JP2007117874A - Method and apparatus for treating wastewater containing component to be crystallized - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for treating wastewater which enables crystallization treatment without addition of an agent for crystallization, and enables a stable operation at a high concentration rate without external addition of a calcium softening agent in subsequent distillation concentration since the concentration of components to be crystallized in the wastewater is reduced by the crystallization treatment. <P>SOLUTION: Wastewater containing the components to be crystallized is subjected to treatment combining the distillation concentration treatment and crystallization treatment. A part of concentrated wastewater obtained by the distillation concentration is taken outside of a system, and the remainder is introduced to a crystallization process, and crystallized to take out crystallized material. In the combined treatment, the concentration of the components to be crystallized in the wastewater flowing into a distillation concentration apparatus is reduced by the crystallization treatment, which enables the high concentration rate of the distillation concentration. Distillation concentrate with a high concentration of the components to be crystallized is substituted for the addition of the agent for crystallization, required for the crystallization treatment, which enables the crystallization treatment without the addition of the agent for crystallization. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to the treatment of wastewater containing components to be crystallized, such as sewage, human waste, septic tank sludge, general waste disposal site leachate or other industrial wastewater, or wastewater that has been subjected to biological treatment or the like. The present invention relates to a method and an apparatus for subjecting a waste water containing calcium and phosphate ions, or fluorine ions and sulfate ions to distillation concentration treatment and crystallization treatment.

  Conventionally, in a method of separating wastewater containing components to be crystallized such as wastewater containing calcium and phosphate ions, or fluorine ions and sulfate ions into condensed water and concentrated wastewater by distillation, the distilled water alone is clarified by distillation alone. However, the concentration of the crystallization target component of the concentrated wastewater becomes high due to the concentration of the wastewater, and the scale is deposited by the crystallization and adheres to the evaporation surface in the distillation apparatus. There wasn't. As a result, there has been a problem that the amount of concentrated wastewater that becomes waste cannot be reduced.

  Therefore, the object of the present invention is to reduce the concentration of the crystallization target component of the wastewater flowing into the distillation concentration apparatus by combining the distillation concentration process and the crystallization process, and to increase the crystallization target component by the distillation concentration process. It is another object of the present invention to provide a wastewater treatment method and a treatment apparatus for enabling crystallization treatment.

The present invention has solved the problems by the following means.
(1) Vapor produced by distillation by introducing a mixture of waste water containing the crystallization target component with concentrated waste water having a reduced concentration of the crystallization target component from the subsequent crystallization step into the distillation concentration step. Is taken out as condensed water, and part of the concentrated wastewater obtained by distillation and concentration is taken out of the system, the rest is introduced into the crystallization process to crystallize, the crystallized product is taken out, and the crystallization from the crystallization process A method for treating wastewater containing a crystallization target component, wherein the concentrated wastewater having a reduced concentration of the target component is circulated in order to mix with the wastewater containing the crystallization target component.
(2) The pH of the liquid in the distillation concentration step is adjusted to 4 to 7 by adjusting the pH of the mixed water of the waste water containing the crystallization target component and the concentrated waste water in which the concentration of the crystallization target component is reduced. The method for treating wastewater containing a crystallization target component according to (1), wherein the pH of the liquid in the crystallization step is adjusted to 6 to 9 by adjusting the remaining pH of the concentrated wastewater entering the crystallization step .

(3) The method for treating wastewater containing a crystallization target component according to (1) or (2), wherein a crystallization chemical is added to the concentrated wastewater entering the crystallization step.
(4) In the crystallization step, the water level of the crystallization apparatus is maintained constant, and the amount of crystallized matter stored in the crystallization apparatus is managed by a load cell. The processing method of the waste_water | drain containing the crystallization object component of any one.
(5) The crystallized product is at least one of calcium phosphate, calcium hydrogen phosphate, phosphate phosphate, calcium fluoride, and calcium sulfate, wherein any one of the above (1) to (4) is described. A method for treating wastewater containing the components to be crystallized.

(6) Introducing mixed water obtained by mixing waste water containing the crystallization target component with concentrated effluent from a subsequent crystallization apparatus with reduced concentration of the crystallization target component, concentrating by distillation, and condensing water generated by distillation As a distillation concentrating device to be taken out, a part of the concentrated drainage from the distillation concentrating device is discharged from a pipe for discharging out of the system, and the rest is introduced into the crystallizer from the pipe to be crystallized, and a crystallized substance takeout pipe And a pipe for circulating the concentrated waste water in which the concentration of the crystallization target component of the crystallization device is reduced to the introduction pipe of the waste water containing the crystallization target component. Wastewater treatment equipment containing ingredients.
(7) The apparatus for treating wastewater containing a crystallization target component as described in (6) above, wherein the distillation concentration apparatus has a thermoplastic synthetic resin thin film as an evaporation surface.
(8) The waste water containing the crystallization target component according to (6) or (7), wherein the crystallizer is provided with a stirrer in the apparatus and is maintained in a state in which the seed crystal flows. Processing equipment.

