WO2004071970A1

WO2004071970A1 - Method for removing phosphorus in wastewater

Info

Publication number: WO2004071970A1
Application number: PCT/JP2004/001417
Authority: WO
Inventors: Rokurou Aoki; Hajime Inagaki
Original assignee: Nippon Chemical Industrial Co., Ltd; Hipotech Inc
Priority date: 2003-02-12
Filing date: 2004-02-10
Publication date: 2004-08-26
Also published as: KR101031160B1; JP3977757B2; KR20050114619A; CN1741967A; JP2004261640A; CN100335428C

Abstract

A method for removing phosphorus in wastewater, which comprises a first crystallization step of reacting, in a first crystallization vessel, a phosphorus-containing wastewater, calcium chloride and a recycled hydroxyapatite slurry recycled form a precipitation tank and crystallizing, while adjusting the pH of the reaction mixture by the use of a pH-adjusting agent, a second crystallization step of feeding the slurry formed in the first step to a second crystallization vessel, adding calcium chloride to the slurry, to carry out further reaction and crystallization at a pH higher than that in the first crystallization vessel and of 11 or lower, and a step of feeding the slurry formed in the second step to a precipitation tank, carrying out precipitation and separation, discharging a resultant supernatant to the outside of the system as a treated water, and recycling most of the resultant concentrated slurry as the above-mentioned hydroxyapatite slurry. The above method allows the removal of phosphorus in a waste water without the use of a coagulant and also the formation of a hydroxyapatite excellent in filtration and dewatering characteristics from a phosphorus-containing waste water.

Description

Specification

Dephosphorization method of wastewater Technical field

The present invention relates to a method for dephosphorizing wastewater, and more particularly, to a method for dephosphorizing wastewater in which sedimentation and separation of hydroxyapatite from a phosphoric acid-containing wastewater without using a flocculant. . Background art

In recent years, pollution in closed waters such as inland seas and lakes has become a problem, and one of the causes of this pollution is eutrophication by phosphorus compounds. For this reason, various methods for removing phosphorus from the phosphorus-containing wastewater have been conventionally studied. Among them, Japanese Patent Publication No. 56-33082 of Patent Document 1 discloses that after contacting water containing phosphate with a crystal seed containing calcium phosphate in the presence of calcium ions, A method for treating phosphate-containing water in contact with activated alumina is disclosed. Japanese Patent Application Laid-Open No. 58-148384 of Patent Document 2 discloses a method of removing organic solid wastewater in a biological treatment step, and then removing a particulate solid phosphorus containing calcium phosphate. A method for contact treatment is disclosed. In addition, Japanese Patent Application Laid-Open No. 62-382921 of Patent Document 3 discloses that in removing a phosphorus compound contained in wastewater, a cement pretreated with ion phosphate as a dephosphorizing crystallization material is disclosed. A dephosphorization treatment method using is disclosed. Any of these methods is a dephosphorization treatment method by a crystallization separation method by contact.

On the other hand, wastewater from chemical plants that produce or use yellow phosphorus, phosphoric acid, phosphates, and phosphorus compounds, and wastewater from electroless plating plants that use hypophosphorous acid as a reducing agent are, for example, oxidized. To form orthophosphate ions, The wastewater containing orthophosphate ions will be treated. In this example, the concentration of phosphoric acid in the water to be treated is as high as 300 to 30,000 ppm. Before contacting with a packed bed or fluidized bed, add a calcium agent to the stock solution or adjust the pH value to an alkaline side. In this case, fine hydroxyapatite crystals are generated, and the solution becomes cloudy like milk, and there is a problem that phosphate ions cannot be removed effectively.

For wastewater treatment containing such phosphate in high concentrations, such as aluminum sulfate _{_{[A 1 2 (S0 4)}} 3] and ferric chloride (FeCl ₃₎ is used, insoluble aluminum phosphate two © beam of鉄 The method of removing iron phosphate from wastewater is adopted. At that time, there is an optimal pH value, and the pH is adjusted and the chemicals are mixed before coagulation and sedimentation is performed in the settling basin. To remove phosphoric acid from milky milky turbid liquid using a calcium-containing particulate solid phosphorus remover, a method of adding a polymer flocculant and performing coagulation precipitation must be adopted. .

