JP2003039081A - Phosphorus recovery apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phosphorus recovery apparatus equipped with a means for recovering ammonium magnesium phosphate of high quality as a useful substance from water to be treated such as sewage or the like. SOLUTION: The phosphorus recovery apparatus is equipped with a means constituted so that an anode 8 and a cathode 9 are immersed in an electrolytic treatment vessel 7 through an anion exchange membrane 10 and water to be treated containing a phosphorus component is introduced into the partition chamber between the anion exchange membrane 10 and the cathode 9 and a current is applied across both electrodes 8 and 9 to electrolytically treat water to be treated and further equipped with a phosphorus crystallization reaction tank 16 (not shown in the drawing) for subjecting the concentrated liquid on the side of the anode 8 to phosphorus crystallization reaction in an alkaline pH region and recovers the phosphorus component in water to be treated as particles of magnesium ammonium phosphate by phosphorus crystallization reaction. Ammonium magnesium phosphate of high quality containing no heavy metals can be recovered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphorus recovery apparatus for recovering phosphorus from water to be treated, and in particular, phosphorus recovery for recovering soluble phosphate ions in wastewater such as sewage as a granular material by crystallization reaction. Regarding the device.

[0002]

2. Description of the Related Art In recent years, along with the progress of eutrophication in rivers, lakes and marshes, it has been required to reduce the discharge of nutrient salts such as nitrogen and phosphorus, which are factors of algae growth, as much as possible. In order to reduce the load on the aquatic environment, it is desirable to remove these nutrient salts at the same time.

Since algae that fix nitrogen exist in water, phosphorus is a limiting factor for algae, and phosphorus removal is more important than nitrogen.

Phosphorus is mainly used as a fertilizer. In terms of resources, the amount of phosphate rock used as a raw material is limited, and it is said that it will be exhausted in about 50 years worldwide.

Therefore, it is important not only to remove phosphorus from various wastewaters including sewage, but also to recover phosphorus as a useful substance.

[0006] Generally, as a method for removing phosphorus, a coagulation-precipitation method and a biological dephosphorization method are known. In either method, it is difficult to recover phosphorus as a useful substance.

However, recently, for example, "environmental technology" (vo
l.27 No. 6 pp397-pp402 pp403-pp411 1998), etc., a phosphorus recovery method utilizing a crystallization reaction as a method for recovering phosphorus from wastewater containing phosphorus components such as sewage as a useful substance. Is proposed.

This method is used in the alkaline region, for example,
For example, phosphate ion in sewage (HPO _Four ^2-) And Ammoniu
Muion (NH_Four ⁺) And magnesium ion (Mg²⁺)When
Is treated by the crystallization reaction of formula (1) to give ammonium phosphate.
Magnesium Ammonium Phosphate:
It is recovered in the form of granules as MAP). Nitrogen, phosphorus
The recovered MAP containing it can be effectively used as a fertilizer.

Mg ²⁺ + NH ₄ ⁺ + HPO ₄ ^{2 −} + OH ⁻ + 6H ² O → Mg (NH ₄ ) PO ₄ . 6H ₂ O (1) In the phosphorus recovery method utilizing this phosphorus crystallization reaction, in order to produce MAP as useful substances from the water to be treated, stable high recovery rate and high quality phosphorus at low cost can be obtained. Collection is required.

[0010]

When the phosphorus component contained in the water to be treated is recovered as MAP by the crystallization reaction, H 2 and H 2
If harmful heavy metals such as g and Cd are contained, these may remain in the recovered MAP. Even if MAP is recovered, unless the heavy metals in MAP satisfy the standard values such as the Fertilizer Control Law, the quality as fertilizer cannot be maintained and it cannot be used as a useful product. Further, in the phosphorus crystallization reaction, when the phosphorus concentration in the water to be treated is low, the phosphorus recovery rate is lowered, and the quality of the recovered MAP is affected depending on the water quality of the water to be treated.

On the other hand, in the phosphorus crystallization reaction, the MAP
Each ion of the produced component reacts equimolar to produce MAP. Therefore, when the concentration of soluble magnesium in the liquid to be treated such as sewage becomes lower than the concentration of phosphorus, the phosphorus recovery rate decreases as shown in FIG. FIG. 8 is a characteristic diagram showing the relationship between the magnesium addition rate and the phosphorus recovery rate. If the magnesium concentration in the water to be treated varies, a stable high phosphorus recovery rate cannot be obtained. As a countermeasure, for example, magnesium chloride (MgCl ₂ ) or magnesium hydroxide
It is necessary to add a chemical such as (Mg (OH) ₂ ). That much
The cost required for MAP collection increases.

The reaction of MAP formation is based on the hydroxide ion (OH ⁻ )
The reaction proceeds well in the vicinity of pH 9 in the alkaline range, and the phosphorus recovery rate increases.

