JP2007105707A - Method of removing phosphorus in water by crystallization, and device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of removing phosphorus in water by crystallization capable of performing pH adjustment and neutral treatment without using chemicals and capable of solving a problem such as clogging of a diaphragm in electrolytic treatment, and to provide a device for performing the method of removing phosphorus in water by crystallization. <P>SOLUTION: The device for performing the method of removing phosphorus in water by crystallization comprises a crystallization dephosphorization tank 10 and an electrolyzer 8 for electrolytically treating clear water such as tap water, and is provided with such a composition that strong alkaline water 9 produced in the electrolyzer 8 is introduced into the inlet side of water to be treated of the crystallization dephosphorization tank 10 and strong acidic water 11 produced in the electrolyzer 8 is introduced into the outlet side of water to be treated of the crystallization dephosphorization tank 10, whereby the water to be treated is pH-adjusted and is subjected to phosphorus crystallization reaction in an alkaline pH region and, thereafter, treated water is neutralized by the strong acidic water obtained by electrolytic treatment together with the strong alkaline water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for crystallizing, removing, and recovering phosphorus contained in water to be treated as a phosphorus compound, and in particular, phosphorus crystals that precipitate and remove phosphorus in water to be treated under a high pH state. The present invention relates to an analysis and removal method and apparatus.

  As a method for precipitating and removing phosphorus in water as a phosphorus compound (crystallization dephosphorization method), a MAP method for producing magnesium ammonium phosphate and a HAP method for producing hydroxyapatite have been put into practical use.

  The reaction of the MAP (magnesium ammonium phosphate) method produces magnesium ammonium phosphate from magnesium, ammonium, phosphorus and hydroxyl groups in the liquid as described below.

_{^{Mg 2+ + NH 4 + + HPO}} 4 2+ OH - + 6H 2 O → MgNH 4 PO 4 · 6H 2 O (MAP) + H 2 O
The amount of MAP deposited increases as the pH increases, and the phosphorus concentration in the treated water decreases. However, from the balance with the chemical amount required for neutralization after the treatment, the treatment is generally carried out in the range of pH 8-10.

  On the other hand, the HAP method is a method in which phosphorus in water reacts with calcium to produce HAP (hydroxyapatite). HAP is a kind of calcium phosphate and is produced as follows.

_{^{5Ca 2+ + 3PO 4 3- + OH}} - → Ca 5 (PO 4) 3 (OH)
Also in the case of the HAP method, as the pH is higher, the amount of HAP precipitated increases and the phosphorus concentration in the treated water tends to decrease. However, as in the MAP method, the treatment is generally carried out in the pH range of 8-10.

  Sewage treatment is generally performed by biological reaction. Microbial treatment is an excellent treatment method that can obtain clean wastewater because it removes organic substances expressed as BOD and also takes in and treats phosphorous and nitrogen in water into the body of the microorganism. In this microorganism treatment method, it is necessary to remove the grown microorganisms in a timely manner. The removed microorganisms are incinerated after reducing the water as much as possible with a dehydrator. On the other hand, the separated liquid (desorbed liquid) discharged from the dehydrator is returned to the aforementioned biological reaction tank, and the microbial treatment is performed again. Here, in the detachment liquid, a part of the above-mentioned phosphorus taken up by the microorganism is released, so that the phosphorus concentration is high, and when this is returned to the biological reaction tank, the amount that can be processed by the biological reaction. As a result of the accumulation of the above phosphorus, there has been a problem that the phosphorus concentration in the treated effluent of microorganisms increases.

  Therefore, in the case of the above-mentioned biological treatment, there is a problem that phosphorus cannot be completely treated. Therefore, in such a processing system, it is expected to apply the HAP method or the MAP method that can fix and remove phosphorus, and development is being promoted. In both the HAP method and the MAP method, as described above, the reaction proceeds faster as the pH is higher. However, when the pH is increased, the required amount of chemicals (alkali) to be added to increase the pH increases, resulting in an increase in running cost. Furthermore, since there is a concern that treated water having a high pH may affect the subsequent treatment, neutralization treatment is necessary. An increase in the cost of chemicals (acids) required for this is also a problem.

  By the way, as described above, there has also been proposed a method in which the water to be treated is directly subjected to electrolytic treatment without adding a chemical to change the pH of the water to be treated for crystallization (see, for example, Patent Documents 1 and 2).