(Patent Document 1)

JP-A-56-33082 (Claims 1 to 3)

(Patent Document 2)

JP-A-58-143884 (Claim 1)

(Patent Document 3)

JP-A-62-38291 (Claim 1)

(Patent Document 4)

Special issue 2001-7095 No. 1 (Claim 1)

However, in the method of Ru using a sulfate _{_{_{[A1 2 (S0 4) 3}}} ] and ferric chloride (FeCl _3), etc. sulfuric acid band other than crystallization out agent, it is also used as a flocculant, phosphorus Requires a large amount of chemicals more than acid equivalent, processing cost There is a problem that is high. In addition, a large amount of sludge is generated in proportion to the chemical injection amount. However, since this sludge is sticky, its sedimentation, concentration and dehydration properties are extremely poor, and processing costs such as drying costs are reduced. There is a problem of bulkiness. Further, JP-A-2001-70951 of Patent Document 4 discloses that a calcium compound and sludge are mixed in a sludge preparation tank, for example, for 5 days or more, particularly for 7 to 50 days. After a long residence time as described above, the mixture is mixed with phosphorus-containing water in a reaction tank consisting of one tank to obtain a calcium salt of phosphorus, and a coagulant such as polyacrylamide is added to perform coagulation sedimentation treatment. A method has been developed for treating phosphorus-containing water that is returned after a part of the sludge obtained by solid-liquid separation is adjusted to pH 7 to 12. However, in this method, the use of a flocculant increases the processing cost, and also has a problem that sludge excellent in filterability cannot be obtained.

Therefore, an object of the present invention is to remove phosphoric acid in wastewater without using a flocculant and to produce a hydroxyapatite having excellent filterability and dewaterability from wastewater containing phosphoric acid. An object of the present invention is to provide a dephosphorization method. Disclosure of the invention

That is, the present invention uses a treatment apparatus arranged in series in the order of a first crystallization tank, a second crystallization tank, and a sedimentation tank, and uses a treatment apparatus for crystallizing and separating a hydroxy oxyaluminate from a phosphoric acid-containing wastewater. In the dephosphorization method, in the first crystallization tank, the pH of the phosphoric acid-containing wastewater, calcium chloride, and the returned hydroxyapatite slurry returned from the settling tank are adjusted with a pH adjusting agent. The slurry obtained in the first crystallization step and the slurry obtained in the first crystallization step are flowed into the second crystallization tank, and calcium chloride and a pH adjuster are added to the first crystallization tank. Further reaction crystallization was carried out at a pH higher than PT / JP2004 / 001417

In the second crystallization step, the slurry obtained in the second crystallization step is flowed into a settling tank, sedimentation and separation are performed, the supernatant liquid is treated as treated water, and discharged out of the system. It is intended to provide a method for dephosphorizing waste water, which is characterized by using the returned hydroxyapatite slurry. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an example of a treatment apparatus used in the method for dephosphorizing waste water of the present invention, and FIG. 2 is a graph showing a dissolution curve of hydroxyapatite. BEST MODE FOR CARRYING OUT THE INVENTION

The method for dephosphorizing wastewater according to the present invention comprises a first crystallization step, a second crystallization step, a second crystallization step, and a treatment apparatus arranged in series in the order of a first crystallization tank, a second crystallization tank, and a sedimentation tank. Sedimentation is performed sequentially, and hydroxyapatite is separated by crystallization from the wastewater containing phosphoric acid to be treated.

In the first crystallization step, the phosphoric acid-containing wastewater, calcium chloride, and the returned hydroxyapatite (hereinafter referred to as “HAP”) slurry returned from the sedimentation tank flow into the first crystallization tank. . The phosphoric acid-containing wastewater is not particularly limited, and includes, for example, wastewater containing phosphoric acid from several ppm to several weight%, and among them, the phosphoric acid concentration is particularly preferably 100 ppm to 100,000. Suitable for dephosphorization of wastewater containing high concentration of 0 ppm. Specifically, wastewater from a phosphoric acid production plant, a fertilizer plant, a metal surface treatment plant, an electroless plating plant, or a semiconductor component production process, general household wastewater, and sewage treatment wastewater. The calcium chloride is not particularly limited, and industrially available calcium chloride may be used.