When the pH of the water to be treated is low, the production of MAP is not promoted, and as shown in FIG. 9, the phosphorus recovery rate is lowered when the pH is lowered. FIG. 9 is a characteristic diagram showing the relationship between pH and phosphorus recovery rate. For example, p of sewage to be treated water
Since H is around 7.5, it is necessary to add an alkaline agent such as sodium hydroxide (NaOH) in order to maintain the pH range where the phosphorus recovery rate is high, which increases the MAP production cost.

Further, the phosphorus recovery rate is also affected by the ammonium ion concentration in the water to be treated, and as shown in FIG. 10, when the ammonium ion concentration decreases, the phosphorus recovery rate also decreases. FIG. 10 is a characteristic diagram showing the relationship between ammonium ion concentration and phosphorus recovery rate.

As described above, in the conventional phosphorus recovery method, MAP can be recovered as a useful substance by the phosphorus crystallization reaction, but on the other hand, there is a problem of high cost due to the addition of chemicals, and the phosphorus recovery rate depends on the concentration of the recovered substance. There was also the problem of becoming unstable.

An object of the present invention is to provide a phosphorus recovery apparatus equipped with a means for recovering high quality magnesium ammonium phosphate MAP as a useful substance from water to be treated such as sewage.

Another object of the present invention is to provide a phosphorus recovery apparatus having means for maintaining a stable and high phosphorus recovery rate at low cost.

[0018]

In order to achieve the above object, the present invention provides, as a first phosphorus recovery apparatus, an anode and a cathode immersed in an electrolytic treatment tank through an anion exchange membrane, and The phosphorus-containing water to be treated is introduced into the compartment between the anion exchange membrane and the cathode, and a means for electrolyzing by energizing between the electrodes is further provided, and the concentrated solution on the anode side has a pH range on the alkaline side. Equipped with a means for causing a phosphorus crystallization reaction in
A phosphorus recovery device is proposed which recovers the phosphorus component in the water to be treated as granular magnesium ammonium phosphate by the phosphorus crystallization reaction.

With this structure, the phosphorus component (PO ₄ ³⁻ ) having a negative charge in the water to be treated by electrolytic treatment
Is attracted to the anode side at the same time as it receives the repulsive force of the cathode. Then, since the phosphorus component permeates the anion exchange membrane that selectively permeates only anions and moves to the anode side, the phosphorus concentration of the concentrated liquid on the anode side becomes high. On the other hand, H
Heavy metals having positive charges such as g and Cd move toward the cathode side without passing through the anion exchange membrane.

Thus, when the water to be treated is subjected to the electrolytic treatment, phosphorus that does not contain heavy metals is recovered in the concentrated liquid on the anode side, and the phosphorus concentration in the concentrated liquid is increased with the recovery. Become. Therefore, if a phosphorus crystallization reaction is performed in the alkaline pH range using this concentrated liquid, the recovered MAP does not contain heavy metals and can be recovered as a useful MAP that can be used as a fertilizer or a fertilizer raw material. In addition, since the concentrated liquid for the crystallization reaction has a high phosphorus concentration in the liquid as described above, it is possible to suppress the decrease in the phosphorus recovery rate due to the low concentration of phosphorus without decreasing the phosphorus recovery rate.

As a result, it is possible to provide a phosphorus recovery device capable of recovering high-quality magnesium ammonium phosphate from the water to be treated with a high recovery rate even if the water to be treated contains heavy metals.

As the second phosphorus recovery apparatus, in the first phosphorus recovery apparatus, the volume of the concentration chamber between the anion exchange membrane and the anode is set between the anion exchange membrane into which the water to be treated is introduced and the cathode. We propose a phosphorus recovery device that is smaller than the volume of the compartment.

During the electrolytic treatment, when the phosphorus component in the water to be treated introduced into the compartment on the cathode side through the anion exchange membrane is moved to the anode side, the volume of the concentration chamber on the anode side is larger than that of the compartment. If it is too large, the concentration of transferred phosphorus will decrease.

However, since the volume of the concentration chamber between the anode and the anion exchange membrane is set to be larger than the volume of the partition between the cathode and the anion exchange membrane, it is possible to suppress the decrease of the phosphorus concentration in the concentration chamber. .

As a third phosphorus recovery device, in the above first phosphorus recovery device, a cation exchange membrane is arranged between the anion exchange membrane and the anode, and the anion exchange membrane and the cation exchange membrane are separated from each other. A phosphorus recovery device is proposed in which water to be treated is introduced and the concentrated liquid on the anode side and the concentrated liquid on the cathode side are mixed to cause a phosphorus crystallization reaction in a pH range on the alkaline side.

According to this structure, it is contained in the water to be treated.
Phosphorus component having negative charge (PO_Four ^3-) Is for electrolytic treatment
Therefore, it is attracted to the anode side and selectively transmits anions.
It permeates the anion exchange membrane to be moved to the anode side. This
As a result, the phosphorus concentration in the concentrated liquid on the anode side becomes high. one
On the other hand, ammoniu having a positive charge as a MAP generating component
Muion (NH_Four ⁺) And magnesium ion (Mg
²⁺) Receives the repulsive force of the cathode and is attracted to the cathode side.
Cation-exchange membrane that allows selective permeation of cations
Permeate through to move to the cathode side for concentration. As a result,
The concentration of the MAP producing component in the concentrated liquid on both sides becomes high.

