JPH1110194A - Wastewater treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover a part of wastewater as magnesium ammonium phosphate by providing an anaerobic treatment tank, a reaction tank into which treated liquid of the anaerobic treatment tank is introduced, and a denitrification tank into which treated liquid of the reaction tank is introduced or an aerobic treatment tank. SOLUTION: Wastewater is introduced into an anaerobic tank 1 together with a return sludge from a settling tank 3 of a succeeding stage, where phosphorus in the return sludge is discharged on the side of liquid under anaerobic conditions. The treated anaerobic liquid is then introduced into a magnesium ammonium phosphate(MAP) reaction tank 6, where the phosphorus is caused to react with ammonia and Mg compounds to produce MAP. The MAP reaction liquid, from which phosphorus and ammonia have been removed by the production of the MAP, is then fed into an aerobic tank 2, where BOD is removed under conditions of aeration. And the aerobic treated liquid is introduced into the settling tank 3 so as to be separated to solids and liquid and the separated liquid is discharged to the outside as treated water. On the other hand, separated sludge which takes in phosphorus in the form of orthophosphoric acid by a biological treatment is returned to the tank 1 as return sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment apparatus containing phosphorus and nitrogen, and more particularly to a wastewater treatment apparatus capable of removing phosphorus and nitrogen from wastewater and recovering them as crystals.

[0002]

2. Description of the Related Art A conventional general biological dephosphorization treatment apparatus comprises:
As shown in FIG. 5, it is composed of an anaerobic tank 1, an aerobic tank 2, and a sedimentation tank 3. In this treatment apparatus, the organic wastewater containing phosphorus is flown into the anaerobic tank 1 to release phosphorus in the activated sludge, and then is flown into the aerobic tank 2 to remove excess phosphorus in the activated sludge when performing BOD removal. Remove ingested phosphorus.

As shown in FIG. 6, a conventional general biological dephosphorization and denitrification treatment apparatus includes an anaerobic tank 1, a denitrification tank 4, a nitrification tank 5, and a sedimentation tank 3. In this treatment apparatus, organic wastewater containing phosphorus and nitrogen flows into the anaerobic tank 1 to release phosphorus in the activated sludge, and then flows into the denitrification tank 4 to perform denitrification using BOD in the wastewater. Then, a part of the solution that has been further subjected to the nitrification reaction is returned to the denitrification tank 4.
In the nitrification tank 5, phosphorus is excessively taken into activated sludge under aerobic conditions.

As a method of treating phosphorus-containing wastewater, a method of adding a magnesium (Mg) salt to phosphorus-containing wastewater and then performing biological treatment has been proposed. In this method, phosphorus in the wastewater is treated with magnesium ammonium phosphate 6. Water salt (MA
The MAP removed as P) and the collected MAP can be effectively reused as a fertilizer containing phosphorus and ammonia.

[0005]

The conventional treatment apparatus shown in FIGS. 5 and 6 can remove phosphorus by excessively ingesting phosphorus in wastewater into activated sludge. It is unstable and has a drawback that phosphorus is released again when surplus sludge is placed in anaerobic conditions such as a sludge thickening tank. Further, in this method, phosphorus removed from wastewater cannot be effectively used as MAP.

On the other hand, in the method of recovering phosphorus as MAP by adding a magnesium salt to wastewater, the phosphorus contained in ordinary wastewater often has a form other than orthophosphoric acid that can be recovered as MAP. In addition, there is a drawback that MAP generation efficiency and recovery efficiency are poor.

[0007] The present invention solves the above-mentioned conventional problems and provides a wastewater treatment apparatus capable of efficiently removing phosphorus and nitrogen in wastewater and efficiently recovering a part of the wastewater as MAP. With the goal.

[0008]

According to a first aspect of the present invention, there is provided a wastewater treatment apparatus comprising: an anaerobic treatment tank; a MAP reaction tank into which the treatment liquid in the anaerobic treatment tank is introduced; A denitrification treatment tank or an aerobic treatment tank.