  In a normal crystallization treatment, if there are insufficient components among the components to be crystallized necessary for the crystallization reaction, the insufficient components are added as a crystallization agent. Even if the concentration of the crystallization target component is low, the concentration of the crystallization target component can be set to a concentration necessary for the crystallization reaction with the concentration. In addition, the crystallization product is separated and removed by the crystallizer, and the wastewater with a low concentration of the crystallization target is returned to the distillation concentrator. As a result, the amount of concentrated liquid generated is reduced and the concentrated liquid production waste disposal cost can be greatly reduced.

  An example of an embodiment of the present invention will be described in more detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments and examples.

An embodiment of the present invention is shown in the flowchart of FIG.
The treatment apparatus shown in FIG. 1 is composed of a distillation concentrating apparatus 1 and a crystallization apparatus 2, and waste water 11 containing a crystallization target component is condensed water 12 (treated water, in-site recycle) recovered by heat after evaporation in the distillation concentrating apparatus 1. Use) and concentrated drainage 13. A part 13A of the concentrated waste water 13 is drawn out of the system, and the remaining part is crystallized by the crystallizer 2 and circulated to the distillation concentrator 1 together with the waste water 11 containing the components to be crystallized. In addition, although not shown in figure, piping, a pump, etc. are suitably provided before and behind each apparatus, and each waste_water | drain flows in or out.

Here, a part of the concentrated waste water 13 whose concentration to be crystallized is increased by distillation is sent to the crystallizer 2. In the crystallization tank 2, seed crystals are flowing, in which the components to be crystallized in the concentrated waste water 13 react and precipitates.
Since the concentration of the component to be crystallized in the concentrated waste water 13 becomes higher as it is concentrated by distillation, the crystallization reaction is continued without adding crystallization chemicals. If there is a seed crystal in this reaction, a newly crystallized product is deposited on the surface of the seed crystal. Due to this characteristic, the crystallized product gradually grows, so that it becomes granular with good sedimentation properties, and it is possible to separate the crystallized product from the concentrated waste water in the crystallization tank. Thereafter, the concentrated drainage 14 in which the crystallization target component is reduced is circulated to the distillation concentration apparatus 1. In the crystallization reaction, since the solubility of the crystallized product is small, the recovery rate of the crystallized product is high, and the concentration of the crystallization target component in the concentrated drainage 14 coming out of the crystallization tank is higher than the concentration of the crystallization target component in the drainage 11. Also lower.

Since the concentration of the crystallization target component that causes the scale generation is reduced in the concentrated waste water 14, the generation of scale on the evaporation surface or the like in the distillation concentration apparatus 1 is suppressed, and the concentration rate of the concentrated waste water 13 is further increased. It becomes possible to raise.
In addition, the crystallization treatment can be achieved without adding a crystallization chemical as in the prior art, and a calcium softening agent such as sodium carbonate before distillation concentration is not required.

Moreover, FIG. 2 shows the flowchart which shows another embodiment of this invention, Comprising: By adding a pH adjuster, for example, an acid, to the waste_water | drain containing the crystallization target component which enters into the distillation concentration apparatus 1. FIG. The pH of the liquid in the distillation concentration apparatus 1 is adjusted to 4 to 7, and the pH is adjusted to 6 to 9 by adding a pH adjusting agent such as an alkali to the concentrated waste water 13 entering the crystallizer 2. Indicates.
FIG. 3 shows that when the concentrated drainage 13 entering the crystallization apparatus 2 has a part of the crystallization target component insufficient to cause the crystallization reaction to sufficiently proceed, the crystallization component ( The aspect which adds the chemical | medical agent for crystallization) 10 is shown.
In FIGS. 2 to 3, the numbers common to those in FIG. 1 mean that the configuration of the device or the like is the same.

