JP2010017631A - Method and apparatus for treating phosphoric acid-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently treat wastewater, such as flat panel display (FPD) manufacturing wastewater, containing organic acids such as phosphoric acid, nitric acid, and acetic acid while suppressing the amount of used chemical without causing trouble such as scale deposition by phosphoric acid-removing treatment using a calcium compound and subsequent biological denitrification treatment. <P>SOLUTION: In a method for treating phosphoric acid-containing water, the calcium compound is added to the phosphoric acid-containing water, and the pH is adjusted to 6.5 or less. The precipitated apatite phosphate is solid-liquid separated, and the separated water is subjected to calcium-removing treatment and then to the biological denitrification treatment. The biologically denitrified water is further subjected to desalting treatment. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for treating water containing organic acids such as phosphoric acid, nitric acid and acetic acid, such as flat panel display (FPD) production waste water.

  FPD production wastewater contains phosphoric acid, nitric acid, acetic acid, and the like, and it is necessary to remove them in order to discharge this wastewater.

  Conventionally, as a method for treating FPD production wastewater, first, phosphoric acid in wastewater is removed, and then nitric acid and acetic acid are removed by biological denitrification treatment. Phosphoric acid in the wastewater is added with a high concentration of calcium compounds such as slaked lime to the wastewater, and pH 5.5 to 8.0. Desirably, the coagulation treatment is performed under conditions of 6.5 to 7.5, and the neutralization is performed in two stages in which the coagulation treatment is performed in the second stage at a pH higher than that of the first stage and a pH of 11 or less, preferably 8.7 or less. An aggregation treatment is performed to remove phosphoric acid as phosphate apatite (Patent Document 1).

  That is, phosphoric acid in wastewater is reacted with calcium compounds to cause coagulation and precipitation, and in order to remove phosphoric acid to the standard value of wastewater, phosphoric acid and calcium compounds are reacted in the alkaline pH range to react with phosphorus. Since it is necessary to form a precipitate of acid apatite (hydroxyapatite), conventionally, agglomeration treatment is performed under pH alkaline conditions. FIG. 3 is a graph showing the relationship between the solubility of phosphate apatite and pH. As is clear from this graph, it is preferable to adjust the pH to about 8.5 in order to remove phosphoric acid to a high degree.

  However, in this method, pH alkaline phosphate removal treatment water containing a large amount of residual calcium ions and a small amount of residual phosphate ions flows into the biological denitrification process, so that calcium phosphate and carbonate in the biological denitrification system. There was a problem that scale components such as calcium were deposited, clogging the piping, and adversely affecting biological treatment.

  In addition, the phosphate apatite produced by the reaction can be applied to uses as artificial tooth roots, artificial bone materials, adsorbents, various catalysts, humidity sensors, etc. It is desirable to recover acid apatite with high purity, but under pH-alkaline conditions, carbonate ions and calcium ions in water are likely to bind to form calcium carbonate, and this calcium carbonate is contained in phosphate apatite. There is also a problem that the purity of phosphate apatite is reduced by mixing.

Regarding the problem of scale precipitation, it is possible to remove calcium ions in water by ion-exchange treatment and desalting treatment of phosphoric acid-removed water to prevent such scale precipitation. However, there is a problem in that the phosphoric acid-removed treated water having a high salt concentration is ion-exchanged with an ion-exchange resin, the ion-exchange resin is regenerated frequently and a large amount of regenerative medicine is required. Among the ion exchange resins, an anion exchange resin regeneration waste liquid contains nitric acid and acetic acid that are contained in phosphoric acid removal treated water and ion-exchanged with the anion exchange resin. For this reason, this regenerated waste liquid needs to be further biologically denitrified, but since this regenerated waste liquid has a high salt concentration, it is necessary to dilute it prior to charging it into the biological denitrification tank. Need to be neutralized. Furthermore, an acid for neutralizing the increase in pH associated with the denitrification reaction is required, and the necessary amount of acid for neutralization becomes excessive.
JP 2004-261640 A

