JP3479566B2 - Phosphorus recovery device using seawater - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphorus recovery device using seawater for separating and recovering phosphorus contained in a sewage treatment process using magnesium in seawater.

[0002]

2. Description of the Related Art Sewage sewage treatment is partially performed as an advanced treatment by an anaerobic aerobic method in which microorganisms take up phosphorus in the aerobic part in the aeration tank more than phosphorus is exhaled in the anaerobic part. In the treatment process, sewage passes through the sewer pipe and is first sent to the sand basin 100 as shown in FIG. 4 to remove dust, sediment, and the like. The sewage is then first sent to the settling basin 102, where small dirt in the sewage sinks to the bottom and is removed while flowing. The sewage from which small filth has been removed is sent to the aerobic aeration tank 104, activated sludge containing a large amount of microorganisms is added, and air is blown into the effluent so that the organic matter in the sewage that has not settled in the settling basin 102 is activated. It decomposes with microorganisms and makes it easier to sink. Furthermore, phosphorus contained in sewage is incorporated into microorganisms. This sewage is sent to the final settling basin 106, the sludge mass sinks to the bottom, and the cleaned water is sent to the disinfection basin 108, sterilized with chlorine, and then discharged to the sea or river. A part of the sludge generated in the final settling tank 106 is sent back to the aeration tank 104 as return sludge, and the rest is sent to the flotation concentration tank 110 as surplus sludge to be floated and concentrated, and the sludge is sent to the anaerobic digestion tank 112. To be First settling tank 102
The sludge generated in 1 is sent to the gravity thickening tank 114, gravity-concentrated and the sludge is sent to the digestion tank 112. The sludge sent to the digestion tank 112 is anaerobically digested and decomposed into gas and digested sludge, and then sent to the dehydrator 116 to be converted into sludge cake for landfill processing. Then, the separated liquid generated in the gravity concentration tank 114, the floating concentration tank 110, the dehydrator 116 and the digestion tank 112 is sent to the sand basin 100 again. This was repeated to treat the sewage.

[0003]

However, in the anaerobic aerobic method, excess sludge containing a large amount of microorganisms contains a large amount of phosphorus, and when the excess sludge is anaerobically digested in the digestion tank 112, the microorganisms release phosphorus. Phosphorus elutes in the desorbed liquid. And when the desorbed liquid is not discharged (it is hardly discharged at the sewage treatment plant in Kitakyushu City), the dehydrator 116 is used.
After dehydration in (1), it is returned to the sand basin 100 again as a dehydrated separated liquid containing a large amount of phosphorus. Then, a part of phosphorus reacts with magnesium contained in a small amount in the dehydrated separated liquid (PO ₄ ^{3-
_{+ NH 4 + + Mg 2+ +}} 6H 2 O = MgNH 4 PO 4 · 6
H ₂ O) Magnesium ammonium phosphate (hereinafter, MA
There is a problem in that crystals (referred to as “P”) are generated, and the crystals adhere to the inside of the pipe, and the pipe is clogged. Further, there is a problem that the phosphorus concentration becomes high due to the repetition of the above steps, which becomes a factor of increasing the phosphorus load in the wastewater treatment. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a phosphorus recovery apparatus using seawater that can easily and continuously recover phosphorus contained in a dehydrated separated liquid.

[0004]

A method according to the above-mentioned object.
In the phosphorus recovery apparatus using seawater described above, a first supply port for introducing a treatment liquid containing phosphorus and ammonia and a second supply port for introducing seawater are formed in the lower portion, and the lower end is open. An inner tower and an outer tower, which is arranged outside the inner tower with a gap, has a sediment reservoir in the lower portion, and has an outlet for the treated liquid in the upper portion, and the inner tower A diffusing means is provided in the lower part of the inside of the with a gap. A phosphorus recovery apparatus using seawater according to a second aspect is the phosphorus recovery apparatus using seawater according to the first aspect, wherein the air diffusing means is arranged substantially on the axial center of the inner tower. . The phosphorus recovery apparatus using seawater according to claim 3 is the phosphorus recovery apparatus using seawater according to claim 1 or 2, wherein a diameter expansion portion is provided at an upper portion of the outer tower via a taper portion, The drainage port is provided on one side of the expanded diameter portion, and a baffle plate is provided in front of the drainage port.
The phosphorus recovery device using seawater according to claim 4 is the claim 1.
The phosphorus recovery device using seawater according to any one of items 1 to 3, wherein the treatment liquid is a dehydrated separated liquid of digested sludge. The phosphorus recovery device using seawater according to claim 5 is the phosphorus recovery device using seawater according to any one of claims 1 to 4, wherein the inner tower is provided with an inlet for a pH adjusting liquid. Is configured.