A wastewater treatment apparatus according to a second aspect of the present invention includes a denitrification treatment tank, a MAP reaction tank into which the treatment liquid in the denitrification treatment tank is introduced, and a nitrification treatment tank into which the treatment liquid in the MAP reaction tank is introduced. It is characterized by comprising.

In the wastewater treatment apparatus of the present invention, wastewater containing phosphorus and nitrogen and sludge returned from a sedimentation tank at the subsequent stage are caused to flow into an anaerobic treatment tank (hereinafter referred to as "anaerobic tank"). Is released to the liquid side. The phosphorus released from the activated sludge to the liquid side has undergone biological treatment and has a high ratio of orthophosphoric acid. Therefore, the MAP reaction tank is introduced with the anaerobic treatment liquid containing wastewater-derived phosphorus and the phosphoric acid having a high ratio of orthophosphoric acid released from the anaerobic tank and ammonia from the wastewater. High MAP generation efficiency.

The treatment liquid in the MAP reaction tank is introduced into a denitrification treatment tank (hereinafter, referred to as a "denitrification tank"), and N in the nitrification circulating liquid is introduced.
O ₃ and NO ₂ are denitrified.

Alternatively, the treatment liquid in the MAP reaction tank is introduced into an aerobic treatment tank (hereinafter, referred to as “aerobic tank”) to remove BOD and, at the same time, excessively ingesting phosphorus under aerobic conditions. Is removed.

In the wastewater treatment apparatus of the present invention, wastewater containing phosphorus and nitrogen and a circulating liquid from a nitrification tank (hereinafter, referred to as "nitrification tank") flow into the denitrification tank to remove nitrogen. Remove.

In this denitrification tank, most of the phosphorus in the wastewater undergoes biological treatment to become orthophosphoric acid. Also,
Most of the organic nitrogen in wastewater also undergoes biological treatment to form ammonia.

Therefore, since the denitrification treatment solution containing orthophosphoric acid and ammonia is introduced into the MAP reaction tank,
High MAP generation efficiency in AP reactor.

The treatment liquid in the MAP reaction tank is subjected to nitrification treatment in a nitrification tank.

As described above, in the wastewater treatment apparatus according to the first and second aspects, phosphorus and nitrogen can be removed.
Since phosphorus in the form of orthophosphoric acid that has undergone biological treatment is introduced into the P reaction tank, phosphorus can be efficiently recovered as MAP. In particular, since the MAP reaction tank is provided downstream of the anaerobic tank or the denitrification tank, the MAP generation efficiency is further improved because phosphorus released from sludge or phosphorus subjected to biological treatment can be immediately converted to MAP. .

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, referring to FIG. 7, an MA suitable for the present invention will be described.
The configuration of the P reaction tank will be described.

The MAP reactor 6 is a reactor having an inlet pipe 11 for water to be treated at a lower part and an outlet pipe 12 for treated water at an upper part, and having an open top. The reaction tank 6 includes a small diameter portion 6A, a large diameter portion 6B, and a large diameter portion 6C.
The granulation reaction part of P, the large diameter part 6C is a precipitation part, and the large diameter part 6B is a transition part. An air diffusion tube 13 is provided below the small diameter portion 6A, and is configured to diffuse air into the reaction tank 6. A lower part of the small diameter portion 6A is provided with a supply pipe 14 for a magnesium salt solution such as MgCl ₂ (as long as it contains a magnesium salt and may be seawater) and an upper part of an alkali agent such as NaOH on the upper part. A supply pipe 19 is provided. Reference numeral 10 denotes MAP particles.

A draft pipe 15 is provided in the large diameter portion 6C, and is configured to guide the exhaust so that the air aerated from the air diffuser 13 does not disturb the liquid in the settling portion. The large-diameter portion 6C is provided with a pipe 16 provided with a pump P for extracting treated water and circulating the treated water to the inlet 2 below the reaction tank 6. Reference numeral 17 denotes an overflow weir, and reference numeral 18 denotes a discharge pipe for a MAP crystal.

