JP2013184110A - Device for recovering phosphorus from phosphorus-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for recovering phosphorus from phosphorus-containing water, in which agglomerating phosphorus is not precipitated and a phosphorus recovery rate is not lowered.SOLUTION: A device for recovering phosphorus includes a crystallization reaction tower 2 for recovering phosphorus by a crystallization reaction. An raw water introduction port 17 is arranged in the lower part of the crystallization reaction tower 2, a discharge port 20 of treated water is arranged in the upper part thereof and a pH adjustment tank 3 for adjusting pH is arranged on the outside of the crystallization reaction tower 2. One end of an upper part circulation pipeline 30 is connected to the discharge port 20 of treated water and another end of the upper part circulation pipeline 30 is connected to the pH adjustment tank 3. The pH adjustment tank 3 is connected to the lower part of the crystallization reaction tower 2 by a lower part circulation pipeline 31. While the raw water introduced from the raw water introduction port 17 of the lower part of the crystallization reaction tower 2 is made to ascend inside the crystallization reaction tower 2, phosphorus is recovered therefrom, and then the raw water is sent from the discharge port 20 of treated water in the upper part of the crystallization reaction tower 2 to the pH adjustment tank 3 through the upper part circulation pipeline 30 as circulating water. The treated water after pH adjustment is returned and circulated as circulating water to the lower part of the crystallization reaction tower 2 through the lower part circulation pipeline 31.

Description

  The present invention relates to a phosphorus recovery apparatus for phosphorus-containing water with an improved phosphorus recovery rate.

  Phosphorus is imported and used in large quantities as fertilizers, industrial chemicals, and other raw materials, food, and feed, but it is released into human bodies by excreta, miscellaneous wastewater, industrial wastewater from factories, livestock waste, and emissions from agricultural land. Eutrophication is a problem.

  On the other hand, phosphorus is a resource that is depleted, and it is important to switch from “removing” to “recovering” in order to create a recycling-oriented society.

  As a conventional phosphorus removal method, a biological phosphorus removal method, a simultaneous aggregation method, and a crystallization dephosphorization method are known. The biological phosphorus removal method is based on the principle that the amount of phosphorus withdrawn as excess sludge can be increased as compared with a normal treatment method by making the anaerobic state without aeration of a part of the aeration tank. The simultaneous flocculation method is a method of adding a flocculating agent to an existing aeration tank. The crystallization dephosphorization method is a method that utilizes the crystallization phenomenon of hydroxyapatite (HAP) produced by the reaction of phosphate ions in the liquid with calcium ions and hydroxide ions.

  In the future, the crystallization dephosphorization method will be used effectively from the viewpoint of recovering phosphorus.

  The crystallization and dephosphorization method is disclosed in Patent Document 1, in which crystallization dephosphorization is performed using a porous treatment material having a calcium silicate hydrate as a main constituent and a porosity of 50 to 90% as a dephosphorization material. A method is described. In this method, fine adjustments such as water temperature are not necessary, and the treatment is stable. In addition, there is no inflow of phosphorus-containing water from the sludge treatment, which is a problem in biological phosphorus removal methods, to the water treatment system, and an increase in sludge, which is a problem in the simultaneous coagulation method.

  However, in Patent Document 1, since decarboxylation and calcium addition were not performed, a decrease in the processing speed due to calcium shortage caused by a competitive reaction with calcium carbonate when the phosphorus concentration was low, etc., and could withstand long-term use. I could not.

  Therefore, in Patent Document 2 and Patent Document 3, the raw water is decarboxylated, calcium ions (calcium chloride) are supplied to the raw water or the reaction tank, and the dephosphorization material mainly composed of calcium silicate hydrate is filled. In addition, a technique is shown in which dephosphorization is performed by passing raw water containing phosphorus through a reaction vessel that has been or fluidized. In the crystallization reaction tank, this technique adjusts the pH value of the remaining raw water from 8 to 10 and replenishes calcium ions to dephosphorylate the raw water at high speed.