Since hydrogen ions (H ⁺ ) are generated on the surface of the anode by the electrolytic treatment, the concentrated liquid on the anode side becomes acidic. On the contrary, since hydroxide ions (OH ⁻ ) are generated on the surface of the cathode, the concentrated liquid on the cathode side becomes alkaline.

FIG. 11 shows the pH change characteristic of the water to be treated in the electrolytic treatment according to the present invention. Precipitation water (pH of about 7.5) in the final sedimentation tank of the sewage treatment process was used as the water to be treated, and Pt (titanium substrate) was used as the electrode for batch type electrolytic treatment. The volume on the cathode side was set to 1 through the anion exchange membrane, and the volume ratio on the anode side was set to 0.6. As a result, the pH of the concentrated liquid on the anode side becomes about 2, and the p
H will be about 11.

Therefore, an acidic concentrate containing a high concentration of phosphorus component and an alkaline concentrate containing a high concentration of ammonium and magnesium ions are mixed to form an alkaline p solution.
When the phosphorus crystallization reaction is performed in the H region, the above-mentioned chemical agent such as an alkaline agent for pH adjustment becomes unnecessary, and the phosphorus content in the water to be treated can be recovered as MAP at low cost. And, even if the concentration of the component that becomes the MAP-forming component in the water to be treated is low, the component concentration in each concentrated liquid is maintained high by the electrolytic treatment, so that the addition of a chemical such as magnesium chloride is unnecessary or can be reduced. It is possible to suppress a decrease in the phosphorus recovery rate due to a decrease in the concentration of the MAP producing component in the treated water. As a result,
A phosphorus recovery device that can maintain a stable and high phosphorus recovery rate at low cost can be provided.

As the fourth phosphorus recovery device, in the third phosphorus recovery device, the volume of the concentration chambers on the anode side and the cathode side is set smaller than the volume of the compartment into which the water to be treated is introduced. To propose.

During the electrolytic treatment, the MAP forming component in the water to be treated introduced into the compartment between the anion exchange membrane and the cation exchange membrane moves to the anode side and the cathode side, and then the concentration chambers on the anode side and the cathode side. When the volume is larger than the volume of the compartment, the concentration of the MAP producing component moved to each electrode side becomes diluted and the concentration decreases. In order to deal with this, the volumes of the concentration chambers on the anode side and the cathode side are set to be larger than the volume of the compartment between the anion exchange membrane and the cation exchange membrane. The decrease can be suppressed.

As a fifth phosphorus recovery device, in the third phosphorus recovery device, the mixing ratio of the concentrated liquid on the anode side and the concentrated liquid on the cathode side is detected by detecting the pH in the phosphorus crystallization reaction tank, We propose a phosphorus recovery device that adjusts based on the deviation between the pH value and the set target pH value.

The phosphorus crystallization reaction proceeds in a pH region (pH 8 to pH 9) higher than the stable region of phosphorus existing in an ionic state, and the phosphorus recovery rate depends on the reaction pH as described above. Therefore, when the phosphorus component in the water to be treated is recovered as MAP by the crystallization reaction, maintaining the pH at an appropriate level is an important factor for increasing the phosphorus recovery rate. In particular, when mixing the concentrated solution of the acidic solution and the concentrated solution of the alkaline solution which have been subjected to the electrolytic treatment, the pH is influenced by the mixing ratio, so that the adjustment of this ratio is important.

Therefore, in this structure, when the phosphorus component-containing concentrated liquid which is an acidic liquid and the ammonium and magnesium ion-containing concentrated liquid which is an alkaline liquid are mixed, in order to maintain an appropriate set target pH value, the phosphorus crystal is added. The pH in the precipitation reaction tank was detected, and the mixing ratio of each concentrate was adjusted based on the deviation from the set target pH value.

According to this structure, the pH in the phosphorus crystallization reaction tank can be maintained at the target proper pH without using an alkaline agent for pH adjustment, and fluctuations in pH can be suppressed. As a result, a high phosphorus recovery rate can be stably obtained.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a phosphorus recovery apparatus according to the present invention will be described with reference to FIGS.

[0037]

[First Embodiment] FIG. 1 is a block diagram showing a system configuration and a treatment procedure of a sewage treatment plant when the phosphorus recovery apparatus according to the present invention is applied to the sewage treatment plant. The inflow water RW, which becomes sewage, is first introduced into the activated sludge treatment tank 2 after the fine sand and the suspended solids are settled and separated in the settling tank 1.

The inflow water RW is aerated and mixed with the activated sludge in the activated sludge treatment tank 2 for a predetermined time, and the organic matter is oxidized and decomposed by the action of the activated sludge. Then, the mixed liquid MW of the activated sludge and the treated water in the activated sludge treatment tank 2 is introduced into the final settling tank 3.