In the MAP reactor 6, the pH conditions at which MAP precipitates, ie, pH 7.7 to 9.0, preferably p
NaO through the supply pipe 15 so that H8.3 to 8.5.
An alkali agent such as H is injected. When magnesium is insufficient for MAP precipitation, a magnesium salt solution such as MgCl ₂ is injected from the supply pipe 14.

In the small diameter portion 6A, that is, the MAP granulation reaction portion,
The MAP is granulated by the reaction of phosphorus, ammonia, and magnesium ions in the water to be treated, using the MAP particles 10 already precipitated as seed crystals. That is, the aeration from the air diffuser 13 and the inflow of the water to be treated from the introduction pipe 11 bring the MAP particles 10 into a fluid state, and the surface of the
AP precipitates and large MAP particles are granulated.

In the precipitation of MAP, if the concentration of phosphorus in the water to be treated is excessively high, MAP microcrystals are self-precipitated in the absence of seed crystals, and large MAP particles may not be obtained. As in the MAP reaction tank 6 in FIG. 7, the treatment liquid is extracted from the large diameter portion 6C by the pipe 16 and the pump P and circulated, whereby the phosphorus concentration in the MAP granulation reaction section in the reaction tank 6 can be reduced. . Thereby, the degree of supersaturation of the MAP in the reaction vessel is reduced, and the MAP does not self-precipitate as fine crystals, but only precipitates on the surface of the seed MAP particles 10 to promote the enlargement of the MAP particles. I can do it.

The circulation of the treated water is performed by the MAP in the reaction tank 6.
It is desirable that the concentration of phosphorus in the granulation reaction section be 100 mg / L or less, particularly 40 to 80 mg / L. However, the circulation of this treated water is not essential, and M is used under conditions where sludge flows out but MAP particles do not.
The AP reaction solution may be taken out and the amount of the MAP crystal pulled out may be controlled, whereby the size of the crystal can be controlled.

The liquid whose phosphorus concentration has decreased due to the precipitation of MAP rises in the reaction tank 6 and is discharged from the discharge pipe 12.
At this time, since the MAP particles are large, even when treating the raw water containing a large amount of sludge solid matter,
The particles are well settled out without being discharged together with the solids. That is, since the MAP particles have a specific gravity and a particle size which are sufficiently larger than the sludge solids, they precipitate and separate with good separability, and only the sludge solids are contained in the treated water and overflow the overflow weir 17. Is discharged.

The bubbles 20 generated by the aeration by the air diffuser 13 are guided to the draft tube 15 and separated and exhausted from the liquid without disturbing the liquid in the settling portion of the large diameter portion 6C.

On the other hand, the MAP particles coarsened in the reaction granulation section of the small diameter section 6A are intermittently taken out from the discharge pipe 18 below the reaction tank 6.

Next, an embodiment of the wastewater treatment apparatus of claim 1 will be described with reference to FIGS. In FIGS. 1 to 3 and FIG. 4 to be described later, the configuration of the MAP reaction tank 6 is shown in a simplified manner, and illustration of a part of piping and the like is omitted.

The wastewater treatment apparatus shown in FIG.
It is composed of a reaction tank 6, an aerobic tank 2 and a sedimentation tank 3, and the wastewater is
The sludge is returned to the anaerobic tank 1 together with the sludge returned from the sedimentation tank 3. In the anaerobic tank 1, phosphorus in the returned sludge is released to the liquid side under anaerobic conditions. This anaerobic treatment liquid is introduced into the MAP reaction tank 6.