JP 62-183898 A Japanese Patent No. 3569086 Japanese Patent No. 3766551

  Replenishing calcium ions and adjusting the pH increases the phosphorus removal rate and shortens the treatment time compared to the conventional technique. However, when the phosphorus concentration of the raw water is high, adjusting the pH to 8 or more will increase the seed crystal and phosphorus. Before the reaction, cohesive phosphorus (calcium phosphate) was generated, causing scale problems in each treatment tank. Naturally, the amount of hydroxyapatite deposited on the seed crystal decreases, and the phosphorus recovery rate decreases.

  Further, when dephosphorization is performed from raw water by a crystallization reaction, if the operation of the phosphorus recovery apparatus is continued for a certain period of time, there is a problem that the phosphorus recovery rate decreases due to clogging (that is, SS) or the like. Furthermore, since a part of SS is taken in when phosphorus crystallizes, the purity of hydroxyapatite is also lowered.

  Even if the clogging with SS is prevented by passing the raw water, the reaction time of the seed crystal and the raw water is short, such as the supply water overflows without sufficiently contacting the seed crystal, and it is sufficient for phosphorus precipitation. As a result, the phosphorus recovery rate was reduced.

  Then, this invention makes it a subject to provide the phosphorus collection | recovery apparatus of the phosphorus containing water which eliminates precipitation of cohesive phosphorus and does not reduce a phosphorus collection | recovery rate.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

(Claim 1)
In a phosphorus recovery apparatus equipped with a crystallization reaction tower for charging or flowing phosphorus recovery material inside, using calcium silicate hydrate as a seed crystal, and recovering the phosphorus from raw water containing phosphorus by a crystallization reaction,
A raw water inlet for introducing the raw water containing phosphorus as it is without adjusting the pH is provided at the bottom of the crystallization reaction tower, and an outlet for treated water is provided at the top.
A pH adjustment tank is provided outside the crystallization reaction tower,
One end of an upper circulation pipe is connected to the treated water discharge port, the other end of the upper circulation pipe is connected to the pH adjustment tank, and the lower part of the pH adjustment tank and the crystallization reaction tower is a lower circulation pipe. Connected with
The raw water introduced from the raw water inlet at the bottom of the crystallization reaction tower is recovered in the course of ascending the inside of the crystallization reaction tower, and the treated water discharge port at the top of the crystallization reaction tower. Is sent to the pH adjustment tank as circulating water through the upper circulation pipe, adjusted to a pH of 8.0 to 8.7 in the pH adjustment tank, and the treated water after pH adjustment passes through the lower circulation pipe. Through the lower part of the crystallization reaction tower through the circulating water,
A phosphorus recovery apparatus, wherein the amount of the circulating water is adjusted to be in a range of 3 to 30 times the amount of raw water containing phosphorus introduced from the lower part of the crystallization reaction tower.

(Claim 2)
2. The phosphorus recovery apparatus according to claim 1, wherein a raw water mixed with bubbles is introduced from the lower part of the crystallization reaction tower, which has an aeration nozzle at the lower part of the crystallization reaction tower.

(Claim 3)
The phosphorus recovery apparatus according to claim 1, wherein a treated water discharge pipe is connected to the pH adjustment tank.

(Claim 4)
The raw water supply pipe for supplying raw water provided in the calcium chloride mixing tank has a mixing tank equipped with a calcium chloride addition facility in the preceding stage of the crystallization reaction tower, and is a phosphor for measuring the phosphorus concentration of the raw water. Having a concentration meter, measuring the phosphorus concentration in the phosphorus concentration meter, and depending on the phosphorus concentration of the raw water, calcium (Ca) is 2 to 3 times the weight ratio of phosphorus (P) The phosphorus recovery apparatus according to claim 1, wherein calcium chloride is added to the mixing tank.

(Claim 5)
5. The phosphorus concentration of the raw water in the crystallization reaction tower is 30 mg / l or less in a state diluted with circulating water in the crystallization reaction tower. Phosphorus recovery equipment.