  The present invention solves the above-mentioned conventional problems, and wastewater containing organic acids such as phosphoric acid, nitric acid and acetic acid, such as FPD production wastewater, is subjected to phosphoric acid removal treatment using a calcium compound and subsequent biological denitrification treatment. It is an object of the present invention to provide a technique for efficiently processing without causing troubles such as scale deposition and suppressing the amount of drug used.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor produces phosphate apatite with good dehydration by performing phosphoric acid removal treatment in which a calcium compound is added under low pH conditions. By removing the calcium ions remaining in the separated water obtained by separation and performing biological denitrification treatment under conditions where scales such as calcium phosphate do not precipitate, scale failure in the biological denitrification step can be prevented, It has been found that high-quality treated water can be recovered by subjecting this biological denitrification treated water to desalination.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] A method for treating phosphoric acid-containing water containing phosphoric acid, nitric acid and an organic acid, the reaction step of adding a calcium compound to the phosphoric acid-containing water and adjusting the pH to 6.5 or less, and the reaction step A solid-liquid separation step for solid-liquid separation of the phosphate apatite precipitated in step 1, a decalcification step for removing calcium from the separated water separated by solid-liquid separation in the solid-liquid separation step, and biological denitrification of the treated water in the decalcification step And a biological denitrification step to be treated.

[2] A method for treating phosphoric acid-containing water according to [1], including a desalting step of desalting the treated water in the biological denitrification step.

[3] The method for treating phosphoric acid-containing water according to [1] or [2], further comprising a sludge return step for returning a part of the sludge separated in the solid-liquid separation step to the reaction step.

[4] A treatment apparatus for phosphoric acid-containing water containing phosphoric acid, nitric acid, and organic acid, a reaction means for adding a calcium compound to the phosphoric acid-containing water and adjusting the pH to 6.5 or less, and the reaction means A solid-liquid separation means for solid-liquid separation of the phosphate apatite deposited in step 1, a decalcification means for removing calcium from the separated water solid-liquid separated by the solid-liquid separation means, and biological denitrification of the treated water of the decalcification means An apparatus for treating phosphoric acid-containing water, comprising biological denitrification means for treatment.

[5] The apparatus for treating phosphoric acid-containing water according to [4], further comprising a desalting means for desalting the treated water of the biological denitrification means.

[6] The apparatus for treating phosphoric acid-containing water according to [4] or [5], further comprising sludge return means for returning a part of the sludge separated by the solid-liquid separation means to the reaction means.

  In the present invention, by adding a calcium compound to phosphoric acid-containing water and reacting under a low pH condition of pH 6.5 or less, phosphoric acid is precipitated as phosphate apatite with good dehydration properties, and this is solid-liquid separated. And remove.

In the phosphoric acid removal treatment under the low pH condition, a slight amount of phosphoric acid remains, but the remaining phosphoric acid can be removed by the subsequent biological denitrification treatment and further the desalting treatment.
Moreover, under this low pH condition, the production of calcium carbonate is suppressed, and high-purity phosphate apatite free from calcium carbonate can be recovered.

  In addition, when a high concentration phosphoric acid and a calcium compound such as calcium hydroxide are mixed, fine phosphate apatite crystals are formed. With such fine crystals, good solid-liquid separability cannot be obtained. By returning sludge (phosphate apatite crystals) to this reaction system, phosphate apatite precipitates on the surface of the returned sludge as a nucleus and can be grown into large crystals, resulting in good solid-liquid separation. (Claims 3 and 6).

  In the present invention, the calcium ions remaining in the phosphoric acid removal treatment are removed in the subsequent decalcification step, thereby preventing scale failure in the subsequent biological denitrification step.

  When this decalcification process is not performed, nitric acid and acetic acid exist as calcium nitrate and calcium acetate, respectively. Therefore, in the biological denitrification process, nitric acid and acetic acid are decomposed and removed by the following reaction. PH increases.

8Ca (NO ₃ ) ₂ +5 (CH ₃ COO) ₂ Ca
→ 8N ₂ + 13Ca (OH) ₂ + 20CO ₂ + 2H ₂ O
→ 8N ₂ + 10Ca (HCO ₃ ) ₂ + 3Ca (OH) ₂ + 2H ₂ O
→ 8N ₂ + 6CaCO ₃ (precipitation) + 7Ca (HCO ₃ ) ₂ + 5H ₂ O

  For this reason, the conventional biological denitrification treatment requires the addition of an acid to neutralize this pH increase.

On the other hand, in the present invention, since calcium ions are removed in the decalcification step preceding the biological denitrification step, nitric acid and acetic acid are present in the form of acids, respectively. It becomes the main component and hardly raises the pH. For this reason, acid addition for neutralization becomes unnecessary, and the amount of medicine used can be reduced.
_{8HNO 3 + 5CH 3 COOH → 4N} 2 + 10CO 2 + 14H 2 O

  In the present invention, after the biological denitrification step, it is preferable to further perform a desalting treatment, whereby high-quality treated water (pure water) can be obtained (claims 2 and 5).

