the slurry valve feed pipe 10, and introduced into the stirring tank 2 by the slurry pump 11. A part of the slurry consisting of hydroxyapatite microcrystals is transferred to the slurry drawing tube 1.
2 to the outside of the system.

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

4000ml of synthetic apatite MLSS is placed in water (e.g. tap water) in a cylindrical stirring tank with an inner diameter of 14cmφ and a height of 13cm.
mg/, and stirred with a stirrer.
Chemical industrial wastewater was used as the water to be treated.

Next is the water quality.

Water quality to be treated: PH 3.0 PO ₄ -P 200mg/Ca 440mg/Water to be treated is passed through a stirring tank for a retention time of 10 hours.
The pH inside the tank was controlled to 7.0 with Ca(OH) ₂ . The effluent water was flowed into a solid-liquid separation tank, where it was separated into treated water and crystallization material, and the slurry consisting of the crystallization material was returned to the stirring tank. As the crystallization material (MLSS) concentration gradually increased with operation, Experiment 1 was conducted by shortening the residence time and increasing the PO ₄ -P loading amount accordingly.

The results are shown in FIG. in 10 days
Since the MLSS was 49000mg/, the crystallized material was extracted after that. As is clear from Fig. 2, we started with a PO ₄ -P load of 0.5 Kg/m ³ /day,
In the end, the load was increased to 5.7Kg/m ³ /day, but
The PO ₄ -P concentration in the treated water was 10 mg/less or less, and the removal rate was over 95%. The hydroxyapatite generated in particular at 5.7Kg/m ³ /day is approximately 29,000 mg/day when converted to MLSS value, and the MLSS in the tank is replaced every two days, meaning that this loading period lasted for more than a month. This shows that the newly generated hydroxyapatite microcrystals have sufficient dephosphorization performance and there is no risk of a decrease in efficiency. Control PH after 33rd day of operation
When the pH value was increased to 9.0, the treated water PO ₄ -P was 2 mg/, and the effect of increasing the PH value was recognized. Furthermore, Ca
(OH) ₂ was used to control the pH, but since there were sufficient Ca ions in the treated water, the treated water
The average Ca ion concentration was about 280 mg/.

Next, using the same equipment and the same water to be treated as in Experiment 1, 5000 mg of bone char powder was added to the stirring tank and the pH
Experiment 2 was conducted under the same conditions as Experiment 1 except that the control alkali was NaOH and the control pH was 9.0.

The results are shown in Figure 3. MLSS gradually increases as you drive
Since the concentration has increased, the residence time can be shortened and the PO ₄ −
P loading amount was increased. In the end, the load was increased to 4Kg/m ³ /day, but the PO ₄ -P concentration in the treated water was about 20
mg/ showed a removal rate of 90%. Treated water at this time
The Ca concentration was 43 mg/. Ca after 20th day of operation
When 40 mg of ions were added, the treated water PO ₄ -P
was less than 10mg/representing a removal rate of 95%.

Furthermore, a cylindrical stirring tank with an inner diameter of 14 cmφ and a height of 13 cm was filled with the same water to be treated as in Example 1, and the inside of the tank was stirred. Next, the pH in the tank is gradually increased with Ca(OH) ₂ until it reaches 9.0. After that, the water to be treated is passed through a stirring tank for a residence time of 24 hours, and the effluent water is flowed into a solid-liquid separation tank, where it is separated into treated water and hydroxyapatite microcrystals, and a slurry made of hydroxyapatite microcrystals is transferred to the stirring tank. It was sent back to . 4
After a day, the MLSS in the tank became 4200mg/, so
After that, experiment 3 was conducted by dephosphorizing the raw water with a residence time of 10 hours. In addition, control PH9.0
It remains as it is.

The results are shown in FIG. The PO ₄ -P loading amount was initially started at 0.5Kg/m ³ /day, but after 9 days it was 5.5Kg/m 3 /day.
Kg/ ^m3 /day. The PO ₄ -P concentration in the treated water was less than 2 mg/, indicating a removal rate of more than 99%.

From the various experiments described above, it was confirmed that the method of the present invention can be applied to wastewater containing high concentrations of phosphate ions, and that high-load treatment of PO ₄ -P can be performed stably.

(Effects of the Invention) According to the present invention, hydroxyapatite microcrystals as a crystallization material are suspended in water in a stirring tank, and then treated water containing phosphate ions is passed through the stirring tank. The PH in the stirring tank is adjusted to 6.0 or higher, and calcium ions are added so that the molar ratio of phosphorus and calcium is 40 mg/more than 3:5 while stirring, and phosphate ions are added to the crystallization material. In order to remove phosphate ions from the water to be treated by crystallizing hydroxyapatite as apatite, it is more effective than the conventional filling method of crystallizing material because hydroxyapatite as a crystallizing material is microcrystalline and suspended in water. The surface area of the crystallization material is expanded, the MLSS of the crystallization material can be reduced, and high concentrations of phosphate ions can be removed by crystallization.