  According to the present invention, a circulation line is formed between the crystallization reaction tower and the pH adjustment tank, and the phosphorus concentration of the crystallization reaction tower is increased by circulating phosphorus-containing raw water or treated water through the circulation line. By maintaining the pH at about 30 mg / l at all times and adjusting the pH in the circulation line, it is possible to eliminate the problem of cohesive phosphorus precipitation.

  In addition, since the treated water is circulated, sufficient contact time or reaction time between the raw water and the seed crystal is secured for phosphorus precipitation, and the recovery efficiency of phosphorus in the waste water is not reduced.

  Furthermore, it has adjusting means for adjusting the amount of circulating water to be in the range of 3 to 30 times, preferably 5 to 25 times the amount of raw water containing phosphorus introduced from the lower part of the crystallization reaction tower. As a result, the number of contact between the raw water and the seed crystal is also increased, the compaction of the seed crystal is prevented, the reaction efficiency is increased, and the recovery efficiency of phosphorus in the raw water can be increased.

  Furthermore, when air is diffused from the lower part of the crystallization reaction tower or bubbles are introduced, SS is pulled out above the tower by the bubbles, so that clogging with SS is prevented, and a decrease in phosphorus recovery rate due to the clogging can be prevented. . For this reason, there is also an effect that there is no need for film treatment for removing SS in the previous stage of the phosphorus recovery apparatus of the present invention.

  In general wastewater treatment, treated water after phosphorus recovery is transferred to a coagulation sedimentation tank or the like, and wastewater treatment is performed. Since the present invention can be used in the coagulation sedimentation tank, SS is not removed, and blockage due to SS is prevented in the phosphorus recovery process, so that a series of general wastewater treatment is taken into consideration. It is considered to have a very desirable form.

It is a schematic diagram which shows the phosphorus collection | recovery apparatus based on one Example of this invention. It is the graph showing the phosphorus collection | recovery rate which concerns on pH, phosphorus concentration, and the amount of circulating water in a crystallization reaction process at the time of processing in the phosphorus collection | recovery apparatus which concerns on one Example of this invention.

  Embodiments of the present invention will be described below.

  The drainage (raw water) for phosphorus recovery in the present invention is not particularly limited as long as it can recover phosphorus, for example, human waste, miscellaneous wastewater, industrial wastewater from factories, livestock waste, discharge from agricultural land, etc. If phosphorus can be recovered from wastewater where eutrophication into the water becomes a problem, phosphorus can be recovered while recovering the problem of eutrophication, which has a double effect.

  FIG. 1 is a view showing an example of the phosphorus recovery apparatus of the present invention.

  In the figure, 1 is a calcium mixing tank, and the mixing tank 1 is provided with a stirrer 10. 11 is a supply pipe for raw water containing phosphorus, and 12 is a calcium chloride supply facility.

  Although not shown, the calcium chloride supply facility 12 includes a calcium chloride tank and, if necessary, a stirrer. The calcium chloride supply facility 12 is provided with a calcium chloride pump 13, and the supply of calcium chloride is controlled by, for example, an electrical signal from a phosphorus concentration meter 14 provided in the raw water supply pipe 11.

  The supply pipe 11 for raw water containing phosphorus may be connected to any part of the mixing tank 1 as long as the raw water containing phosphorus can be supplied from the upper part of the mixing tank 1.

  In the mixing tank 1, calcium ions are supplied from the calcium chloride supply facility 12 to the raw water. In this embodiment, calcium chloride is used because it is preferable that calcium chloride is easily eluted as calcium ions.

  The purpose of adding calcium chloride is to adjust the calcium concentration in the raw water supplied to the crystallization reaction tower 2 disposed in the latter stage of the mixing tank 1 according to the phosphorus concentration of the raw water, and to increase the calcium necessary for the precipitation of hydroxyapatite. This is to supplement the ions.

  The amount of calcium injected into the raw water in the mixing tank 1 is preferably adjusted within a range of 2 to 3 times the weight ratio of calcium (Ca) to phosphorus (P) according to the phosphorus concentration in the raw water.