  In this case, since nitrate ions and acetate ions are removed in the biological denitrification step, even when the desalting treatment is performed using an ion exchange resin, the ion load, particularly the anion load, is small. The amount of regenerant used in the ion exchange resin, especially the amount of alkali (sodium hydroxide) used, can be greatly reduced.

  Embodiments of a method and apparatus for treating phosphoric acid-containing water according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment of a treatment apparatus for phosphoric acid-containing water of the present invention, wherein 1 is a reaction tank, 2 is a precipitation tank, 3 is a filter, 4 is a decalcification tower (decalcification tower), 5 is a biological denitrification tank, 6 is a filter, and 7 is a two-bed ion exchange device, which includes a cation exchange column 7A and an anion exchange column 7B.

  The phosphoric acid-containing water (hereinafter referred to as “raw water”) to be treated in the present invention is water containing phosphoric acid and organic acids such as nitric acid and acetic acid, for example, FPD production wastewater such as liquid crystal production wastewater, Examples include semiconductor manufacturing wastewater and electrolytic capacitor manufacturing wastewater. Although there is no restriction | limiting in particular as the water quality, Usually, it is the following water quality.

<Raw water quality>
pH: 1.5-2.5
H ₃ PO ₄ -P: 200 to 2000 mg-P / L
HNO ₃ : 30 to 600 mg / L
CH ₃ COOH: 30~600mg / L

  In the present invention, the calcium compound is first added to such raw water in the reaction tank 1 and adjusted to pH 6.5 or less.

  There is no restriction | limiting in particular as a calcium compound added to raw | natural water, Calcium hydroxide (slaked lime), calcium carbonate, calcium bicarbonate, calcium chloride etc. can be used. These may be used alone or in combination of two or more. However, calcium chloride is not so preferred because chlorine ions increase.

  The amount of calcium compound added is appropriately determined according to the phosphoric acid concentration in the raw water, and is usually about 0.9 to 0.99 times the reaction equivalent of phosphoric acid in the raw water. For example, when the calcium compound is calcium hydroxide For example, it is preferable that the amount is about 1.9 to 2.1 times the weight of P in terms of phosphoric acid in the raw water. If the amount of calcium compound added is too small, phosphoric acid cannot be removed sufficiently, and if it is too large, the load on the subsequent Ca removal step increases, which is not preferable.

  If the pH of the reaction system when the calcium compound is added to the raw water for reaction is higher than 6.5, scale failure occurs in the biological denitrification process in the subsequent stage. However, if the pH value is excessively low and less than 5.5, phosphate apatite becomes difficult to precipitate. Therefore, this pH value is preferably 5.5 to 6.5, particularly preferably 6.0 to 6.5. Therefore, the pH is adjusted to this pH range by adding an acid or an alkali as necessary together with the addition of the calcium compound.

  In the reaction under such pH conditions, phosphoric acid in the raw water cannot be removed to a high degree as in the reaction under high pH conditions, but about 8 to 90 mg-P / L of phosphoric acid remains. Since this phosphoric acid is partly used in the subsequent biological denitrification treatment, is removed by apatite formation due to the increase in pH, and is further removed by the desalting treatment, there is no problem.

  Usually, the raw water to be treated of the present invention containing an organic acid such as phosphoric acid, nitric acid, and acetic acid is strongly acidic water as described above, so an alkali is added as a pH adjuster. Therefore, it is preferable to use calcium hydroxide, calcium carbonate, or calcium bicarbonate, which are alkaline agents, as the calcium compound, and to combine pH adjustment and calcium compound addition.

  Although there is no restriction | limiting in particular in reaction time, It is preferable to make it the residence time in the reaction tank 1 become about 5 to 30 minutes.

  As described above, the addition of a calcium compound produces fine phosphate apatite crystals and does not provide sufficient solid-liquid separation. Therefore, in the apparatus shown in FIG. A part of the separated sludge is returned to the reaction tank 1.

  By returning the sludge in this way, the crystals of phosphate apatite are precipitated and coarsened on the surface of the returned sludge, so that good solid-liquid separation can be obtained.