In the final settling tank 3, the sludge AS is settled and separated, and the supernatant water is discharged as treated water TW out of the system of the sewage treatment plant. Alternatively, a tertiary treatment is carried out if necessary and the product is discharged to the outside of the system.

On the other hand, the sludge AS that has settled at the bottom of the final settling tank 3 is continuously withdrawn, and part of it is returned to the upstream side of the activated sludge treatment tank 2 as return sludge RA. The sludge increased by decomposing the organic matter is extracted as surplus sludge SA.

The excess sludge SA containing the treated water TW is then separated into a separated liquid and an excess sludge SA by a solid-liquid separation means 4 such as a centrifuge, and the separated liquid is first precipitated as return water BW. It is returned to the upstream side of pond 1.

On the other hand, the excess sludge SA separated by the solid-liquid separation means 4 is then introduced into the anaerobic digestion tank 5.

In the anaerobic digestion tank 5, the organic matter in the excess sludge SA is anaerobically digested (or methane-fermented) by the action of anaerobic bacteria, and if necessary, a digestion gas G containing methane (CH ₄ ) as a main component. Is recovered. Since the digestive gas G contains a trace amount of hydrogen sulfide (H ₂ S) that causes corrosion and air pollution in addition to the useful component methane, the desulfurization means
After passing through (not shown), gas is stored (not shown) and then used as gas.

The digested sludge DS from the anaerobic digestion tank 5 is
It is introduced into the solid-liquid separation means 6 including a centrifuge or the like, where the digested sludge DS is solid-liquid separated into the dehydrated cake S and the digested liquid DL.

In the anaerobic digestion tank 5, phosphorus ingested in the activated sludge in an aerobic state is released. Therefore, the phosphorus concentration in the digestive fluid DL is high.

Next, the digested liquid DL is introduced into the electrolytic treatment tank 7 as the water to be treated W, as shown in FIG. 2, where it is electrolytically separated. As shown in detail in FIG. 3, the electrolytic treatment bath 7 includes a plurality of treatment baths 7 whose interiors are partitioned.
A and 8B are provided, and an anode 8 and a cathode 9 are immersed in the respective tanks 7A and 7B so as to face each other with an anion exchange membrane 10 interposed therebetween. The anion exchange membrane 10 does not allow cations to pass through, but has a function of selectively passing anions.

The anode 8 and the cathode 9 are connected to a stabilized DC power supply 11, and a DC current is passed between both electrodes 8 and 9. As the material of the electrode, in the first embodiment, Pt is formed on the surface.
A coated electrode is selected, but it may be an iron electrode or the like and is not particularly limited.

The digestive liquid DL which becomes the water W to be treated is supplied to the compartment 13 between the anion exchange membrane 10 and the cathode 9 through the protective filter 12. When current is supplied from the stabilized DC power supply 11 between the anode 8 and the cathode 9, Hg and Cd are contained in the water W to be treated.
When a heavy metal having a positive charge is included, the heavy metal having a positive charge is attracted to the cathode 9 side without passing through the anion exchange membrane 10. On the other hand, the phosphorus component of the negative ions in the digestive liquid DL that becomes the water to be treated W is drawn to the anode 9 side and permeates the anion exchange membrane 10 that selectively allows only the anions to move to the anode 8 side. To do. As a result, the concentrated liquid on the side of the anode 8 does not contain heavy metals and has a high phosphorus concentration.

The concentrated liquid AC in the concentrating chamber 14 located on the side of the anode 8 is supplied to the phosphorus crystallization reaction tank 1 which will be described later by the feed pump 15.
6 is supplied. The drainage pump 17 discharges the water W to be treated introduced into the compartment 13 in the electrolytic treatment tank 7 as needed.

Here, the volume Vn of the concentrating chamber 14 between the anode 8 and the anion exchange membrane 10 is the cathode 9 into which the water W to be treated is introduced.
The volume V0 is smaller than the volume V0 of the compartment 13 between the anion exchange membrane 10 and the anion exchange membrane 10, and the decrease in the concentration of phosphorus that has moved to the anode 8 side is suppressed and the degree of concentration of phosphorus is increased.

In the first embodiment, in order to increase the treatment amount, the electrolytic treatment bath 7 is divided into a plurality of treatment baths 7A, 7B, and the electrodes 8, 8 are formed in the divided baths 7A, 7B.
Although 9 and the anion exchange membrane 10 are immersed and arranged, the electrolytic treatment tank 7 may be a single tank. Also, a plurality of single electrolytic treatment tanks 7 may be combined. further,
The inside of the electrolytic treatment tank 7 may be divided into a plurality of sections, and a plurality of these electrolytic treatment tanks 7 may be combined, and the number and internal configuration of the electrolytic treatment tanks 7 are not limited to those of the first embodiment.