  In this invention, pH in the mixing tank 1 is 6.5 or more and less than 7.0, and the process which adjusts pH to 7 or more is not performed. This is because the problem of cohesive phosphorus precipitation does not occur.

  The crystallization reaction tower 2 disposed in the rear stage of the mixing tank 1 is formed in a tower shape, and a raw water discharge pipe 15 connected to the lower part of the mixing tank 1 is provided at the lower part of the tower-like crystallization reaction tower 2. The raw water discharge pipe 15 is provided with a raw water pump 16 so that the raw water is introduced from the lower part of the crystallization reaction tower 2 through the raw water inlet 17.

  Reference numeral 20 denotes a treated water discharge port for discharging treated water inside the columnar crystallization reaction tower 2. The treated water discharge port 20 is provided in the upper part of the crystallization reaction tower 2, and when the treated water is discharged from the treated water discharge port 20, the SS accumulated in the upper part of the crystallization reaction tower 2 is also discharged. Therefore, the structure is such that SS is not accumulated in the crystallization reaction tower 2.

  3 is a pH adjusting tank 3 provided adjacent to the tower-like crystallization reaction tower 2. The treated water inside the tower-shaped crystallization reaction tower 2 flows from the treated water discharge port 20 provided at the upper part of the crystallization reaction tower 2 into the pH adjustment tank 3 through the upper circulation pipe 30. Composed. The circulating water whose pH is adjusted in the pH adjusting tank 3 is configured to be returned to the lower part of the tower-like crystallization reaction tower 2 through the lower circulating pipe 31. 32 is a circulation pump. The lower circulation pipe 31 is provided with a valve 33 so that the amount of circulating water returned to the lower part of the crystallization reaction tower 2 can be adjusted. In the present embodiment, the upper circulation pipe 30 and the lower circulation pipe 31 constitute a circulation line.

  The inside of the crystallization reaction tower 2 is filled with a dephosphorization material mainly composed of calcium silicate hydrate so as to be flowable. The stack height of the seed crystals is preferably in the range of 1000 mm to 3000 mm.

  Examples of the calcium silicate hydrate include, for example, one kind or a combination of two or more kinds of fine plate-like crystals, columnar crystals, and acicular crystals of tobermorite, zonotrite, hireblandite, and wollastonite. it can.

  In the present embodiment, adopting a structure in which the gas can be diffused from below the crystallization reaction tower 2 promotes the mixing of calcium chloride in the raw water by the air supply in the raw water discharge pipe 15, and further the crystallization reaction tower 2 as it is. It is preferable from the viewpoint that it can be used as air for stirring in the tank from the lower part. Alternatively, a static mixer 22 or the like may be attached to the raw water discharge pipe 15 to promote the mixing of calcium chloride.

  The structure that can be diffused is not particularly limited. For example, an air supply device 21 such as a compressor is provided, compressed air is supplied from the air supply device 21 to the raw water discharge pipe 15, and air is mixed into the raw water. It is preferable to supply from below the crystallization reaction tower 2.

  The treated water inside the crystallization reaction tower 2 returns to the pH adjustment tank 3 from the upper part of the crystallization reaction tower 2 via the upper circulation pipe 30 and the pH is adjusted. If necessary, a stirrer 37 may be installed in the pH adjusting tank 3. The pH adjusting tank 3 includes a sodium hydroxide supply facility 34 and a pH sensor 35. The sodium hydroxide supply facility 34 includes a sodium hydroxide tank (not shown), and a stirrer in the tank as necessary. The sodium hydroxide supply facility 34 is provided with a sodium hydroxide pump 36, and the supply of sodium hydroxide is controlled by, for example, an electric signal from the pH sensor 35. In the pH adjusting tank 3, the pH is adjusted to a range of 8.0 to 8.7 by adding sodium hydroxide.

  In this embodiment, sodium hydroxide is used because it is preferable that it is easy to elute as hydroxide ions.