  The evaporation unit of the distillation apparatus may be any type such as a horizontal tube type, a vertical tube type, a coil type, a stirring film type, a centrifugal thin film type, and a plate type, but it is desirable to be able to suppress scale adhesion. Especially when the evaporation surface is a metal surface, once the scale adheres to the evaporation surface, a new scale will continue to grow on the adhered scale, and the scale can only be dissolved by chemicals or peeled off by external force such as high pressure spray. There is a difficulty in that there is no method for removing from the evaporation surface. As a solution to such a problem, there is a distillation concentration method using a distillation concentration apparatus of the following form.

  In FIG. 5, the schematic block diagram of the distillation concentration apparatus 1 of this invention is shown. The distillation concentrating apparatus 1 includes a distillation concentrating apparatus main body 17 in which one or two or more bag-like thermoplastic synthetic resin thin film bags 16 (for example, polyethylene or polypropylene are used) are attached as evaporation surfaces inside the apparatus. A circulation pump 18 that supplies the waste water to be concentrated received in the main body of the distillation concentrator 1 to the evaporation surface, a self-vapor recompression fan or external steam heater 20 that compresses and evaporates the vapor evaporated by distillation, and depressurizes the evaporation surface. It is composed of a vacuum pump or ejector 21 (to make negative pressure). The waste water 11 containing the crystallization target component flows into the distillation concentration apparatus 1 main body. Here, the influent wastewater is mixed with the concentrated wastewater circulating in the main body, and is sent to the upper part of the main body of the apparatus 1 by the concentrated wastewater circulation pump 18, and is evenly distributed to each thermoplastic synthetic resin thin film bag 16 (inflow water equalizing distributor). 19) and flows down the outer surface of the thermoplastic synthetic resin thin film bag 16 and is concentrated by evaporation. The evaporated steam is compressed by a self-vapor recompression fan or an external steam heater 20, heated to about 1 to 5 ° C. by compression, and flows into the inner surface of the thermoplastic synthetic resin thin film bag 16. Here, the compressed steam releases heat from the inner surface of the thermoplastic synthetic resin thin film bag 16 to evaporate the concentrated waste water flowing on the surface of the thin film 16, and becomes clear condensed water in the thermoplastic synthetic resin thin film bag 16. This condensed water is discharged from the bottom nozzle (not shown) of the thermoplastic synthetic resin thin film bag 16 and reused in the field. There are a vacuum pump type and an ejector type in the pressure reducing system of the apparatus. Moreover, the distillation concentration apparatus 1 is operated at an internal pressure of 120 to 200 hPa.

  Scale generation is further suppressed by adjusting the concentrated drainage pH during distillation. In order to further suppress the generation of scale, the pH is adjusted to 4 to 7, preferably 5 to 6. As the pH is lowered from 7, it becomes a safe region where scales are less likely to be generated. However, considering the chemical cost for pH adjustment, the influence of fluctuations in the water quality of the drainage, etc., it is appropriate to make the above range. On the other hand, when the pH is higher than 7, the scale is easily generated. This pH adjustment measures the pH of the wastewater flowing into the distillation concentrator 1 or the concentrated wastewater circulating in the distillation concentrator 1, and equipment such as hydrochloric acid is used to lower the pH, and caustic soda is used to raise the pH. Inject in or near the device inlet.

  Since the synthetic resin thin film bag 16 is a synthetic resin, the scale does not easily adhere to the thin film bag, and the thin film thickness is 10 to 100 μm, preferably 40 to 60 μm, which is very thin. . For these reasons, the scale is less likely to adhere as compared with a general metal surface evaporation apparatus.

In FIG. 6, the schematic block diagram of the crystallizer of this invention is shown. The crystallizer comprises a crystallizer 22 filled with seed crystals, a stirrer 23, and a pH meter 24. The waste water 11 containing the crystallization target component is introduced into the inside of the cylindrical baffle plate 25 having no upper and lower surfaces of the crystallization tank 22, and new crystallized substances are formed on the seed crystal surface flowing by the stirrer 23. Precipitates and crystallized product 15 grows. The concentrated drainage 14 in which the crystallization target component has been reduced by the crystallization reaction rises outside the baffle plate and is discharged from the overflow port. Further, the crystallized product 15 is periodically pulled out so that the crystallized product concentration in the tank becomes constant. Furthermore, the pH in the tank is adjusted with a pH meter and an alkaline agent such as caustic soda to a pH range in which the precipitation reaction of the crystallized product easily occurs.
The residence time of the crystallization tank 22 is generally 30 to 180 minutes, the pH in the tank is 6 to 9, preferably 7 to 8, and the crystallized substance concentration in the tank is 20000 to 40000 mg / L (liter), although it varies depending on the crystallization target component. ). When the pH is less than 6, the crystallized product is difficult to precipitate, and when the pH exceeds 9, the crystallized product becomes fine, and the chemical cost for pH adjustment increases.