[0005]

In the phosphorus recovery apparatus using seawater according to any one of claims 1 to 5, a first supply port for introducing a treatment liquid containing phosphorus and ammonia and a second supply port for introducing seawater are provided in a lower portion of the inner tower. Are formed, the lower end is open, the outer tower is arranged with a gap outside the inner tower, and the aeration means is provided with a gap inside the inner tower with a gap. When a treatment liquid containing phosphorus and ammonia is introduced from the first supply port at the bottom of the inner tower and seawater is introduced as a magnesium source from the second supply port, decarbonation is performed by the aeration means and at the same time phosphorus and ammonia are introduced. React with magnesium to form small crystals of MAP. The treatment liquid containing crystals of small MAP is moved upward by the air diffusing means on the lower side, and the unreacted treatment liquid reacts by adjusting the pH of the upper portion to generate crystals of small MAP. The treated liquid containing the small crystals is sent upward and discharged from the upper part of the inner column to the inner part of the outer column. The discharged small crystals move downward, enter the inner column again through the opening at the lower end of the inner column, and move upward. During this movement, newly generated crystals adhere to the small crystals to form large particles. While repeating such circulation, when the self-weight of the particles becomes larger than the force to be circulated by the aeration means in the inner tower, the particles fall from the opening at the lower end of the inner tower, Accumulates in the reservoir. Therefore, the size of the falling particles can be adjusted by adjusting the strength of the air diffuser. Then, a part of the treated liquid discharged from the upper part of the inner tower is discharged from the liquid discharge port on the upper part of the outer tower.

Particularly, in the phosphorus recovery apparatus using seawater according to claim 2, since the air diffuser is arranged substantially on the axial center of the inner tower, a gap between the inner tower and the air diffuser is formed. Becomes uniform, and the enlarged particles fall from the space between the inner tower and the aeration means without accumulating. In the phosphorus recovery apparatus using seawater according to claim 3, since a diameter-expanded portion is provided in the upper portion of the outer tower via a taper portion, the phosphorus is discharged from the upper portion of the inner tower to the diameter-expanded portion of the outer tower. The generated small crystals move at a lower speed along the tapered portion because the flow speed becomes slower.
And the drainage port is provided on one side of the expanded diameter portion,
Since the baffle plate is provided in front of the drainage port, the crystals are blocked by the baffle plate and fall, and only the treated liquid is discharged from the drainage port. In the phosphorus recovery apparatus using seawater according to claim 4, since the treated liquid is a dehydrated separated liquid of digested sludge, a large amount of phosphorus is contained, and therefore phosphorus is efficiently separated and recovered. In the phosphorus recovery apparatus using seawater according to claim 5, since an inlet for the pH adjusting liquid is provided in the inner tower, an alkaline agent for adjusting the pH is appropriately supplied from the inlet to accelerate the reaction. Can be made.

[0007]

Embodiments of the present invention will now be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 1 is a schematic explanatory view of a phosphorus recovery apparatus using seawater according to an embodiment of the present invention, FIG. 2 is a flow chart of phosphorus recovery, and FIG. 3 shows a relationship between a reaction pH of a treatment liquid and a phosphorus removal rate. It is a graph showing.

In a phosphorus recovery apparatus 10 using seawater according to an embodiment of the present invention shown in FIG. 1, an outer tower 14 is arranged outside the inner tower 12 with a gap, and a lower inner part of the inner tower 12 is arranged. The air diffuser 16 is provided. These will be described in detail below. The inner tower 12 is formed with a first supply port 18 for introducing a treatment liquid containing phosphorus and ammonia and a second supply port 19 for introducing seawater in the lower part, and has a lower end opened, and an upper part. A plurality of slit-shaped openings 20
Are formed. Then, the treatment liquid treated in the dehydrated separated liquid pit 24, the precipitation tank 26, and the storage tank 28 is injected into the inner tower 12 from the first supply port 18, and the seawater in the seawater tank 30 is supplied from the second supply port 19. It is designed to be introduced into the inner tower 12. Further, an alkali tank 32 is provided, and caustic soda, which is an example of a pH adjusting liquid, is appropriately supplied from the upper portion of the inner tower 12 so that the pH value falls within a predetermined range. In this case, the inner tower 12 may be provided with an inlet for this pH adjusting liquid. The outer tower 14 is provided with a storage portion 33 for large MAP particles 48 in the lower portion, and a discharge port 35 is provided in the lower portion of the storage portion 33. Further, an enlarged diameter portion 36 is provided on the upper portion of the outer tower 14 via a tapered portion 34.
The drainage port 22 is provided on one side of the expanded diameter portion 36,
A baffle plate 38 is provided in front of the drainage port 22 so as to prevent the MAP crystal 46 from flowing out of the drainage port 22.