Returned HAP slurry refers to HAP slurry concentrated in the sedimentation tank, and the amount supplied per unit time to the first crystallization tank is supplied to the first crystallization tank. The amount of phosphoric acid-containing wastewater supplied per unit time is 100 parts by volume or more, preferably 50 parts by volume or more, and more preferably 100 parts by volume or more. In addition, the supply amount per unit time converted to the solid content of the returned HAP slurry supplied to the first crystallization tank was calculated by converting the phosphoric acid contained in the phosphoric acid-containing wastewater supplied to the first crystallization tank to HAP. The amount is 2500 parts by weight or more, preferably 4000 parts by weight or more, per 100 parts by weight of the supply amount per unit time. The HAP produced in the first crystallization tank is brought into contact with a large amount of HAP seed crystals that are 25 times or more the weight of HAP to precipitate HAP crystals on the HAP particles, and the increased HAP is used in the equipment. By circulating 25 times or more through the inside, HAP with a large particle size of Stokes diameter of 10 zm or more and excellent sedimentation and filtration properties can be obtained. In the first crystallization tank, the concentration of the solid content of the returned HAP slurry is preferably always 2% by weight or more. If the concentration is less than 2% by weight, the amount of seed crystals is too small and HAP is not crystallized on the seed crystals of the returned HAP slurry.

In the first crystallization step, the supply amount of calcium chloride supplied to the first crystallization tank per unit time is determined by converting the phosphoric acid in the phosphoric acid-containing wastewater supplied to the first crystallization tank to HAP. It is to be less than the theoretical equivalent. The reason for keeping the stoichiometric equivalent or less is that in the first crystallization tank, the reaction crystallization is performed in a state where the phosphate ion concentration is high, so the calcium ion, which is the other substance in the reaction, is reduced to reduce the HAP. This is because the solubility increases and the degree of supersaturation can be reduced, and the generation of primary nuclei, which are fine crystals, can be suppressed.

The pH in the first crystallization tank is adjusted to 5.5 to 8.0, preferably to 6.5 to 7.5. The pH adjustment in this case is different from that of pure water, and is between the first and second neutralization points containing phosphate ions. Therefore, pH can be adjusted relatively easily. If the pH is adjusted to 5.5 to 8.0 in the first crystallization tank, the solubility of HAP in the first crystallization tank increases and the supersaturation decreases, so the primary nucleus Generation is suppressed. If the pH is less than 5.5, the crystallized HAP is easily dissolved, which is not preferable.

Examples of the pH adjusting agent used in the first crystallization tank include a basic solution such as sodium hydroxide and a hydrolyzate, and an acidic solution such as hydrochloric acid and nitric acid. Sodium hydroxide is preferable as the basic solution, and hydrochloric acid is preferable as the acidic solution. Although calcium hydroxide, which is a basic solution, is inexpensive, it affects calcium ion concentration as well as pH adjustment. Therefore, when used, it is preferable to use it in combination with sodium hydroxide.

When the pH adjuster used in the first crystallization tank is a basic solution, the basic solution is preferably mixed with the returned hydroxyapatite slurry and then supplied to the first crystallization tank. The reason for this is that the returned HAP slurry has the lowest phosphate ion concentration in the apparatus and is highly alkaline and is optimal as a diluent for basic solutions. This is because the water is supplied to the first crystallization tank, and the pH is not too high locally in the first crystallization tank, and it is difficult to generate fine HAP.

When the pH adjuster used in the first crystallization tank is an acidic solution, the acidic solution is preferably mixed with the phosphoric acid-containing wastewater and then supplied to the first crystallization tank. The reason is that the acidic solution, which is a pH adjuster, is diluted, increased, and dispersed in a large amount of wastewater containing phosphoric acid before it is supplied to the first crystallization tank. This is because the pH does not locally decrease and HAP does not dissolve. In the phosphoric acid-containing wastewater mixed with the acidic solution, no change such as precipitation of crystals was observed.