Next, the concentrated liquid AC on the anode 8 side, which has been purified and separated and concentrated in the electrolytic treatment tank 7, is stored in the phosphorus crystallization reaction tank 16 arranged downstream of the electrolytic treatment tank 7 as shown in FIG. Is supplied to the crystallization part 18 located at the bottom of the. Further, the crystallization part 18 in the phosphorus crystallization reaction tank 16 has a required amount of magnesium.
(Eg magnesium chloride, magnesium hydroxide) is injected. In the magnesium solution tank 19, magnesium is injected into the phosphorus crystallization reaction tank 7 via the chemical injection pump 20. Furthermore, an alkaline agent (for example, sodium hydroxide) is injected into the crystallization part 18 in the phosphorus crystallization reaction tank 16 as needed. In the alkaline agent solution tank 21, the alkaline agent is injected into the phosphorus crystallization reaction tank 16 via the chemical solution injection pump 22.

The pH in the phosphorus crystallization reaction tank 16 is measured by a pH meter 2
The detected value pH 0 of the pH meter 23 is input to the calculator 24. On the other hand, the set target value pHs on the alkaline side is previously input to the calculator 24. Then, the flow rate of the chemical liquid injection pump 22 that injects the alkaline agent is controlled based on the deviation ΔpH between the set target value pHs and the detected value pH0, and is controlled so as to maintain the set target value pHs.

In the reaction tank 16, the pH of the supplied liquid is maintained at an appropriate predetermined pH of the set target value pHs, so that in the phosphorus crystallization reaction tank 16, the phosphorus crystallization reaction represented by the formula (1) is performed. Progresses and MAP is deposited. In the phosphorus crystallization reaction tank 16, seed crystals (not shown, for example, MAP,
Alternatively, phosphate rock powder) is supplied, and the precipitation reaction proceeds selectively on the seed crystal surface to form fine MAP. Then, seed crystals are supplied as needed.

Air is supplied to the lower part of the phosphorus crystallization reaction tank 16 from a blower 25 through an air diffuser 26 having a large number of holes, and the liquid in the tank 16 is agitated and mixed. Fine MAP
The particle growth progresses in the granulation reaction section 27 while being stirred and mixed, and at the same time, the granulation reaction section 27 rises to rise to the precipitation section 28.
Flow into. Here, MAP is sedimented and separated, and the sedimentation part 2
The dephosphorized water PW from which the MAP has been settled and separated while being returned to the granulation reaction section 27 from 8 overflows in the settling section 28 and is first returned to the upstream side of the settling tank 1. The circulation pump 29 is used for the crystallization unit 18 from the precipitation unit 28 by the pump.
The MAP containing liquid is returned to.

On the other hand, the MAP having a large grain size grown with the progress of the crystallization reaction settles and accumulates at the bottom of the phosphorus crystallization reaction tank 16. The accumulated growth MAP is taken out from the extraction tube 30 provided at the bottom of the phosphorus crystallization reaction tank 16 as needed.
Is discharged from the system through the on-off valve 31. The MAP discharged together with the liquid is separated and collected by the solid-liquid separation means 32. The separated liquid SW is returned to the precipitation part 28 of the phosphorus crystallization reaction tank 16 by the recovery liquid pump 33.

[0057]

Second Embodiment Next, a second embodiment of the phosphorus recovery apparatus according to the present invention will be described with reference to FIGS.

In FIG. 4, the digested liquid D which becomes the water W to be treated.
L is introduced into the electrolytic treatment tank 7, and here, phosphorus having a negative charge that becomes a MAP-forming component contained in the digestive juice DL.
It is electrolytically separated into a (PO ₄ ³⁻ ) component and a positively charged ammonium ion (NH ₄ ⁺ ) and magnesium ion (Mg ²⁺ ).

In FIG. 5, electrolytic treatment tanks 7C and 7D are used.
Inside, an anode 8 and a cathode 9 are arranged so as to face each other.
An anion exchange membrane 10 and a cation exchange membrane 40 are immersed and arranged between the anode 8 and the cathode 9. And
Among the respective membranes 10 and 40, the anion exchange membrane 10 is
It is located on the side of the anode 8. On the other hand, the cation exchange membrane 40 is arranged at the cathode 9. The anion exchange membrane 10 does not allow cations to pass therethrough as described above, but allows anions to pass therethrough. On the contrary, the cation exchange membrane 40 does not allow anions to pass through, but allows cations to pass through.

The digestive liquid DL which becomes the water W to be treated is supplied to the compartment 41 between the anion exchange membrane 10 and the cation exchange membrane 40 via the protective filter 12. When the both electrodes 8 and 9 are energized, the negative ion phosphorus component in the digestive fluid DL permeates the anion exchange membrane 10 and moves to the anode 8 side to be concentrated. On the other hand, positive ions such as ammonium ions and magnesium ions in the digestive fluid DL pass through the cation exchange membrane 40, move to the cathode 9 side, and are concentrated. Here, the volume Vn of the concentrating chambers 14A and 14B between the electrodes 8 and 9 and the ion exchange membranes 10 and 40 is smaller than the volume V0 of the compartment 41 into which the water W to be treated is introduced, and each MAP producing component. It is set to increase the degree of concentration.