  Patent Document 1 proposes “providing a phosphorus recovery device provided with a means for recovering high-quality ammonium magnesium phosphate MAP as a useful product from treated water such as sewage”. Means for immersing the anode and the cathode through the anion exchange membrane, introducing the phosphorus component-containing water into the compartment between the anion exchange membrane and the cathode, and conducting the electrolytic treatment by energizing between the electrodes. And a means for causing a phosphorus crystallization reaction of the concentrated solution on the anode side in an alkaline pH range, and recovering the phosphorus component in the water to be treated as particulates of magnesium ammonium phosphate by the phosphorus crystallization reaction. A phosphorus recovery apparatus characterized by the above.

  Further, Patent Document 2 proposes “providing a method for removing and / or recovering phosphorus with high efficiency, which is extremely simple in processing operation, does not add chemicals, and has high efficiency”. Immerse the electrode in the bath, apply a DC voltage to the electrode to generate hydroxide ions by migration and / or electrolysis of cations in the treated water, and phosphate ions in the treated water Is disclosed as a method for removing phosphorus, characterized in that it is precipitated as a sparingly soluble salt in water.

Further, according to claims 3, [0005] and [0007] of Patent Document 2, “the electrode is a multiple electrode” and “a water permeable diaphragm is provided between the anode and the cathode, respectively. As the water-permeable diaphragm, a sponge or the like can be exemplified. ”“ The multiple electrode used in the present invention preferably has a hole through which ions and water to be treated can pass. The multiple electrode is preferably porous or mesh, and more specific electrode shapes include a wire mesh, an expanded mesh, etc. When a plurality of cathodes are used with respect to the anode, the periphery of the cathode becomes an alkaline region. , Phosphate ions are easily crystallized and precipitated as apatite, Ca salt, and Mg salt.
JP 2003-39081 A JP 2002-361258 A

  By the way, when the water to be treated is directly subjected to electrolytic treatment as in the inventions of Patent Documents 1 and 2, depending on components such as turbidity, oil, organic lysate, phosphorus compound and microorganisms contained in the water to be treated. There is a problem that the partition or the diaphragm provided between the electrodes is blocked and cannot be operated.

  In the case of Patent Document 1, the ion exchange membrane as a diaphragm is blocked, and in the case of Patent Document 2, in addition to the diaphragm between the anode and the cathode being blocked, a porous or meshed multi-electrode is formed. Occlusion is also considered a problem.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to perform pH adjustment and neutralization treatment without using chemicals, and in electrolytic treatment. An object of the present invention is to provide a method and apparatus for removing phosphorus crystallization in water that can solve problems such as blockage of the diaphragm.

  The above-mentioned subject is achieved by the following. That is, in the water crystallization removal method for removing phosphorus in the water to be treated by adjusting the pH of the water to be treated and causing a phosphorus crystallization reaction under an alkaline pH range, the pH adjustment of the water to be treated is performed as described above. It is performed using electrolyzed water obtained by electrolyzing water different from the water to be treated (Claim 1).

  Further, in the method for removing phosphorus crystallization in water according to claim 1, the water different from the water to be treated is clarified water such as tap water or ground water, and electrolyzed water for adjusting the pH to be alkaline is strong. Alkaline water is used (claim 2).

  Further, in the method for removing phosphorus crystallization in water according to claim 1 or 2, the treated water after adjusting the pH of the water to be treated and causing the phosphorus crystallization reaction in an alkaline pH range is used together with the strong alkaline water. Neutralization treatment is performed with strongly acidic water obtained by electrolytic treatment (claim 3).

  In addition, as the invention of the phosphorus crystallization removing apparatus, the inventions of the following claims 4 to 5 are preferable. That is, an apparatus for carrying out the phosphorus crystallization removal method according to claim 3, wherein a crystallization dephosphorization tank that adjusts pH of water to be treated and causes a phosphorus crystallization reaction in an alkaline pH range, An electrolytic bath for electrolytically treating water, introducing strong alkaline water generated in the electrolytic bath to the treated water inlet side of the crystallization dephosphorization bath, and the treated water outlet side of the crystallization dephosphorizing bath (6), a structure for introducing strongly acidic water generated in the electrolytic cell is provided.

  Further, the present invention relates to the microbial treatment of sewage, and in the apparatus for removing phosphorus crystallization in water according to claim 4, the water to be treated is a waste sludge detachment liquid after biologically treating the waste water (claim 5). ).

  According to the present invention, strong alkaline water obtained by electrolytic treatment of clear water such as tap water is used as a pH adjusting solution for the HAP method or MAP method, and strong acid water as a by-product is used as a medium. The system was used as a hydrating agent. As a result, it is possible to perform pH adjustment and neutralization without using chemicals required for pH adjustment, and it is possible to save labor such as running costs and chemical replenishment due to chemical costs. Furthermore, since clear water such as tap water is subjected to electrolytic treatment, problems such as blockage of the diaphragm in the electrolytic tank can be solved unlike the electrolytic treatment of water to be treated containing turbid components as in the conventional method.