The location where calcium chloride is added in the first crystallization tank is not particularly limited. JP2004 / 001417

However, as in the case of the acidic solution, it is preferable to supply the mixed solution with the phosphoric acid-containing wastewater to the first crystallization tank. The reason for this is diluted,增amount of calcium chloride, when dispersed in advance phosphoric acid-containing waste water, there can be the _{C a HP 0 4 · 2 H} 2 0 crystals (second phosphate calcium-'dihydrate) However, since 2 mol of hydrochloric acid is generated at the same time, it is better to handle it in the same way as the above-mentioned acidic solution.Also, it is possible to avoid a local high concentration of calcium ion in the first crystallization tank, This is because the generation of an HAP crystal can be suppressed. In the second crystallization step, the HAP slurry obtained in the first crystallization tank is flowed into the second crystallization tank, calcium chloride is added, and the pH is at least higher than the pH of the first crystallization tank, and p H 11 or less, preferably 8.7 or less further causes reaction crystallization. That is, in the second crystallization tank, the concentration of phosphoric acid in the treated water is reduced as much as possible by controlling the region to a high pH region and a high calcium ion concentration region. If the pH exceeds 11 in the second crystallization tank, calcium carbonate and calcium hydroxide are generated, which results in increased consumption of calcium chloride, which is not preferable. Examples of the pH adjusting agent used to keep the pH in the second crystallization tank within the above range include those similar to those used in the first crystallization tank. For the same reason as in the precipitation tank, sodium hydroxide is preferable as the pH adjuster for changing the liquidity to the basic side.

The amount of calcium chloride supplied to the second crystallization tank per unit time is the amount required to convert the equivalent of calcium chloride used in the first crystallization tank and the phosphoric acid in the phosphoric acid-containing wastewater into apatite. The excess is at least 10% by weight or more, preferably 20% by weight or more based on the theoretical equivalent. If the added amount of calcium chloride is insufficient, the unreacted phosphoric acid corresponding to the insufficient amount will flow out.

In the sedimentation separation process, the slurry obtained in the second crystallization tank is flowed into the sedimentation tank, sedimentation and separation are performed, the supernatant liquid is treated water, discharged out of the system, and concentrated. 04001417

Most of the slurry is used as the returned HAP slurry.

The specific amount of the returned HAP slurry is appropriately selected depending on the pH and average reaction time in the first crystallization tank, the concentration of the returned HAP slurry, the particle size of the HAP, and the like, within a range where the treated water does not become cloudy. For example, the supply amount of the returned HAP slurry to be supplied to the first crystallization tank per unit time is as described above, but preferably the phosphorus supplied to the first crystallization tank is not limited. The amount is 50 to 400 parts by volume, preferably 100 to 200 parts by volume, per 100 parts by volume of supply of acid-containing wastewater per unit time. If the return amount of the returned HAP slurry is less than 50 parts by volume, the returned HAP slurry does not sufficiently act as seed crystals in the first crystallized layer, and fine HAP crystals are generated other than the seed crystals to cause sedimentation and separation. Difficult and undesired because the treated water is easily clouded. Also, if the returned amount exceeds 400 parts by volume, the surface area of the HAP seed crystal increases, but the concentration of phosphoric acid in the first crystallization tank becomes too low due to excessive dilution, and the crystallization rate of HAP decreases. However, the average reaction time is shortened and the concentration of phosphoric acid in the treated water is increased, so it seems that there is an appropriate range.

Further, in the present invention, one or more crystallization tanks can be further provided between the first crystallization tank and the sedimentation tank, and the pH in the crystallization tank is the pH in the second crystallization tank. It is preferably higher or the same as it goes downstream, and it is preferably within the range of PH 11 or less.

The crystallization action in the method for dephosphorizing waste water of the present invention is to control so as not to generate fine HAP having poor sedimentation such as a Stokes diameter of 1 zm or less in the first crystallization tank. HAP is deposited on the surface of the returned HAP particles, and the HAP particles are grown. The Stokes diameter here is the equivalent diameter of a particle obtained by assuming that the particle is spherical based on the measured sedimentation velocity according to Stokes' law of resistance. In the case of P, the sedimentation velocity is 3.2 mm / h at l〃m and 3201 at 10〃111] [1111 / h. (For details on the stock diameter, see the Chemical Engineering Dictionary (Chemical Engineering Society, Maruzen Publishing, Pp. 267-268, 3rd edition, revised on March 20, 1986).