As shown in FIG. 4, the concentrated liquid KC on the cathode 9 side and the concentrated liquid AC on the anode 8 side, which have been separated and concentrated in the electrolytic treatment tank 7, are phosphorus crystallizations arranged on the downstream side of the electrolytic treatment tank 7. It is supplied to the crystallization part 18 located at the bottom of the reaction tank 16.

Here, the pH of the concentrated liquid KC on the cathode 9 side is
By the electrolytic treatment in the electrolytic treatment tank 7, hydroxide ions (OH −) are generated on the surface of the cathode 9, and thus the alkaline nature is exhibited. on the other hand,
The pH of the concentrated liquid AC on the anode 8 side is acidic because hydrogen ions (H +) are generated on the surface of the anode 8. Therefore, when the concentrated solutions KC and AC are mixed and the phosphorus crystallization reaction is performed at an appropriate pH, the adjustment of the mixing ratio of the concentrated solutions is controlled based on the pH detection result in the phosphorus crystallization reaction tank 16.

As shown in detail in FIG. 6, the pH meter 23
The pH in the phosphorus crystallization reaction tank 16 is detected at, and the detection value pH0 of the pH meter 23 is input to the calculator 24. on the other hand,
This calculator 24 has a set target value pHs on the alkaline side.
Is previously input. Then, based on the deviation ΔpH between the set target value pHs and the detected value pH0, the feed pump 15 for introducing the concentrated solutions KC and AC into the phosphorus crystallization reaction tank 16, or
The flow rate of the liquid supply pump 54 is controlled, and the mixing ratio of the concentrated liquids KC and AC is adjusted so as to maintain the set target value pHs.

[0064]

[Third Embodiment] In the second embodiment, the single electrolytic treatment tank 7 is used. However, as in the third embodiment shown in Fig. 7, a plurality of electrolytic treatment tanks 50A and 50B are alternately provided with the water W to be treated. The digestive fluid DL to be obtained may be electrolyzed and separated.

A switching valve 51A on the inlet side of one of the electrolytic treatment tanks 50A and 50B.
Is opened and the digestive liquid DL to be treated water W is introduced into the electrolytic treatment tank 50A. Then, in this electrolytic treatment tank 50A, electrolytic processing is performed, and the switching valve 52A on the anode 8 side and the switching valve 53 on the cathode 9 side located on the outlet side of the electrolytic treatment tank 50A.
When A is opened, the concentrated liquid AC on the anode 8 side and the concentrated liquid KC on the cathode 9 side are supplied to the phosphorus crystallization reaction tank 16 via the respective supply pumps 15 and 54.

On the other hand, after supplying the concentrates AC and KC,
The switching valves 52A and 53A located on the outlet side of the electrolytic treatment tank 50A are closed. At the same time, the switching valve 55 located on the inlet side of the electrolytic treatment tank 50A is opened, and the supply pump 56
Concentrated liquid NC such as tap water according to each ion exchange membrane 1
The concentrated liquid chambers 14A and 14B between the electrodes 0 and 40 and the electrodes 8 and 9 are supplied. Further, the digestive liquid in the compartment 41 after the electrolytic treatment is discharged by the drainage pump 58 by opening the switching valve 57A. Then, after the discharge is completed, the switching valve 57A is closed while the switching valve 51A is opened, and new digestive liquid DL is supplied to the compartment 41 for electrolytic treatment.

Contrary to the above, while the electrolytic treatment is proceeding in the electrolytic treatment tank 50A, the concentrated liquids AC and K from the electrolytic treatment tank 50B are discharged.
C is supplied to the phosphorus crystallization reaction tank 16 and a plurality of electrolytic treatment tanks 50A and 50B are alternately operated, whereby the concentrated solutions AC and KC electrolytically treated are continuously supplied to the phosphorus crystallization reaction tank 16. Will be supplied.

That is, while one electrolytic treatment tank 50A is in progress of electrolytic treatment, the switching valve 52B on the anode 8 side and the switching valve 53 on the cathode 9 side located at the outlet side of the other electrolytic treatment tank 50B.
B is opened, and the concentrated liquid AC on the anode 8 side and the concentrated liquid KC on the cathode 9 side are supplied into the phosphorus crystallization reaction tank 16 via the respective supply pumps 15 and 54. On the other hand, each concentrate AC, KC
After the supply of, the switching valves 52B and 53B located on the outlet side of the electrolytic treatment tank 50B are closed and the electrolytic treatment tank 50B is closed.
The switching valve 55B located on the inlet side of the liquid is opened, and the liquid NC to be concentrated is supplied to the concentrated liquid chambers 14A, 1 between the ion exchange membranes and the electrodes.
Supply to 4B. At the same time, the digested liquid after the electrolytic treatment in the compartment 41 is discharged by opening the switching valve 57B. Then, after the discharge is completed, the switching valve 57B is closed.

On the other hand, the switching valve 51B is opened to supply a new digestive liquid DL to the compartment 41 for electrolytic treatment, and then the concentrated liquids AC and KC are supplied from the other electrolytic treatment tank 50A. The above-mentioned opening / closing operation of each switching valve and the instruction thereof and the operation instruction of each pump are performed based on a sequence previously input to a controller (not shown).