The seed crystal flow by the stirrer 23 can surely flow a seed crystal having a large particle size as compared with the conventional seed crystal flow by an upward water flow, and the seed crystal is fixed and loses fluidity. Can be prevented. In addition, since the seed crystal concentration can be maintained high, the apparatus can be made small, and stable crystallization treatment can be performed. The stirrer 23 includes a motor 26, a shaft 27, and blades 28. The blades 28 may have any shape as long as seed crystals can flow, such as paddles, propellers, and turbines. .
In the present invention, the waste water containing the crystallization target component includes waste water containing calcium and sulfuric acid, waste water containing calcium and fluorine, and the like, in addition to the exemplified waste water containing calcium and phosphoric acid. It is suitable when both components contain a component that forms a sparingly soluble salt.

  EXAMPLES In the following, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited by these examples.

Example 1
Experiments were performed using equipment equipped with the processing flow shown in FIG. The components to be crystallized in this experiment are calcium and phosphorus, and the crystallized product is hydroxyapatite phosphate (hereinafter referred to as “HAP”). The reaction formula in this crystallization reaction is shown by the following (1).
10Ca ²⁺ + 6PO ₄ ^3- + 2OH ⁻ → Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ (1)
The processing flow shown in FIG. 4 is the same as the processing flow shown in FIG. 1, but the waste water 3 to be treated is waste water containing calcium and phosphoric acid. HAP7 is shown as condensed water 4, concentrated drainage 5, and concentrated drainage 6 with reduced calcium.
Since the concentration of calcium ions and phosphate ions in the concentrated waste water 5 increases as the concentration is increased by distillation, the HAP crystallization reaction is continued without adding calcium-based chemicals. If there is a HAP seed crystal during this reaction, newly crystallized HAP is deposited on the surface of the seed crystal. Due to this characteristic, the HAP crystallized product gradually grows, so that it becomes granular with good sedimentation, and the solid-liquid separation of the crystallized product and the concentrated waste water becomes possible in the HAP crystallizer. Thereafter, the concentrated drainage 6 with reduced calcium ions is circulated to the distillation concentrating device 1. In the HAP crystallization reaction, since the solubility of HAP is small, the calcium concentration in the concentrated drainage 6 coming out of the HAP crystallization tank is lower than the calcium concentration in the drainage 3.

A continuous test was conducted in which the biologically treated water of the mixed wastewater of human waste and septic tank sludge shown in Table 2 was distilled and concentrated under the conditions shown in Table 3. The amount of concentrated drainage withdrawn was adjusted so that the concentrated wastewater concentration ratio would be a predetermined ratio. A part of the concentrated wastewater was allowed to flow into the HAP crystallizer, HAP was precipitated, and the HAP crystallized product was settled and separated, and then the concentrated wastewater with reduced calcium was circulated through the distillation concentrator. After the test, the state of scale adhesion in the distillation concentration apparatus was confirmed. By this test, the results shown in Table 1 were obtained. By separating and reducing calcium ions in the concentrated wastewater by HAP crystallization, the concentrated wastewater could be concentrated up to 7 times without depositing scale in the distillation concentration apparatus. On the other hand, in the comparative example (conventional example), when the concentrated wastewater was circulated without HAP treatment, when the concentrated wastewater was concentrated up to 3 times, a large amount of scale adhered to the distillation concentrator. The test results are shown in Table 1.
Table 2 shows the water quality results of the distillation and concentration performed in Example 1 (the present invention).

ADVANTAGE OF THE INVENTION According to this invention, a concentration magnification can be raised, suppressing the calcium system scale generation | occurrence | production adhesion | attachment in a distillation concentration apparatus. Therefore, the amount of concentrated drainage can be reduced to about 1/3 of the conventional amount, and the waste disposal cost can be greatly reduced.
In addition, the water quality of the condensed water (treated water) by the distillation treatment of the present invention is clear with no BOD, COD, SS, chromaticity, and evaporation residue, and can be reused as industrial water in the field. become.

Particularly in the HAP crystallization treatment, calcium necessary for the HAP crystallization reaction is added as a calcium-based chemical. However, in the present invention, since the HAP crystallization reaction is continued by utilizing the fact that the calcium ion concentration increases with concentration, it is not necessary to add calcium-based chemicals.
Furthermore, the HAP generated by the HAP crystallization reaction can be reused as a phosphate fertilizer, that is, a valuable material, and the waste disposal cost of the calcium carbonate sludge generated by the conventional calcium softening treatment can be eliminated.