  In the pH adjustment tank 3, when it is confirmed that phosphorus is removed to a phosphorus concentration of 30 mg / l or less, preferably 25 mg / l or less, more preferably 20 mg / l or less, a part of the treated water is a pH adjustment tank. 3 is discharged from the upper part through the treated water discharge pipe 38 and transferred to the next wastewater treatment process. Other treated water is fed from the lower part of the crystallization reaction tower 2 through the lower circulation pipe 31 and circulated. The amount of the circulating water flowing into the crystallization reaction tower 2 is adjusted by a valve 33 installed in the lower circulation pipe 31.

  The SS discharged from the crystallization reaction tower 2 is also discharged from the treated water discharge pipe 38. The reason why SS is not removed in this phosphorus recovery process is that wastewater treatment such as coagulation and precipitation is expected after the phosphorus recovery process, and it is possible to use SS as it is in the coagulation sedimentation tank. This is because it is a preferred embodiment.

  In addition, a HAP discharge pipe 40 is provided at the lower portion of the crystallization reaction tower 2 to recover the seed crystal HAP after reacting with phosphorus, and the valve 41 is opened after the seed crystal has sufficiently reacted with phosphorus. To recover HAP.

  Examples of the present invention will be described. The present invention is not limited to the embodiments.

<Test equipment>
The apparatus shown in FIG. 1 was used.
The tower-shaped crystallization reaction tower 2 had a tower diameter of 0.147 m, a tower cross-sectional area of 0.017 m ² , a seed crystal height of 1.8 m, and a raw water supply amount of 1.1 m ³ / D.

The following test data in the present invention was conducted using human waste. The properties of the raw water were generally pH 6.5 to 7.1, PO ₄ -P 45 to 55 mg / l, SS 10 to 50 mg / l, and temperature 28 to 33 ° C.

  In mixing tank 1, calcium ions were added, and the calcium ion concentration of raw water was adjusted to 2 to 3 times the phosphorus concentration of raw water. The pH was about 6.6. Moreover, in the present Example, potassium phosphate was added in the mixing tank 1, and the phosphorus concentration was adjusted to 95-105 mg / l.

  The amount of air inserted in the line flowing from the mixing tank 1 into the crystallization reaction tower 2 was set to 4 to 10 L / min. The amount of air inserted is appropriately adjusted depending on the amount of SS and the compaction state of the seed crystal.

  In the crystallization reaction tower 2, 35 kg of a dephosphorization material mainly composed of calcium silicate hydrate was packed. The LV in the crystallization reaction tower 2 was set to 0.3 m / min or more. The flow rate can be changed as appropriate according to the state of SS and seed crystals.

The discharge amount from the crystallization reaction tower 2 to the pH adjusting tank 3 was 5.1 to 24.1 m ³ / D. In the pH adjusting layer 3, since the phosphorus concentration in the crystallization reaction tower 2 is high when the phosphorus recovery apparatus is started up, the pH is gradually raised to the extent that coherent phosphorus is not generated, and finally the pH is 8.0 to 8. 7 to stabilize.

treated water discharged from the pH adjustment vessel 3 1.1 m ³ / D, circulation to the crystallization reaction circulation line was 4~23m ³ / D.

  In the above state, the result of processing under the conditions of the first embodiment is as shown in FIG.

  By providing a crystallization reaction circulation line when dephosphorizing in the crystallization reaction tower 2, the phosphorus concentration in the crystallization reaction tower 2 is maintained at about 30 mg / L, and the pH is adjusted in the crystallization reaction circulation line. By adjusting to 8.0 to 8.7, precipitation of cohesive phosphorus did not occur.

  Moreover, due to the aeration and flow rate from the lower part of the crystallization reaction tower, the seed crystal was not consolidated in the crystallization reaction tower and the seed crystal was not blocked by SS. In addition, it can be considered that by circulating the treated water in the circulation line, the number of contact times of phosphorus and the seed crystal is increased, and sufficient contact reaction time for HAP precipitation is secured.