In the third embodiment, the electrolytic treatment bath 7 is partitioned into a plurality of compartments, and the electrodes 8 and 9 and the ion exchange membrane 1 are placed in the respective partitioned treatment baths 50A and 50B.
Although 0 and 40 are immersed and arranged, the electrolytic treatment tank 7 may be an independent single tank. In addition, a single electrolytic treatment tank 7
You may combine two or more. Furthermore, the inside of the electrolytic treatment tank 7 may be divided into a plurality of sections, and a plurality of these electrolytic treatment tanks 7 may be combined. The configuration of the electrolytic treatment tank 7 is the same as that of the third embodiment.
Not limited to only.

In the third embodiment, the flow rate of one of the liquid supply pumps 54 is constant and the flow rate of the other liquid supply pump 15 is controlled to adjust the mixing ratio of the concentrated liquids KC and AC. However, the flow rate of both liquid supply pumps 15 and 54 may be controlled to adjust the mixing ratio, and the present invention is not limited to the third embodiment.

In the case where it is constructed as described above, in this phosphorus recovery apparatus, the phosphorus component in the water to be treated is recovered to the anode side by electrolytic treatment through the anion exchange membrane,
The concentrated solution on the anode side is used to cause a phosphorus crystallization reaction in the alkaline pH range. As a result, even if the water to be treated contains a heavy metal, the heavy metal remains on the cathode side, and the concentrated liquid containing the phosphorus component on the anode side does not contain the heavy metal. For this reason, if the phosphorus crystallization reaction is performed in the alkaline pH range using this concentrated solution on the anode side, the recovered MAP
It contains no heavy metals and can be recovered as useful MAP that can be used as fertilizer or fertilizer raw material. Further, since the concentrated liquid for the crystallization reaction has a high phosphorus concentration in the liquid, the phosphorus recovery rate does not decrease. As a result,
It is possible to provide a phosphorus recovery device that can recover high-quality MAP with a high recovery rate from phosphorus-containing treated water such as sewage.

In the phosphorus recovery system of the third embodiment,
By the electrolytic treatment through the anion and cation exchange membrane, the phosphorus component is concentrated to the acidic water side, while the ammonium ion and the magnesium ion are concentrated to the alkaline water side, and both are mixed in the alkaline pH range. The crystallization reaction is in progress. Thereby, when the phosphorus crystallization reaction is performed, the concentrated liquid AC of the acidic liquid and the concentrated liquid KC of the alkaline liquid are used.
Since and are used as a mixture, the alkaline agent necessary for maintaining the alkaline side at an appropriate pH is unnecessary.

Further, even if the concentration of the component as the MAP raw material in the water to be treated W is low, the component concentration in each concentrated liquid is maintained high by the electrolytic treatment through the anion and cation exchange membranes. This makes it possible to eliminate or reduce the addition of a chemical such as magnesium chloride that supplements the deficiency, and suppress the decrease in phosphorus recovery rate due to the decrease in the raw material component concentration. As a result, according to the third embodiment, it is possible to provide a phosphorus recovery apparatus that can obtain a stable and high phosphorus recovery rate at low cost.

Further, in the third embodiment, when mixing the phosphorus component-containing concentrated liquid which is an acidic liquid and the ammonium and magnesium ion-containing concentrated liquid which is an alkaline liquid, the mixing ratio of each concentrated liquid is set in the phosphorus crystallization reaction tank. The adjustment is made based on the deviation between the pH detection result and the set target pH value. In this way, by adjusting the mixing ratio of each concentrated solution, the pH in the phosphorus crystallization reaction tank can be maintained at a target proper pH without using an alkaline agent for pH adjustment, and the fluctuation of pH can be prevented. Can be suppressed. As a result, p
A high phosphorus recovery rate can be stably obtained without decreasing the phosphorus recovery rate as H is lowered.

[0076]

According to the present invention, there is provided a phosphorus recovery apparatus capable of recovering high-quality magnesium ammonium phosphate containing no heavy metal by using the electrolytically treated concentrated solution on the anode side for the phosphorus crystallization reaction. .

In addition, since an alkali agent necessary for adjusting the pH during the phosphorus crystallization reaction is not necessary and the pH fluctuation during the crystallization reaction can be suppressed, the recovery rate of phosphorus-containing treated water such as sewage at a low cost and a high recovery rate. It is possible to provide a phosphorus recovery device that can obtain

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration of an entire system of Embodiment 1 of a phosphorus recovery apparatus according to the present invention.

FIG. 2 is a phosphorus crystallization reaction tank 1 of the phosphorus recovery apparatus of the first embodiment.
It is a figure which shows the detailed structure of 6 circumference | surroundings.

FIG. 3 is a diagram showing a detailed configuration around an electrolytic treatment tank 7 of the phosphorus recovery apparatus of the first embodiment.

FIG. 4 is a diagram showing a detailed configuration around a phosphorus crystallization reaction tank 16 of a second embodiment of a phosphorus recovery apparatus according to the present invention.