In the first crystallization tank, phosphoric acid in the wastewater is brought into contact with HAP seed crystals, which are more than 25 times as large as HAP produced per unit time under the control of pH and calcium, and HAP particles are generated. The HAP deposited on the top and slightly increased in particle size makes it possible to obtain HAP with a large particle size of 10 m or more and good sedimentation and filtration properties by circulating in the tank. . Next, the difference between the treatment in the first crystallization tank and the treatment in the second crystallization tank will be described with reference to FIG. Figure 2, the vertical axis phosphoric acid concentration (phosphorus content), and the horizontal axis: shows the dissolution curve of Hydro O carboxymethyl § Pas tie bets in the case of the _{pH [Ca 5 (OH) (} P 0 4) 3] . In Fig. 2, A is the dissolution curve of HAP at the calcium ion concentration Omg / l in the aqueous solution, B is the dissolution curve of HAP at 4 Omg / l, and C is the dissolution curve of HAP at 10 Omg / l. It is a curve. That is, FIG. 2 shows the relationship between the phosphate concentration, calcium ion concentration and pH in the production and dissolution of HAP. From the comparison of A, B and C, in order to efficiently dephosphorize from wastewater, it is necessary to increase the calcium ion concentration and the pH, that is, to crystallize roughly in the Y region in the figure. I understand. However, in the first crystallization step, if the crystallization is carried out in the Y region immediately, the HAP to be crystallized becomes fine crystals and becomes cloudy, and does not precipitate. Therefore, in the present invention, in the treatment in the first crystallization tank, the highest priority is given to preventing turbidity, that is, increasing the particle size of HAP, and the phosphoric acid concentration is sufficiently reduced only in the first crystallization tank. While recognizing that it will not be used, it is necessary to add a specific amount of the returned HAP slurry as a seed crystal while daringly selecting the low pH region and low calcium ion concentration region. 04 001417

A crystallization treatment that does not produce finer crystals is performed (approximately X region in FIG. 2). Then, in the crystallization treatment after the second crystallization tank, a high pH region and a high calcium ion concentration region are selected ( (Approximately Y region in Fig. 2) This is to reduce the concentration of phosphoric acid in the treated water sufficiently. It should be noted that the X region and the Y region in FIG. 2 are merely described for convenience of explanation, and are not strict or limit the present invention.

An example of a processing apparatus for performing the wastewater dephosphorization method of the present invention is shown by a flow sheet in FIG. The processing apparatus 10 is arranged in series in the order of a first crystallization tank 1, a second crystallization tank 2, and a settling tank 3. Here, the tandem arrangement means that the phosphoric acid-containing wastewater is treated in the order of the first crystallization tank, the second crystallization tank, and the sedimentation tank, and specifically, treated in the first crystallization tank. It means that the treatment liquid treated in the second crystallization tank is supplied to the settling tank while the treatment liquid is supplied to the second crystallization tank. In FIG. 1, the pipe for supplying the processing solution treated in the first crystallization tank 1 to the second crystallization tank 2 is denoted by 21 as a first overflow pipe, and the second crystallization tank 2 A pipe for supplying the processing solution treated in the above only to the settling tank 3 is denoted by 31 as a second overflow pipe. The first crystallization tank and the second crystallization tank are preferably complete mixing tanks that can stir the liquid in the entire tank up and down so that the crystallization reaction can proceed relatively smoothly. . In addition, a return pipe 14 connected to the first crystallization tank 1 is provided below the settling tank 3, and a slurry pump 16 is provided in the set pipe 14. The lowered HAP slurry is supplied to the first crystallization tank 1 by a slurry pump 16. When the generated HAP increases in the slurry remaining at the bottom of the settling tank and the slurry level rises, the slurry is extracted into the slurry tank, and the HAP cake is taken out once a day or three days by a fill and press machine.

(Example)

Next, the present invention will be described more specifically with reference to examples. It is an exemplification and does not limit the present invention.

Examples 1, 2 and Comparative Example 1

Phosphoric acid-containing wastewater was subjected to dephosphorization treatment using a treatment apparatus 10 represented by a flow sheet shown in FIG. The first crystallizer 1 and the second crystallization vessel 2 has a diameter 2 4 0 0 thigh, height 4 2 0 0 mm, an effective volume 1 6 m ^3, and diameter under water at the center of the vessel A downcomer with a height of 600 mm and a height of 2700, and a stirrer with a variable transmission having blades with a diameter of 550 orchids inside the downcomer, and the whole tank is operated by operating the stirrer. A complete mixing tank capable of vertically flowing the liquid or slurry was used.