  Furthermore, the concentration of SS in the raw water flowing into the phosphorus recovery apparatus of the present invention and the concentration of SS discharged from the treated water discharge pipe are kept at the same level, preventing concentration and accumulation of SS in the crystallization reaction tower. It has been confirmed that.

And according to FIG. 2, in the range of the circulation amount of 4-23 m < ³ > / D in a crystallization reaction process, it turns out that phosphorus recovery rate is 73% or more stably.

  Considering the phosphorus recovery rate and the cost of power for circulating the treated water to the crystallization reaction tower, it is considered preferable to set the circulation rate as low as possible. It has been proved that the phosphorus recovery rate can be stably maintained at 73% or more by adjusting in the range of 3 to 30 times the amount of raw water contained.

  Moreover, when the phosphorus concentration of phosphorus-containing water is in the range of 95 mg / L to 125 mg / L, phosphorus can be recovered to a phosphorus concentration of 30 mg / L or less by using the present invention.

1: Mixing tank 2: Crystallization reaction tower 3: pH adjusting tank 10: Stirrer 11: Raw water supply pipe 12: Calcium chloride supply equipment 13: Calcium chloride pump 14: Phosphorus concentration meter 15: Raw water discharge pipe 16: Raw water pump 17: Raw water inlet 20: treated water outlet 21: air feeder 22: static mixer 30: upper circulation pipe 31: lower circulation pipe 32: circulation pump 33: valve 34: sodium hydroxide supply equipment 35: pH sensor 36: water Sodium oxide pump 37: Stirrer 38: Treated water discharge pipe 40: HAP discharge pipe 41: Valve

Claims (5)

In a phosphorus recovery apparatus equipped with a crystallization reaction tower for charging or flowing phosphorus recovery material inside, using calcium silicate hydrate as a seed crystal, and recovering the phosphorus from raw water containing phosphorus by a crystallization reaction,
A raw water inlet for introducing the raw water containing phosphorus as it is without adjusting the pH is provided at the bottom of the crystallization reaction tower, and an outlet for treated water is provided at the top.
A pH adjustment tank is provided outside the crystallization reaction tower,
One end of an upper circulation pipe is connected to the treated water discharge port, the other end of the upper circulation pipe is connected to the pH adjustment tank, and the lower part of the pH adjustment tank and the crystallization reaction tower is a lower circulation pipe. Connected with
The raw water introduced from the raw water inlet at the bottom of the crystallization reaction tower is recovered in the course of ascending the inside of the crystallization reaction tower, and the treated water discharge port at the top of the crystallization reaction tower. Is sent to the pH adjustment tank as circulating water through the upper circulation pipe, adjusted to a pH of 8.0 to 8.7 in the pH adjustment tank, and the treated water after pH adjustment passes through the lower circulation pipe. Through the lower part of the crystallization reaction tower through the circulating water,
A phosphorus recovery apparatus, wherein the amount of the circulating water is adjusted to be in a range of 3 to 30 times the amount of raw water containing phosphorus introduced from the lower part of the crystallization reaction tower.   2. The phosphorus recovery apparatus according to claim 1, wherein a raw water mixed with bubbles is introduced from the lower part of the crystallization reaction tower, which has an aeration nozzle at the lower part of the crystallization reaction tower.   The phosphorus recovery apparatus according to claim 1, wherein a treated water discharge pipe is connected to the pH adjustment tank.   The raw water supply pipe for supplying raw water provided in the calcium chloride mixing tank has a mixing tank equipped with a calcium chloride addition facility in the preceding stage of the crystallization reaction tower, and is a phosphor for measuring the phosphorus concentration of the raw water. Having a concentration meter, measuring the phosphorus concentration in the phosphorus concentration meter, and depending on the phosphorus concentration of the raw water, calcium (Ca) is 2 to 3 times the weight ratio of phosphorus (P) The phosphorus recovery apparatus according to claim 1, wherein calcium chloride is added to the mixing tank.   5. The phosphorus concentration of the raw water in the crystallization reaction tower is 30 mg / l or less in a state diluted with circulating water in the crystallization reaction tower. Phosphorus recovery equipment.

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