  If the amount of returned sludge is too small, the above-mentioned effect by returning the sludge cannot be obtained sufficiently, and if it is too large, the required reaction tank capacity increases, which is not preferable. Usually, the amount of sludge returned is preferably about 5 to 50 times the amount of phosphate apatite produced by adding a calcium compound to the raw water as its solid content.

  The returned sludge may be mixed with some or all of the calcium compounds added to the raw water and added to the raw water.

  The reaction liquid in the reaction tank 1 is fed to the precipitation tank 2 and separated into solid and liquid, a part of the separated sludge is returned to the reaction tank 1, and the remainder is discharged out of the system as surplus sludge. This excess sludge contains phosphate apatite having a relatively high purity, and can be applied to various uses.

  On the other hand, the separated water is fed to the Ca removal tower 4 after the SS is further removed by the filter 3. This filter 3 plays a role as a filter for preventing clogging of the de-Ca tower 4, and a downward flow sand filter or the like can be used.

  The Ca removal tower 4 is a cation exchange tower filled with a cation exchange resin. In the Ca removal tower 4, calcium ions in the filtered water of the filter 3 are removed.

  Since the ion exchange capacity is saturated by the filtered water flow treatment, the Ca removal tower 4 needs to be periodically regenerated with a regenerant (hydrochloric acid). This regenerated waste liquid is neutralized with sodium hydroxide and then drained.

  In this invention, this calcium removal should just be implemented to such an extent that a scale obstacle does not generate | occur | produce in a biological denitrification process of a latter stage, Therefore, the whole quantity of the filtered water (phosphoric acid removal process water) from a filter is removed from Ca. There is no need to process. For example, about 10 to 90% of the filtered water may be fed to the deCa tower 4 to be decalcified, and the remainder may be directly introduced into the biological denitrification tank 5 at the subsequent stage. Thus, the regeneration frequency of the Ca removal tower 4 can be reduced by performing Ca removal treatment on only part of the phosphoric acid removal treated water.

  The calcium concentration at which calcium scale is not generated in the denitrification reaction tank 5 varies depending on the pH conditions. For example, at pH 5.5 to 6.5, the Ca ion concentration is 150 mg / L or less. What is necessary is just to determine the ratio which carries out Ca removal process so that Ca ion concentration of 5 inflow water may be 100 mg / L or less.

In the denitrification reaction tank 5, as described above, nitric acid and acetic acid are decomposed and removed mainly in accordance with the following reaction formula. In addition, part of the phosphoric acid is also taken up by the cells. In this case, when either nitric acid or acetic acid is insufficient for the reaction, an insufficient amount is appropriately added.
_{8HNO 3 + 5CH 3 COOH → 4N} 2 + 10CO 2 + 14H 2 O

  As described above, in this denitrification reaction, although there is an increase in pH, even if the pH is increased, the pH is about 7 to 8, so that an acid addition for adjusting the pH is unnecessary.

  In FIG. 1, although not shown, the denitrification reaction tank 5 includes a biological reaction tank and a precipitation tank for solid-liquid separation of the biological treatment liquid from the biological reaction tank, or a membrane immersion reaction in which a separation membrane is immersed. The solid-liquid separation liquid from the biological denitrification tank 5 is filtered by a filter 6 and then desalted by a two-bed ion exchanger 7. In the case where a separation membrane is used as the solid-liquid separation means, the filter 6 is omitted.

  Like the filter 3, this filter 6 also serves as a filter for preventing clogging of the cation exchange column 7A and the anion exchange column 7B of the two-bed ion exchange device 7, and is a downward flow type. A sand filter or the like can be used.

  In the two-bed ion exchange apparatus 7, first, cations are removed by the cation exchange column 7A, and anions are removed by the anion exchange column 7B.

  Each of the ion exchange towers 7A and 7B is also regenerated periodically or as necessary. In the present invention, water introduced into the two-bed ion exchange apparatus 7 is phosphoric acid, nitric acid, acetic acid or the like. Since it is water from which organic acids and calcium ions have been removed in advance, the frequency of regeneration is low, and the amount of regenerant used can be reduced. In particular, even when the amount of regenerant (hydrochloric acid) used in the previous stage of decalcification tower 4 is taken into account, the regeneration frequency of the anion exchange tower of this two-bed ion exchanger 7 is low. The amount of sodium oxide) used can be greatly reduced. The regenerated waste liquids of the cation exchange column 7A and the anion exchange column 7B are neutralized with acid and alkali. However, in the present invention, the amount of regenerated waste liquid is also small, so the load of waste liquid treatment is greatly reduced.