First, raw water of phosphoric acid-containing wastewater discharged from a plurality of facilities was introduced into raw water tank 4 via pipe 41, and mixed in raw water tank 4 to make the concentration uniform. As a result, the wastewater containing phosphoric acid in the raw water tank 4 had the composition shown in Table 1. Further, the calcium chloride slurry in the calcium chloride storage tank 8 and the sodium hydroxide aqueous solution in the sodium hydroxide storage tank 7 were prepared to have the compositions shown in Table 1, respectively. The operation in this example was performed in a steady state.

(First crystallization step)

First, the phosphoric acid-containing wastewater was supplied from the raw water tank 4 to the liquid surface of the first crystallization tank 1 via the pipe 11 using the pump 15 under the conditions shown in Table 2 “Phosphoric acid-containing wastewater”. . It should be noted that the pipe 12 connected to the calcium chloride storage tank 8 was connected just before the pipe 11 to the first crystallization tank, and the phosphoric acid-containing wastewater and the chloride slurry were mixed before the first crystallization tank was mixed. To be supplied. The calcium chloride slurry was supplied using a pump 24 under the conditions shown in Table 2 “Calcium chloride solution”. Further, the returned HAP slurry was supplied onto the liquid surface of the first crystallization tank 1 via the pump 16 and the return pipe 14 under the conditions shown in Table 2. In addition, sodium hydroxide solution It was supplied appropriately from the storage tank 7 and adjusted so that the pH in the first crystallization tank 1 became the value shown in Table 2. At this time, the pipe 22 leading to the sodium hydroxide storage tank 7 was connected to the return pipe 14 so as to join immediately before the first crystallization tank, and the aqueous sodium hydroxide solution and the returned HAP slurry were mixed. After that, it was supplied to the first crystallization tank. The average residence time in the first crystallization tank 1 was about 1.1 hours.

(Second crystallization step)

The obtained slurry in the first crystallization tank was continuously transferred to the second crystallization tank via the first overflow pipe 21. In the second crystallization tank 2, HAP was crystallized under the conditions shown in Table 3. The sodium hydroxide and calcium chloride solutions of the pH adjusters were each diluted with 100 L / h of water, increased in volume, and dispersed and supplied. The slurry of the second crystallization tank treated in the second crystallization tank was continuously transferred to the settling tank via the second overflow pipe 31.

(Sedimentation separation process)

In settling tank 3, HAP was settled under the conditions shown in Table 4. After the sedimentation treatment, the obtained supernatant was continuously discharged through the third overflow pipe 32 and used as treated water. Table 5 shows the composition of the treated water. On the other hand, the HAP slurry settled in the lower part of the settling tank 3 is returned to the first crystallization tank 1 through the return pipe 14 via the pump 16 via the pump 16 to form a returned HAP slurry. Once the level increased, once every 1 to 3 days, the slurry was transferred from the receiving tank 5 to the filter press 6 via the pump 17 and separated into cake and filtered water. Since the cake did not contain a coagulant and did not stick, it could be easily separated and separated from the film, and the cake after separation could be easily dried. Further, the filtered water was returned to the raw water tank 4 through the pipe 42 so that even when the HAP slurry leaked due to leakage of the filter cloth or the like, it did not flow out as wastewater to the outside. Treated water Table 5 shows the amount of phosphoric acid and the dephosphorization rate.

Table 1

Raw material composition Unit Example Example Example Comparative example

1 2 1

1) Right now !: Ma 3

Phosphoric acid concentration p pm 720 1090 620 j R «7? 7? Calcium chloride solution composition

Calcium chloride concentration Sato · & ⁰ // 0 35 35 35 Return HAP slurry composition

0 /

Slurry concentration ο 5.1 6.6 4.7 Stokes diameter of slurry 11.3 12.0 10.2 Composition of aqueous sodium hydroxide solution

Sodium hydroxide concentration ¾mo /

Sato / 0 25 25 25

2 tables

) Solid content conversion

Table 3 Conditions for second crystallization tank Unit Example Example Example Comparative example

1 2 1 Effective volume m ³ 16 16 16 First crystallization tank slurry

Inflow m ³ / h 14.4 15.1 14.5 Calcium chloride solution

Inflow L / h 15 10 10 Calculated amount of calcium chloride kg / h 6.8 4.6 4.6% 70 43 40 Calculated as calcium chloride supplied to the second crystallization tank per unit time