In the MAP reactor 6, the phosphorus released in the anaerobic tank 1 (this phosphorus has been subjected to biological treatment in the subsequent aerobic tank 2, and most of the phosphorus is positive phosphorus which is advantageous for MAP generation). And phosphorus from wastewater, ammonia from wastewater, Mg compound and MA from wastewater
The Mg compound added to the P reaction tank 6 reacts under the above-mentioned pH condition to generate MAP.

The MAP reaction liquid from which phosphorus and ammonia have been removed by the generation of MAP in the MAP reaction tank 6 is then introduced into the aerobic tank 2 to remove BOD under aeration. Further, in the aerobic tank 2, excessive intake of phosphorus is performed under aerobic conditions, and the phosphorus concentration in the solution is further reduced.

The aerobic treatment liquid is then introduced into the settling tank 3,
Solid-liquid separation is performed, and the separated liquid is discharged out of the system as treated water. This treated water removes phosphorus and nitrogen by the MAP generation in the MAP reaction tank 6 and further removes B by the biological treatment in the aerobic tank 2.
It is a treated water of good water quality from which OD has been removed and phosphorus has been removed.

On the other hand, the separated sludge that has taken in phosphorus in the form of orthophosphoric acid by biological treatment is returned to the anaerobic tank 1 as return sludge.

The wastewater treatment apparatus shown in FIG.
The reactor is composed of a reaction tank 6, a denitrification tank 4, a nitrification tank 5, and a settling tank 3, and wastewater is introduced into the anaerobic tank 1 together with sludge returned from the settling tank 3 at a later stage. In the anaerobic tank 1, under anaerobic conditions, phosphorus in the returned sludge (mostly phosphorus
It is in the form of orthophosphoric acid, which is advantageous for AP formation. ) Is released to the liquid side. This anaerobic treatment liquid is introduced into the MAP reaction tank 6.

In the MAP reactor 6, phosphorus and ammonia are removed by the generation of MAP in the same manner as in the wastewater treatment apparatus shown in FIG.

Next, the MAP reaction solution is introduced into the denitrification tank 4. In the denitrification tank 4, NO ₃ and NO ₂ in the nitrification circulating liquid are denitrified using BOD in the wastewater.

The denitrification treatment liquid is introduced into the nitrification tank 5, and the ammonia in the liquid is oxidized to NO ₃ and NO ₂ by aeration. In addition, phosphorus is taken into activated sludge under aerobic conditions, and the phosphorus concentration in the liquid is reduced.

A part of the nitrification solution is composed of NO ₃ and NO ₂
Is fed back to the denitrification tank 4 and the remainder is sent to the settling tank 3 for solid-liquid separation.

The separated liquid in the settling tank 3 is discharged out of the system as treated water. This treated water is high quality treated water in which phosphorus and nitrogen are removed by MAP generation in the MAP reaction tank 6, nitrogen is removed in the denitrification tank 4, and phosphorus is removed in the nitrification tank.

On the other hand, the separated sludge is returned to the anaerobic tank 1 as return sludge.

The waste water treatment apparatus shown in FIG. 2 is an embodiment in which a high nitrogen removal rate is not required, NO ₃ or NO
_The nitrification solution containing ₂ is subjected to solid-liquid separation in the sedimentation tank 3 as it is to obtain treated water. When a high nitrogen removal rate is required, two denitrification tanks are provided as shown in FIG. Finish denitrification.

The wastewater treatment apparatus shown in FIG.
It is composed of a reaction tank 6, a first denitrification tank 4A, a nitrification tank 5, a second denitrification tank 4B, a re-aeration tank 7, and a sedimentation tank 3. Up to the nitrification tank 5, the same as the wastewater treatment apparatus shown in FIG. The process is performed.

A part of the nitrification treatment liquid in the nitrification tank 5 is returned to the first denitrification tank 4A, and the remainder is introduced to the second denitrification tank 4B. In the second denitrification tank 4B, the concentration of nitrogen in the liquid is reduced by adding methanol or the like to further remove nitrogen. The treatment liquid in the second denitrification tank 4B is again taken up in the re-aeration tank 7 and then solid-liquid separated in the precipitation tank 3 in the same manner as described above.