  Thus, the treated water obtained by further removing cations and anions from the biological denitrification treated water with a two-bed type ion exchanger is high-quality pure water, which is recovered to obtain a liquid crystal substrate and a semiconductor capacitor. It can be used for raw water for cleaning.

  FIG. 1 shows an example of an embodiment of the present invention, and the present invention is not limited to the method shown in FIG. 1 as long as the gist thereof is not exceeded. For example, biological denitrification treatment As a means for desalting water, a reverse osmosis membrane separation device, a continuous electrodeionization device or the like can be used in addition to an ion exchange device. When these devices are used, ion exchange when using an ion exchange device is used. It is not necessary to regenerate the resin. In addition, when applying a reverse osmosis membrane separation apparatus, in order to prevent calcium scale from precipitating due to concentration, an acid that does not form calcium ions and hardly soluble salts is added to the filtered water of the filter 6 to adjust the pH. It is preferable to adjust to about 3 to 5 to suppress scale deposition of calcium carbonate or calcium phosphate.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

The raw water treated in the following is liquid crystal production waste water having the following water quality.
<Raw water quality>
pH: 2.0
H ₃ PO ₄ -P: 1300 mg-P / L
HNO ₃ : 138 mg / L
CH ₃ COOH: 127 mg / L

[Example 1]
The raw water was treated by the apparatus shown in FIG.
In the reaction tank 1, calcium hydroxide was added to the raw water so that the pH of the water in the tank was 6.5, and the reaction was allowed to proceed for 15 minutes. The amount of calcium hydroxide added at this time was about 5600 mg / L. A part of the separated sludge from the subsequent sedimentation tank 2 was returned to the reaction tank 1. The amount of sludge returned was 20 times the amount of phosphate apatite produced by adding calcium hydroxide to the raw water as a solid content.

The quality of the filtrate water obtained by filtering the supernatant water of the precipitation tank 2 with the filter 3 was as follows.
<Filtered water quality>
pH: 6.5
H ₃ PO ₄ -P: 10 mg-P / L
HNO ₃ : 138 mg / L (2.2 meq / L)
CH ₃ COOH: 127 mg / L (2.1 meq / L)
Ca ion: 90 mg / L (4.5 meq / L)

  A part (about 90%) of this filtered water was passed through a de-Ca tower 4 filled with a strongly acidic cation exchange resin “DIAION SK1B” manufactured by Mitsubishi Chemical Corporation to remove Ca.

  The decalcified Ca water and the remaining filtered water were mixed and denitrified in the biological denitrification tank 5. Nitric acid was added to the biological denitrification tank 5 to replenish the shortage of nitrogen.

  The biological denitrification treated water is separated by precipitation, further filtered through a filter 6, and then a cation exchange tower 7A filled with a strong acid cation exchange resin “Diaion SKIB” manufactured by Mitsubishi Chemical Corporation, and a strong base manufactured by Mitsubishi Chemical Corporation. The anion exchange column 7B filled with the functional anion exchange resin “Diaion SKIIA” was desalted in a two-bed type ion exchanger 7 to collect treated water.

  Table 1 shows the quality of biological denitrification water and the quality of demineralized water (final treated water).

From Table 1, it can be seen that the ion load of the two-bed ion exchanger 7 is reduced by the treatment of the present invention, and the amount of water passing through the ion exchanger can be increased.
Table 2 shows the amount of regenerant in the cation exchange tower 7A and the anion exchange tower 7B of the de-Ca tower 4 and the two-bed type ion exchange apparatus 7 required per 100 m ^{3 of} treated water in this treatment.

[Comparative Example 1]
In Example 1, as shown in FIG. 2, the Ca removal tower 4 and the filter 6 are omitted, and the filtered water from the filter 3 is directly introduced into the two-bed type ion exchange device 7 for the desalination treatment. The treatment was performed in the same manner except that the denitrification tank 5 was installed for the treatment of the regenerated waste liquid of the two-bed ion exchange device 7.
Table 2 shows the amount of regenerant required per 100 m ^{3 of} treated water in this treatment.