FIG. 5 is a diagram showing a detailed configuration around an electrolytic treatment tank 7 of a phosphorus recovery apparatus according to a second embodiment.

FIG. 6 is a diagram showing a more detailed structure around the phosphorus crystallization reaction tank 16 of the second embodiment.

FIG. 7 is a diagram showing a detailed configuration around a phosphorus crystallization reaction tank 16 of a third embodiment of a phosphorus recovery apparatus according to the present invention.

FIG. 8 is a characteristic diagram showing a relationship between a magnesium addition rate and a phosphorus recovery rate.

FIG. 9 is a characteristic diagram showing the relationship between pH and phosphorus recovery rate.

FIG. 10 is a characteristic diagram showing a relationship between ammonium ion concentration and phosphorus recovery rate.

FIG. 11 is a characteristic diagram showing pH changes on the cathode side and the anode side before and after electrolytic treatment according to an embodiment of the present invention.

[Explanation of symbols]

1 first settling tank 2 Activated sludge treatment tank 3 final settling tank 4 Solid-liquid separation means 5 Anaerobic digester 6 Solid-liquid separation means 7 Electrolytic treatment tank 8 anode 9 cathode 10 Anion exchange membrane 11 DC stabilized power supply 12 Protection filter 13 compartments 14 Concentration room 15 Supply pump 16 Phosphorus crystallization reaction tank 17 Drainage pump 18 crystallization part 19 Magnesium solution tank 20 Chemical injection pump 21 Alkaline solution tank 22 Chemical injection pump 23 pH meter 24 arithmetic unit 25 Blower 26 Air diffuser 27 Granulation reaction part 28 sedimentation part 29 Circulation pump 30 Extraction tube 31 on-off valve 32 solid-liquid separation means 33 Recovery liquid pump 40 cation exchange membrane 41 compartment 50 Electrolytic treatment tank 51 switching valve 52 Switching valve 53 Switching valve 54 Liquid supply pump 55 Switching valve 56 supply pump 57 Switching valve 58 drainage pump AC concentrate AS sludge BW return water DL digestive fluid DS digested sludge G digestion gas KC concentrate MAP Magnesium ammonium phosphate MW mixed liquid NC Concentrated liquid PW dephosphorized water RA return sludge SA surplus sludge TW treated water W treated water

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 9/02 625 B01D 9/02 625Z 61/44 500 61/44 500 61/46 61/46 C02F 1/46 C02F 1 / 46 Z (72) Inventor Enrobu Ichiro 72-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Electric Power and Electrical Development Laboratory (72) Inventor Shoji Watanabe 7-2 Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Incorporated Hitachi, Ltd. Electric Power & Electric Development Laboratory (72) Inventor Toshikatsu Mori 7-21 Omika-cho, Hitachi City, Ibaraki Prefecture F-Term (Informative) 4D006 in Hitachi Electric Power & Electric Development Laboratory GA13 KA31 KB01 MA13 MA14 MB07 PB08 PB27 4D038 AA08 AB48 AB54 BA04 BA06 BB10 4D061 DA08 DB19 DC25 DC26 EA02 EB01 EB13 EB17 EB19 EB20

Claims (5)

[Claims] 1. An anode and a cathode are immersed in an electrolytic treatment tank via an anion exchange membrane, and phosphorus-containing water to be treated is introduced into a compartment between the anion exchange membrane and the cathode,
A means for conducting an electrolytic treatment by energizing between both electrodes is further provided, and a means for causing a phosphorus crystallization reaction in the concentrated liquid on the anode side in a pH range on the alkaline side, and a phosphorus component in water to be treated by the phosphorus crystallization reaction. Is recovered as granular magnesium ammonium phosphate. 2. The phosphorus recovery apparatus according to claim 1, wherein the volume of the concentration chamber between the anion exchange membrane and the anode is the volume of the compartment between the anion exchange membrane into which the water to be treated is introduced and the cathode. A phosphorus recovery device characterized by being set smaller than the above. 3. The phosphorus recovery apparatus according to claim 1, wherein a cation exchange membrane is arranged between the anion exchange membrane and the cathode,
The water to be treated is introduced into the compartment between the anion exchange membrane and the cation exchange membrane, and the concentrated solution on the anode side and the concentrated solution on the cathode side are mixed to perform a phosphorus crystallization reaction in the pH range on the alkaline side. A phosphorus recovery device characterized by: 4. The phosphorus recovery apparatus according to claim 3, wherein the volumes of the concentration chambers on the anode side and the cathode side are set smaller than the volume of the compartment into which the water to be treated is introduced. apparatus. 5. The phosphorus recovery apparatus according to claim 3, wherein the pH in the phosphorus crystallization reaction tank to which each concentrated solution is supplied from the electrolytic treatment tank side is detected, and the pH value and the alkaline-side setting target are set. A phosphorus recovery device, wherein the mixing ratio of the concentrated liquid on the anode side and the concentrated liquid on the cathode side is adjusted based on the deviation from the pH value.