Next, an embodiment of the wastewater treatment apparatus of claim 2 will be described with reference to FIG.

The wastewater treatment apparatus shown in FIG.
A, a MAP reaction tank 6, a nitrification tank 5, a second denitrification tank 4B, a re-aeration tank 7, and a precipitation tank 3.

The wastewater is mixed with the nitrification circulating liquid from the subsequent nitrification tank 5 and the returned sludge from the sedimentation tank 3 together with the first denitrification tank 4A.
Will be introduced. In the first denitrification tank 4A, under anaerobic conditions, NO ₃ and NO ₂ in the nitrification circulating liquid are utilized by utilizing BOD in wastewater.
Is denitrified. In addition, most of the phosphorus other than phosphoric acid in wastewater undergoes biological treatment to become orthophosphoric acid,
Most of the organic nitrogen in wastewater also undergoes biological treatment to form ammonia.

The denitrification treatment liquid in the first denitrification tank 4A is MAP
Phosphorus and nitrogen are removed by the introduction into the reaction tank 6 and the generation of MAP. In the denitrification treatment liquid in the first denitrification tank 4A, most of phosphorus is present in the form of orthophosphoric acid. In addition, since most of nitrogen is present in the form of ammonia, the efficiency of the MAP generation reaction in the MAP reactor 6 is very high, and the efficiency of removing phosphorus and nitrogen is high. In addition, since the denitrification reaction is also an alkali release reaction, the pH of the denitrification treatment solution slightly increases, and the MAP
It can be easily adjusted to a pH condition suitable for production.

The MAP reaction solution in the MAP reaction tank 6 is sequentially fed to the nitrification tank 5, the second denitrification tank 4B, the re-aeration tank 7 and the precipitation tank 3, and is supplied in the same manner as in the wastewater treatment apparatus shown in FIG. , Processing is performed.

When a high nitrogen removal rate is not required in this wastewater treatment apparatus, the second denitrification tank 4B and the re-aeration tank 7 are omitted, and the nitrification treatment liquid in the nitrification tank 5 is replaced with the one shown in FIG.
As in the case of the wastewater treatment apparatus described above, the liquid may be directly sent to the sedimentation tank 3 to be separated into solid and liquid.

The wastewater treatment apparatus shown in FIGS. 1 to 4 is one embodiment of the wastewater treatment apparatus of the present invention, and the present invention is not limited to the illustrated ones unless it exceeds the gist thereof. .

For example, the MAP reaction tank is not limited to a crystallization tank for taking out MAP crystals as shown in FIG. 7, and a liquid containing fine MAP particles is directly supplied to a subsequent tank. Is also good. Even in this case, the liquid containing fine MAP particles is finally solid-liquid separated in the sedimentation tank, and
AP separation is performed.

[0053]

The present invention will be described more specifically with reference to the following examples.

Example 1 Wastewater having the quality shown in Table 1 was treated by the wastewater treatment apparatus shown in FIG. 3 under the following conditions.

Processing conditions Mg salt added amount in MAP reactor: Magnesium chloride added to P
1.2 times the molar ratio of O ₄ -P pH of the MAP reaction tank: 8.2 to 8.7 Nitrification circulating liquid: 200 m ³ / day Returned sludge: 100 m ³ / day Table 1 shows the water quality and flow rate.

[0056]

[Table 1]

As apparent from Table 1, the total removal rate was 99.4% for T-N, 97.5% for T-P, and 99% for BOD99.
The value was as high as 3%.

Particularly, the phosphorus removal rate in the MAP reactor is high,
MAP crystal (magnesium ammonium phosphate hexahydrate)
Was recovered at 93 kg / day.

Example 2 Wastewater having the quality shown in Table 2 was treated by the wastewater treatment apparatus shown in FIG. 4 under the following conditions.