In the air diffuser 16, a bubble generating plate 40 is formed in a gap 42 in the lower inner part of the inner tower 12 in alignment with the axis of the inner tower 12.
The air pump 44 sends air to generate many bubbles in the inner tower 12. By generating bubbles in the inner tower 12 as described above, the treatment liquid in the inner tower 12 is decarbonated and stirred to facilitate reaction between phosphorus in the treatment liquid and magnesium in seawater. In addition, small M generated in the processing solution and reaction
AP crystals 46 and the like are sent upward, and phosphorus in the unreacted treatment liquid reacts with magnesium in seawater by adjusting the pH with an alkaline agent to produce small MAP crystals 46. Further, the treated liquid or the like containing the small MAP crystals 46 is sent upward and flows from the opening 20 in the upper part of the inner column 12 to the expanded diameter part 36 of the outer column 14. Then, the small MAP crystals 46 fall downward along the expanded diameter portion 36 and the taper portion 34 of the outer tower 14, and again from the gap 42 at the lower end of the inner tower 12 to the inner tower 1 again.
Circulate within 2. In the inner tower 12, the MAP crystals 46 newly attach to the small MAP crystals 46 to form particles 48. M more than the force to move the MAP particle 48 upward
When the weight of the AP particles 48 becomes larger, the MAP particles 48 fall from the gap 42 at the lower end of the inner tower 12 and fall out of the outer tower 1.
It collects in the storage part 33 of No. 4. MAP accumulated in the reservoir 33
Particles 48 are taken out from the discharge port 35, and a part of the processed liquid is discharged from the discharge port 22.

A phosphorus recovery apparatus 10 using this seawater is shown in FIG.
As shown in, the case where the dehydrator 116 is used by being connected to the dehydrated separated liquid side will be described. As shown in Table 1, the dehydrated separated liquid had a PH of 8.1, the total phosphorus amount was 50 mg / liter, and the PO ₄ ^3- phosphorus contained therein was 48 mg.
It accounts for 96% in mg / liter. Further, magnesium is contained at 9.3 mg / liter and NH ₄ ⁺ nitrogen is contained at 450 mg / liter.

[0011]

[Table 1]

[0012] Here, the phosphorus removal rate is examined by changing PH. In this experiment, the Mg / P molar ratio was set to 1.5,
Within the range of pH 8.0 to 10.0, PO ₄ ^3- + NH ₄ ⁺ +
When the phosphorus removal rate was investigated by causing a reaction of Mg ²⁺ + 6H ₂ O = MgNH ₄ PO ₄ .6H ₂ O, as shown in Table 2 and FIG. 3, the phosphorus removal rate increased as PH increased, Especially when PH is 9.0 to 10.0, 94 or 95%
Shows high removal rate, but if PH is large, MAP crystals 4
Since 6 was small, it was concluded that PH is preferably performed in the range of 8.2 to 8.5.

[0013]

[Table 2]

As the solution containing magnesium to be reacted with phosphorus, seawater around the sewage treatment plant A is used. As shown in Table 3, Mg ²⁺ has a typical composition of 12
1250 mg / slightly less than 71 mg / l
Contains liters.

[0015]

[Table 3]

First, the dehydrated separated liquid is placed in the dehydrated separated liquid pit 2.
4, after treatment in the settling tank 26 and the storage tank 28, the inner tower 12
1.2 liter / min is injected from the first supply port 18 of the seawater, and at the same time, the seawater in the seawater tank 30 is injected into the second lower part of the inner tower 12.
50-70 ml / min is introduced from the supply port 19 of. Further, at the same time, 9.0 liter / min of air is sent to the bubble generating plate 40, and a caustic soda for pH adjustment is appropriately added so that the reaction pH of the treatment liquid from the upper part of the inner column 12 becomes 8.2 to 8.5. Supply. In the inner tower 12, the dehydrated separated liquid is decarbonated by bubbles and is stirred to react phosphoric acid and ammonia in the treated liquid with magnesium in seawater (PO ₄ ³ + NH ₄ ⁺ + Mg ^{2). +} + 6H ₂ O =
MgNH ₄ PO ₄ .6H ₂ O) is promoted. As a result, small MAP crystals 46 are formed. While sending the dehydrated separated liquid and the small MAP crystals 46 and the like upward, the unreacted treatment liquid is reacted by adjusting the pH to crystallize MAP. Then, the treated liquid obtained by treating the dehydrated separated liquid, seawater,
The small MAP crystals 46, etc. are in the opening 2 in the upper part of the inner tower 12.
It overflows from 0 and flows into the expanded diameter portion 36 of the outer tower 14. The MAP crystals 46 flow downward along the taper portion 34 and the inner tower 1
Circulation is carried out again through the gap 42 at the lower end of 2 into the inner tower 12. In the inner tower 12, the MAP crystal 46 newly attaches to the small MAP crystal 46 to form particles 48. And
MAP particle 48 rather than the force that moves particle 48 upward
When the self-weight of the MAP becomes larger, the MAP particles 48 become
2 falls from the gap 42 at the lower end of the storage tower 33 of the outer tower 14
Accumulate in. The MAP particles 48 accumulated in the reservoir 33 are taken out from the outlet 35. Then, a part of the treated liquid or the like is discharged from the liquid discharge port 22 of the outer tower 14 and sent to the sand basin 100. By doing this, you can easily and continuously
Moreover, phosphorus can be recovered with a high removal rate. Therefore, the MAP crystal does not adhere to the inside of the pipe and block the pipe unlike the conventional case.