In this treatment, the regeneration waste liquid of the anion exchange tower 7B of the two-bed ion exchange device 7 contains nitric acid and acetic acid at high concentrations, and thus denitrification treatment was necessary. In the denitrification treatment, neutralization was carried out by mixing in the regeneration waste liquid of the cation exchange tower 7A and the regeneration waste liquid mixing tank 10, but since the salt concentration is high, it is necessary to dilute it 5 times and perform biological denitrification treatment. Moreover, it was necessary to add hydrochloric acid to adjust pH during the biological denitrification treatment.
The amount of hydrochloric acid added for pH adjustment required per 100 m ^{3 of} treated water was as shown in Table 2.

  From Table 2, it can be seen that according to the present invention, the amount of acid and alkali chemicals used can be greatly reduced and efficient treatment can be performed.

[Example 2]
In Example 1, the treatment was performed in the same manner except that calcium hydroxide was added so that the pH in the reaction tank 1 was 6.0 (calcium hydroxide addition amount 5200 mg / L).
Table 3 shows the quality of the supernatant of the sedimentation tank 2 and the quality of the biological denitrification water. In addition, Table 4 shows the chemical usage required for each process per 100 m ^{3 of} treated water.
As shown in these tables, the amount of drug used in Example 2 increased by about 10% and was less than that in Comparative Example 1.

[Example 3]
In Example 1, it processed similarly except having added calcium hydroxide so that pH in the reaction tank 1 might be set to 5.0 (calcium hydroxide addition amount 4900 mg / L).
Table 3 shows the quality of the supernatant of the sedimentation tank 2 and the quality of the biological denitrification water. In addition, Table 4 shows the chemical usage required for each process per 100 m ^{3 of} treated water.
As shown in these tables, in Example 3, the pH was low, and it was necessary to neutralize by adding 400 mg / L of sodium hydroxide for denitrification.

[Comparative Example 2]
In Example 1, the treatment was performed in the same manner except that calcium hydroxide was added so that the pH in the reaction vessel 1 was 7.0 (calcium hydroxide addition amount 5900 mg / L).
Table 3 shows the quality of the supernatant of the sedimentation tank 2 and the quality of the biological denitrification water. In addition, Table 4 shows the chemical usage required for each process per 100 m ^{3 of} treated water.
As shown in these tables, in Comparative Example 2, since the pH was high in the precipitation tank, the amount of calcium carbonate produced was large and the amount of calcium hydroxide added was increased. Further, the purity of the recovered phosphate apatite was reduced by 10%.

It is a systematic diagram which shows embodiment of the processing apparatus of the phosphoric acid containing water of this invention. 2 is a system diagram of an apparatus used in Comparative Example 1. FIG. It is a graph which shows the relationship between the solubility of phosphate apatite, and pH.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction tank 2 Precipitation tank 3 Filter 4 De-Ca tower 5 Biological denitrification tank 6 Filter 7 Two-bed type ion exchange apparatus 7A Cation exchange tower 7B Anion exchange tower

Claims (6)

A method for treating phosphoric acid-containing water containing phosphoric acid, nitric acid and organic acid,
A reaction step of adding a calcium compound to the phosphoric acid-containing water and adjusting the pH to 6.5 or lower;
A solid-liquid separation step for solid-liquid separation of the phosphate apatite precipitated in the reaction step;
A decalcification step of removing calcium from the separated water separated in the solid-liquid separation step;
A method for treating phosphoric acid-containing water, comprising a biological denitrification step of biologically denitrifying the treated water in the decalcification step.   The method for treating phosphoric acid-containing water according to claim 1, further comprising a desalting step of desalting the treated water in the biological denitrification step.   3. The method for treating phosphoric acid-containing water according to claim 1, further comprising a sludge returning step of returning a part of the sludge separated in the solid-liquid separation step to the reaction step. An apparatus for treating phosphoric acid-containing water containing phosphoric acid, nitric acid and organic acid,
A reaction means for adding a calcium compound to the phosphoric acid-containing water and adjusting the pH to 6.5 or lower;
Solid-liquid separation means for solid-liquid separation of the phosphate apatite precipitated by the reaction means;
Decalcification means for removing calcium from the separated water solid-liquid separated by the solid-liquid separation means;
A treatment apparatus for phosphoric acid-containing water, comprising biological denitrification means for biologically denitrifying treatment water of the decalcification means.   The apparatus for treating phosphoric acid-containing water according to claim 4, further comprising a desalting means for desalting the treated water of the biological denitrification means.   6. The apparatus for treating phosphoric acid-containing water according to claim 4 or 5, further comprising a sludge return means for returning a part of the sludge separated by the solid-liquid separation means to the reaction means.

Images