Process per unit time

Calcium chloride suitable for phosphoric acid

Conversion amount

PH in the second crystallization tank 8.3 8.5 8.2 Average residence time in the second crystallization tank Time 1.1 1.1 1.1

Conditions in the settling tank Unit Example Example Example Comparative example

1 2 1 Second crystallization tank slurry

Inflow m ³ / 14.5 15.2 14.6 pH in sedimentation tank 8.3 8.5 8.1 Table 5

Industrial applicability

According to the method for removing phosphorus from wastewater according to the present invention, phosphoric acid in wastewater can be removed without using a coagulant. In addition, the cake obtained by pressing the filter after settling and separation does not contain coagulant and does not stick, so it can be easily separated from the filter and separated, and the cake after separation can be easily dried. Cost can be reduced.

Claims

The scope of the claims

1. Using a treatment device that is arranged in series in the order of the first crystallization tank, the second crystallization tank, and the sedimentation tank, the crystallization separation of hydroxyapatite from the phosphoric acid-containing waste water In the first crystallization tank, the phosphoric acid-containing waste water, calcium chloride, and the returned hydroxyapatite slurry returned from the sedimentation tank are reacted and crystallized while adjusting the pH with a pH adjusting agent. (1) The crystallization step, the slurry obtained in the first crystallization step is allowed to flow into a second crystallization tank, and calcium chloride and a pH adjuster are added to increase the pH of the first crystallization tank, and Second crystallization step for further reaction crystallization under 1 and below, The slurry obtained in the second crystallization step is flowed into the sedimentation tank, sedimentation separation is performed, and the supernatant liquid is treated water to outside the system. Discharge and return most of the concentrated slurry to the A method for dephosphorizing wastewater, which comprises using apatite slurry.

2. The supply amount of the returned hydroxyapatite slurry to be supplied to the first crystallization tank per unit time is equal to the supply amount of the phosphoric acid-containing wastewater to be supplied to the first crystallization tank per unit time. 2. The method for dephosphorizing wastewater according to claim 1, wherein the amount is 50 parts by volume or more with respect to 100 parts by volume.

3. The supply amount per unit time, which is converted into the solid content of the returned hydroxyapatite slurry supplied to the first crystallization tank, is equal to the phosphoric acid-containing wastewater supplied to the first crystallization tank. 3. The method according to claim 1, wherein the amount of the phosphoric acid is not less than 250 parts by weight based on 100 parts by weight of the supplied amount per unit time in terms of hydroxyapatite. How to remove phosphorus from wastewater.

4. The supply amount of the calcium chloride supplied to the first crystallization tank per unit time is such that the phosphoric acid of the phosphoric acid-containing wastewater supplied to the first crystallization tank is converted into a hydroxyapatite. Converting to less than the required theoretical equivalent The method for dephosphorizing wastewater according to any one of claims 1 to 3, characterized in that:

5. The supply amount of the calcium chloride per unit time supplied to the second crystallization tank depends on the equivalent shortage of the calcium chloride supplied to the first crystallization tank. The method for removing phosphorus from wastewater according to any one of claims 1 to 4, wherein the total amount of the excess amount is at least 10% or more based on the theoretical equivalent required for converting the wastewater into an aperitite. .

6. When the pH adjuster used in the first crystallization tank is a basic solution, the basic solution is mixed with the returned hydroxyapatite slurry and then supplied to the first crystallization tank. The method for dephosphorizing wastewater according to any one of claims 1 to 5, which is characterized in that:

7. When the pH adjuster used in the first crystallization tank is an acid solution, the acid solution and the calcium chloride are mixed with the phosphoric acid-containing wastewater and then supplied to the first crystallization tank. The method for removing phosphorus from wastewater according to any one of claims 1 to 6.

8. The method for removing waste water according to any one of claims 1 to 7, wherein the pH adjuster used in the first crystallization tank is sodium hydroxide or hydrochloric acid.

9. One or more crystallization tanks are further provided between the second crystallization tank and the sedimentation tank, and the pH in the crystallization tank is downstream of the pH in the second crystallization tank. 9. The dewatering of the drainage water according to claim 1, wherein the water content is sequentially higher or the same as the pressure becomes higher, and is within a range of pH 11 or less. Method.