Furthermore, in the present invention, the crystallization material that has been separated from the treated water by crystallizing phosphate ions is directly returned to the stirring tank and used as the crystallization material, so it can be used repeatedly without replenishing the crystallization material. .

Furthermore, the present invention adds calcium ions to the water to be treated containing phosphate ions in a stirring tank while adjusting the pH to generate and suspend hydroxyapatite microcrystals as a crystallization material, and then Water to be treated containing ions is passed through the stirring tank, and the water inside the stirring tank is
Stir while adjusting the pH to 6.0 or more and adding calcium ions so that the molar ratio of phosphorus and calcium is 40 mg/more than 3:5. Phosphate ions are crystallized as apatite in the crystallization material. In order to remove phosphate ions from the water to be treated, the phosphate ions contained in the water to be treated are used to generate a crystallization material, and the crystallization reaction can be carried out without adding a separate crystallization material. Moreover, since the crystallization material produced using the water to be treated has microcrystals of 100 microns or less, the crystallization area is expanded and a high concentration of phosphate ions can be removed.

Furthermore, the present invention utilizes the phosphate ions contained in the water to be treated to generate a crystallization material, and the phosphate ions are crystallized in the crystallization material, which is then repeatedly used as the crystallization material. There is no need for separate addition of crystallizer in subsequent runs.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an embodiment of the apparatus used in the method of the present invention, and FIGS. 2 to 4 show PO ₄ -P compared to the number of operating days according to the method of the present invention.
It is a chart showing the removal rate, the amount of crystallization material in the tank, and the amount of PO ₄ -P loaded per day.

Claims (1)

[Scope of Claims] 1. Hydroxyapatite microcrystals as a crystallization material are suspended in water in a stirring tank, and then water to be treated containing phosphate ions is passed through the stirring tank. Stir while adjusting the pH to 6.0 or more and adding calcium ions so that the molar ratio of phosphorus and calcium is 40 mg/more than 3:5. Phosphate ions are crystallized as apatite in the crystallization material. A method for treating wastewater containing phosphate ions, which comprises removing phosphate ions from water to be treated by analysis. 2 Hydroxyapatite microcrystals as a crystallization material are suspended in water in a stirring tank, and then water to be treated containing phosphate ions is passed through the stirring tank to raise the pH in the stirring tank to 6.0 or higher and calcium Add ions and stir while adjusting the molar ratio of phosphorus to calcium so that the molar ratio of phosphorus and calcium is 40 mg/or more than 3:5, crystallize phosphate ions as apatite in the crystallization material, and then solidify. A wastewater containing phosphate ions, characterized in that treated water and a crystallization material in which phosphate ions have been crystallized are separated in a liquid separation tank, and the crystallization material in which phosphate ions have been crystallized is returned to the stirring tank. processing method. 3. The phosphate ion according to claim 1 or 2, wherein the hydroxyapatite microcrystal as the crystallization material is at least one of bone char powder, phosphate rock powder, and synthetic apatite powder. wastewater treatment methods, including: 4 In the water to be treated containing phosphate ions in the stirring tank
Calcium ions are added while adjusting the pH to generate and suspend hydroxyapatite microcrystals as a crystallization material, and then the water to be treated containing phosphate ions is passed through the stirring tank. Crystallize phosphate ions into the crystallization material as apatite by adjusting the pH to 6.0 or higher and adding calcium ions so that the molar ratio of phosphorus and calcium is 40 mg/or more than 3:5. A method for treating wastewater containing phosphate ions, which comprises removing phosphate ions from water to be treated. 5 In the water to be treated containing phosphate ions in the stirring tank
Calcium ions are added while adjusting the pH to generate and suspend hydroxyapatite microcrystals as a crystallization material, and then the water to be treated containing phosphate ions is passed through the stirring tank. Crystallize phosphate ions into the crystallization material as apatite by adjusting the pH to 6.0 or higher and adding calcium ions so that the molar ratio of phosphorus and calcium is 40 mg/or more than 3:5. Next, the treated water is separated from a crystallization material in which phosphate ions have been crystallized in a solid-liquid separation tank, and the crystallization material in which phosphate ions have been crystallized is returned to the stirring tank. A method for treating wastewater containing ions. 6. The wastewater containing phosphate ions according to any one of claims 1 to 5, characterized in that the concentration of hydroxyapatite microcrystals as a crystallization material in the stirring tank is 4000 mg/or more. processing method.