  Since the present invention can treat wastewater containing crystallization target components such as sewage, human waste, and industrial wastewater without adding calcium softening chemicals or crystallization additive chemicals, sewage treatment plants and various wastewater treatment facilities. The use in etc. is expected.

It is a figure which shows the processing flow of this invention. It is a figure which shows the processing flow of this invention using a pH adjustment means. It is a figure which shows the processing flow of this invention which adds the chemical | medical agent for crystallization. It is a figure which shows the processing flow in the Example of this invention. In the processing apparatus of this invention, it is a figure which shows schematic structure of the distillation concentration apparatus. In the processing apparatus of this invention, it is a figure which shows schematic structure of a crystallization apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Distillation concentration apparatus 2 Crystallization apparatus 3 Waste water containing calcium and phosphoric acid 4 Condensed water 5 Concentrated waste water 6 Concentrated waste water with reduced calcium 7 HAP crystallization product 8 Acid 9 Alkali 10 Crystallizing chemical 11 Including waste water 12 Condensed water (treated water, reuse in the field)
13 Concentrated wastewater 13A Concentrated wastewater (outside the system)
14 Concentrated wastewater with reduced crystallization target components 15 Crystallized product (outside system)
16 Thermoplastic Synthetic Resin Thin Film Bag 17 Distillation Concentrator Main Body 18 Concentrated Drain Circulation Pump 19 Inflow Water Equal Distributor 20 Self Steam Recompression Fan (or External Steam Heater)
21 Vacuum pump (or ejector)
22 Crystallization tank 23 Stirrer 24 pH meter 25 Baffle plate 26 Motor 27 Stirrer shaft 28 Stirrer blade 29 Alkali

Claims (8)

  The waste water containing the crystallization target component mixed with the concentrated effluent from which the concentration of the crystallization target component from the subsequent crystallization step is reduced is introduced into the distillation concentration step and concentrated by distillation. The vapor generated by the distillation is condensed water. Concentrated wastewater obtained by distillation and concentration is partially taken out of the system, the rest is introduced into the crystallization step for crystallization, the crystallization product is taken out, and the concentration of crystallization target components from the crystallization step A method for treating wastewater containing a crystallization target component, characterized in that the concentrated wastewater reduced in water is circulated to mix with the wastewater containing the crystallization target component.   By adjusting the pH of the mixed water of the waste water containing the crystallization target component and the concentrated waste water having a reduced concentration of the crystallization target component, the pH of the liquid in the distillation concentration step is set to 4 to 7, and the crystallization step The method for treating wastewater containing a crystallization target component according to claim 1, wherein the pH of the liquid in the crystallization step is adjusted to 6 to 9 by adjusting the remaining pH of the concentrated wastewater that enters.   The method for treating wastewater containing a crystallization target component according to claim 1 or 2, wherein a crystallization chemical is added to the concentrated wastewater entering the crystallization step.   In the said crystallization process, the water level of a crystallizer is maintained constant, and the crystallized material storage amount in a crystallizer is managed with a load cell, The any one of Claims 1-3 characterized by the above-mentioned. A method for treating wastewater containing components to be crystallized.   The crystallization target component according to any one of claims 1 to 4, wherein the crystallized product is at least one of calcium phosphate, calcium hydrogen phosphate, phosphate apatite, calcium fluoride, and calcium sulfate. Wastewater treatment method including.   Distillation that removes the vapor generated by distillation as condensed water by introducing mixed water mixed with waste water containing the target component for crystallization and concentrated waste water with reduced concentration of target component for crystallization from the subsequent crystallizer. Concentrated wastewater from the concentrating device and the distillation concentrating device, partly discharged from the piping for discharging out of the system, the rest is introduced into the crystallization device from the piping to be crystallized, and has a crystallized material extraction tube. A crystallization target component comprising: a crystallization apparatus; and a pipe that circulates a concentrated waste water in which the concentration of the crystallization target component of the crystallization apparatus is reduced to an introduction pipe of the waste water containing the crystallization target component. Wastewater treatment equipment.   7. The apparatus for treating wastewater containing a crystallization target component according to claim 6, wherein the distillation concentrating apparatus has a thermoplastic synthetic resin thin film as an evaporation surface.   The apparatus for treating wastewater containing a crystallization target component according to claim 6 or 7, wherein the crystallization apparatus is provided with a stirrer in the apparatus and maintained in a state in which seed crystals flow.

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