  According to the present invention, there is provided a method and apparatus for removing phosphorus crystallization in water that can perform pH adjustment and neutralization without using chemicals, and that can solve problems such as blockage of the diaphragm in electrolytic treatment. it can.

  Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic system configuration diagram of a phosphorus crystallization removal apparatus showing an embodiment of the present invention. As the water to be treated, the system configuration in the case of using a waste sludge effluent after biological treatment of wastewater. FIG.

  In FIG. 1, 1 is drainage, 2 is a biological reaction tank, 3 is a sedimentation separation tank, 4 is treated water, 5 is a dehydrator, 6 is waste sludge, 7 is a desorption liquid, 8 is an electrolytic cell, and 9 is a strong alkali. Water, 10 is a crystallization dephosphorization tank, 11 is strongly acidic water, 12 is sodium chloride, 13 is tap water, 14 is a partition, 15 is a positive electrode, and 16 is a negative electrode. The operation of the apparatus shown in FIG. 1 is as follows.

  Wastewater 1 such as sewage is biologically treated in a biological reaction tank 2. This biologically treated treated water is subjected to solid-liquid separation in the sedimentation tank 3. The liquid is discharged out of the system as treated water 4. On the other hand, the solid separated by sedimentation is discharged from the lower part of the sedimentation separation tank and separated into waste sludge 6 and desorbed liquid 7 dehydrated by the dehydrator 5. Here, the waste sludge 6 is discharged and treated outside the system. On the other hand, after the desorbing liquid 7 is mixed with strong alkaline water 9 generated in the electrolytic cell 8, phosphorus in the liquid is removed in the crystallization dephosphorizing tank 10 by the HAP method or the MAP method. After the phosphorus in this liquid is removed and the treated water exits the crystallization dephosphorization tank 10, it is mixed with the strongly acidic water 11 produced in the electrolytic cell 8, and then the waste water inlet side of the biological reaction tank 2. To reflux.

  As an electrolyzed water source for the electrolyzer 8, tap water 13 to which sodium chloride 12 is added is supplied from the outside. In the electrolytic cell, positive and negative electrodes 15 and 16 are provided via partition walls 14. By applying an appropriate voltage to this, a difference in ion concentration occurs between water tanks separated by a partition wall, and strong alkaline water (for example, pH 11.0 to 12.2) and strongly acidic water (for example, pH 2.0 to 3.5) Is generated.

The typical system block diagram of the phosphorus crystallization removal apparatus which shows the Example of this invention.

Explanation of symbols

1: drainage, 2: biological reaction tank, 3: sedimentation separation tank, 4: treated water, 5: dehydrator, 6: waste sludge, 7: desorbed liquid, 8: electrolysis tank, 9: strong alkaline water, 10: Crystallization dephosphorization tank, 11: strongly acidic water, 12: sodium chloride, 13: tap water, 14: partition, 15: positive electrode, 16: negative electrode.

Claims (5)

  In the water crystallization removal method for removing phosphorus in the water to be treated by adjusting the pH of the water to be treated and causing a phosphorus crystallization reaction in an alkaline pH range, the pH adjustment of the water to be treated is performed in the water to be treated. A method for removing phosphorus crystallization in water, which is performed using electrolyzed water obtained by electrolyzing water different from water.   In the method for removing phosphorus crystallization in water according to claim 1, the water different from the water to be treated is clarified water such as tap water or ground water, and the electrolyzed water for adjusting the pH to be alkaline is strongly alkaline water. A method for removing phosphorus crystallization in water.   3. The method for removing phosphorus crystallization in water according to claim 1, wherein the water to be treated is subjected to pH adjustment and subjected to phosphorus crystallization reaction in an alkaline pH range by electrolytic treatment together with the strong alkaline water. A method for removing phosphorus crystallization in water, comprising neutralizing with the strong acid water obtained.   An apparatus for carrying out the phosphorus crystallization removal method according to claim 3, wherein the crystallization dephosphorization tank for adjusting the pH of the water to be treated and performing a phosphorus crystallization reaction in an alkaline pH range, and electrolyzing the clarified water A strong alkaline water generated in the electrolytic tank is introduced into the treated water inlet side of the crystallization dephosphorization tank, and the electrolytic solution is introduced into the treated water outlet side of the crystallization dephosphorization tank. An apparatus for removing phosphorus crystallization in water, comprising a configuration for introducing strongly acidic water generated in a tank.   The underwater phosphorus crystallization removal apparatus according to claim 4, wherein the water to be treated is a waste sludge detachment liquid after biological treatment of waste water.

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