Processing conditions Mg salt added amount in MAP reactor: Magnesium chloride added to P
1.2 times the molar ratio of O ₄ -P pH of the MAP reaction tank: 8.2 to 8.7 Nitrification circulating liquid: 200 m ³ / day Returned sludge: 100 m ³ / day Table 2 shows the water quality and flow rate.

[0061]

[Table 2]

As is clear from Table 2, the total removal rate was TN 99.4%, TP 87.5%, and BOD99.
The value was as high as 3%.

In particular, the phosphorus removal rate in the MAP reactor is high,
MAP crystal (magnesium ammonium phosphate hexahydrate)
Was recovered at 85 kg / day.

Example 3 Wastewater having the quality shown in Table 3 was treated by the wastewater treatment apparatus shown in FIG. 1 under the following conditions.

Processing conditions Mg salt added amount in MAP reactor: Magnesium chloride added to P
1.2 times the molar ratio of O ₄ -P pH of the MAP reaction tank: 8.2 to 8.7 Returned sludge amount: 100 m ³ / day Table 3 shows the water quality and flow rate of the treatment liquid in each tank.

[0066]

[Table 3]

As is evident from Table 3, the total removal rate was 33.3% for TN, 97.2% for TP and 98% for BOD98.
The value was as high as 0%.

In particular, the phosphorus removal rate in the MAP reactor is high,
MAP crystal (magnesium ammonium phosphate hexahydrate)
Was collected at 83 kg / day.

[0069]

As described above in detail, according to the wastewater treatment apparatus of the present invention, phosphorus and part of nitrogen in wastewater are efficiently recovered as MAP, and the concentration of phosphorus in treated water or the concentration of nitrogen is further reduced. Can be reduced.

In the present invention, an anaerobic tank or a denitrification tank is provided before the MAP reaction tank, and the form of orthophosphoric acid released from sludge under anaerobic conditions or the form of orthophosphoric acid by anaerobic biological treatment is determined. In order to introduce the phosphorous into the MAP reactor,
Compared to the case where wastewater is directly subjected to a MAP reaction, the MAP generation efficiency is high, the phosphorus and nitrogen removal efficiency is high, and treated water of good quality can be obtained.
AP collection efficiency is also improved.

In particular, when a denitrification tank is provided before the MAP reaction tank, nitrogen and phosphorus in the wastewater can be fed to the MAP reaction tank in the form of ammonia and orthophosphoric acid, respectively. It is advantageous for the reaction.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a wastewater treatment apparatus according to claim 1;

FIG. 2 is a system diagram showing another embodiment of the wastewater treatment apparatus according to claim 1;

FIG. 3 is a system diagram showing another embodiment of the wastewater treatment apparatus according to claim 1;

FIG. 4 is a system diagram showing an embodiment of a wastewater treatment apparatus according to claim 2;

FIG. 5 is a system diagram showing a conventional biological dephosphorization treatment device.

FIG. 6 is a system diagram showing a conventional biological dephosphorization and denitrification treatment apparatus.

FIG. 7 is a system diagram showing a configuration of a MAP reaction tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anaerobic tank 2 Aerobic tank 3 Sedimentation tank 4 Denitrification tank 4A 1st denitrification tank 4B 2nd denitrification tank 5 Nitrification tank 6 MAP reaction tank 7 Reaeration tank

Claims (2)

[Claims] 1. An anaerobic treatment tank, a MAP reaction tank into which the treatment liquid in the anaerobic treatment tank is introduced, and a denitrification treatment tank or an aerobic treatment tank into which the treatment liquid in the MAP reaction tank is introduced. A wastewater treatment apparatus, comprising: a wastewater treatment apparatus; 2. A denitrification treatment tank, a MAP reaction tank into which the treatment liquid in the denitrification treatment tank is introduced, and a nitrification treatment tank into which the treatment liquid in the MAP reaction tank is introduced. Wastewater treatment equipment.