In the above embodiment, the air diffuser 16
Although the amount of air supplied is described, the amount of the MAP particles 48 falling may be changed by adjusting this amount. Although caustic soda was used as the pH adjusting liquid in the above-mentioned examples, other alkaline solutions such as potassium hydroxide may be used. Although the bubble generating plate 40 is used as the air diffuser 16 in the above-described embodiment, the bubbles may be generated by using a plurality of pipes.

[0018]

In the phosphorus recovery apparatus using seawater according to claims 1 to 5, a first supply port for introducing a treatment liquid containing phosphorus and ammonia and a second supply for introducing seawater are provided in the lower part of the inner tower. Mouth is formed, the lower end is open, the outer tower is arranged outside the inner tower with a gap, the lower part has a storage part, and the aeration means is the inner lower part of the inner tower. Since phosphorus is provided in the processing liquid, it is possible to continuously separate and collect phosphorus in the processing liquid as large particles. Further, the size of the particles to be collected can be adjusted by changing the amount of air in the air diffuser. Particularly, in the phosphorus recovery apparatus using seawater according to claim 2, since the aeration means is arranged substantially on the axial center of the inner tower, the treatment liquid is circulated between the inner tower and the outer tower. After forming crystals by growing crystals, large particles can be dropped uniformly. The phosphorus recovery apparatus using seawater according to claim 3, wherein an enlarged diameter portion is provided at an upper portion of the outer tower via a tapered portion, and the drainage port is provided on one side portion of the enlarged diameter portion, Since the baffle plate is provided in front of the drainage port, it is possible to circulate the crystals and discharge only the treated liquid and the like from the drainage port. Claim 4
In the phosphorus recovery apparatus using seawater described above, since the treatment liquid is a dehydrated separated liquid of digested sludge, phosphorus can be efficiently recovered. In the phosphorus recovery apparatus using seawater according to the fifth aspect, since the inlet for the PH adjusting liquid is provided in the inner tower, the reaction can be promoted and a large amount of MAP crystals can be generated.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a phosphorus recovery device using seawater according to an embodiment of the present invention.

FIG. 2 is a flow chart of phosphorus recovery.

FIG. 3 is a graph showing the relationship between the reaction pH of the treatment liquid and the phosphorus removal rate.

FIG. 4 is a flow chart of wastewater treatment according to a conventional example.

[Explanation of symbols]

10 Phosphorus recovery device using seawater 12 inner tower 14 outer tower 16 Air diffuser 18 First supply port 19 Second supply port 20 openings 22 Drainage port 24 Dewatered separation pit 26 Settling tank 28 Storage tank 30 seawater tank 32 alkaline tank 33 Storage 34 Tapered part 35 outlet 36 Expanded part 38 Baffle 40 Bubble generator 42 gap 44 air pump 46 crystals 48 particles

Continuation of front page (56) Reference JP-A-4-141293 (JP, A) JP-A-56-84689 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C01B 25 / 00-25/46

Claims (5)

(57) [Claims] 1. An inner tower having a first supply port for introducing a treatment liquid containing phosphorus and ammonia and a second supply port for introducing seawater formed at a lower part thereof, the lower end being open, and It is arranged with a gap on the outside of the tower, has a reservoir for sediment in the lower part, has an outer tower with a drain for the treated liquid in the upper part, and has a gap in the lower part inside the inner tower. An apparatus for recovering phosphorus using seawater, characterized in that the air diffusion means is provided. 2. The phosphorus recovery apparatus using seawater according to claim 1, wherein the air diffuser is arranged substantially on the axial center of the inner tower. 3. An enlarged diameter portion is provided on the upper part of the outer tower via a tapered portion, the drainage port is provided on one side of the enlarged diameter portion, and an obstruction is provided in front of the drainage port. The phosphorus recovery device using seawater according to claim 1 or 2, wherein a plate is provided. 4. The phosphorus recovery apparatus using seawater according to claim 1, wherein the treatment liquid is a dehydrated separated liquid of digested sludge. 5. The phosphorus recovery apparatus using seawater according to claim 1, wherein the inner tower is provided with an inlet for a pH adjusting liquid.