JP2014014738A - Method and apparatus for treating organic wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce a hypochlorous acid solution by electrolytically treating concentrated water which is obtained by performing a salt removal treatment of organic wastewater containing salts and organic matter.SOLUTION: A sodium hypochlorite solution is generated by performing a first softening treatment, an SS removal treatment, and a salt removal treatment of organic wastewater containing salts and organic matter, again performing a softening treatment of the obtained concentrated salt water, and electrolytically treating the obtained second softening treatment water.

Description

  The present invention relates to a method and an apparatus for treating organic wastewater containing salt at a high concentration such as leachate and leachate leached from waste landfill.

  Organic wastewater such as human waste and leachate from landfills generally contain high concentrations of pollutants such as salts and organic substances such as calcium ions and chlorine ions. Such organic wastewater has a high biochemical oxygen demand (hereinafter referred to as BOD) and chemical oxygen demand (hereinafter referred to as COD), and also contains many suspended solids (hereinafter referred to as SS). Therefore, the organic wastewater cannot be reused as it is or discharged directly into a river or the like.

  Such organic wastewater treatment methods include, for example, biological treatment for the purpose of removing BOD, coagulation sedimentation treatment for the purpose of removing chromaticity, COD and SS, and sand for the purpose of removing turbidity such as SS. Filtration, microfiltration (referred to as “MF”) membrane treatment, and the like are known. However, these treatments could remove organic components in the organic wastewater, but could not effectively remove salts such as calcium ions and chlorine ions.

  Therefore, conventionally, as a method for treating organic wastewater containing salts, after performing softening treatment on organic wastewater containing salts to reduce the calcium concentration therein, biological treatment, coagulation sedimentation treatment, sand filtration treatment, One or more treatments selected from the group consisting of MF membrane treatment or a treatment consisting of a combination of two or more are performed, and then desalted by RO membrane treatment using a reverse osmosis membrane (hereinafter referred to as “RO membrane”), Separated into RO concentrated water and RO treated water, the RO treated water is recovered and, on the other hand, the RO concentrated water is subsequently subjected to electrodialysis (hereinafter referred to as “ED”) treatment, and then ED concentrated water and ED treated water. The ED treated water is returned to the supply side of the RO membrane treatment, while the ED concentrated water is separated into water and salts by evaporating and drying, and the organic waste water is isolated. The processing method of Is (Patent Document 1).

Japanese Patent No. 3800449

  The treatment method proposed in Patent Document 1 described above is a method of separating concentrated water obtained by ED treatment into water and salts by evaporating and drying to isolate the salts. However, in the evaporative drying treatment, enormous heat of evaporation is required to evaporate and dry the ED concentrated water having a high salt concentration into a solid salt, which has been a main cause of an increase in running cost. Moreover, since the collected solid salts are not a single component, the use of the obtained dry salts is limited, and in reality, the collected solids are stored for a long period of time or landfilled again at the final disposal site. I also had the problem of having to do it.

  Therefore, when an attempt was made to produce a hypochlorous acid solution by electrolytic treatment of the concentrated water obtained by ED treatment, scale deposition derived from calcium and magnesium occurred in the electrolytic treatment apparatus, which inhibited stable electrolytic treatment. A new challenge has been revealed. Moreover, since the concentrated chlorine obtained by ED treatment is subjected to electrolytic treatment as it is to produce a hypochlorous acid solution, the effective chlorine concentration cannot be stabilized. It has become clear that this is difficult.

  In the method for treating organic wastewater having a high salt concentration, the present invention provides a calcium hypochlorite solution by electrolytic treatment of concentrated treated water obtained by performing salt removal treatment such as ED treatment or RO treatment. The primary purpose is to suppress the precipitation of magnesium-derived scale and to perform stable electrolytic treatment, and to stabilize the effective chlorine concentration of the hypochlorous acid solution obtained by the electrolytic treatment. This is the second purpose.

In order to solve this problem, the present invention provides a first softening treatment step for reducing the calcium concentration by performing softening treatment on organic wastewater containing salts and organic matter, biological treatment, coagulation sedimentation treatment, activated carbon adsorption treatment. An SS removal treatment step consisting of one or more treatments selected from the group consisting of sand filtration treatment and MF membrane treatment or a combination of two or more,
After performing the first softening treatment step and the SS removal treatment step,
An ED treatment step that separates into ED concentrated water and ED treated water by ED treatment, an RO membrane treatment step that separates into RO concentrated water and RO membrane treated water by RO membrane treatment, and nanofiltration (hereinafter referred to as “NF”) ) A salt removal treatment step including any step or two or more types of NF membrane treatment steps separated into NF membrane concentrated water and NF membrane treated water by membrane treatment;
The salt concentration water obtained in the salt removal step, that is, the ED concentration water, the RO concentration water, or the NF membrane concentrated water is subjected to a second softening treatment step of performing a softening treatment to reduce the calcium concentration, Proposed is a method for treating organic wastewater, characterized by carrying out an electrolytic treatment step of electrolyzing the second softening treatment water obtained in the second softening treatment step to produce a sodium hypochlorite solution.

  The present invention also proposes that in the electrolytic treatment step, electrolysis is performed by adjusting the pH of the water to be treated to 10 or higher, or the pH of the electrolytically treated water after the electrolysis is adjusted to 10 or higher. . Further, at this time, it is further proposed to carry out a storage step of maintaining the pH of the electrolyzed water after electrolysis obtained in the electrolysis step at 10 or more.

  According to the organic wastewater treatment method proposed by the present invention, with respect to organic wastewater containing salts, the calcium concentration is lowered in the first softening treatment step, and organic substances and SS are removed in the SS removal treatment step. After reducing the organic matter by the above (the softening treatment and SS removal treatment are collectively referred to as the “pretreatment step”), and the salt removal step is performed, the water recovery rate of the RO membrane treatment decreases due to the influence of SS and organic matter. And leakage of organic components into the ED treated water can be prevented. Therefore, according to this method, organic wastewater containing a high concentration of salts can be efficiently desalinated and recovered as salt removal treated water, which can be reused or directly discharged into rivers, etc. Can do.

  Even if the concentration of calcium or magnesium is lowered to a level sufficient for release into rivers or the like in the first softening treatment step, the concentration of calcium or magnesium in the salt-enriched water is increased again after being concentrated in the salt removal step. It has been found that scale deposition derived from calcium and magnesium occurs in the electrolytic treatment apparatus, which is a cause of hindering stable electrolytic treatment. Therefore, when the second softening treatment was performed on the salt concentrated water obtained in the salt removal step to reduce calcium and the like, it was possible to suppress the precipitation of calcium and magnesium-derived scale in the electrolytic treatment apparatus, and it was stable. Electrolytic treatment can be carried out.

Furthermore, when preparing a hypochlorous acid solution by electrolysis, the pH of the water to be treated (second softened water) obtained by performing the second softening treatment is adjusted to 10 or higher, or electrolysis is performed, or When the pH of the electrolyzed water after electrolysis was adjusted to 10 or more, the effective chlorine concentration could be stabilized, and a hypochlorous acid solution could be produced industrially stably.
In addition, when the pH is adjusted in this way, when the obtained electrolytically treated water is stored, it is stored so that the pH is maintained at 10 or more, so that effective chlorine of hypochlorous acid is also stored during storage. It became possible to stabilize the concentration.

It is the schematic which showed an example of the processing method of organic wastewater, and an example of the organic wastewater processing apparatus for implementing it. It is the schematic which showed an example of the processing method of organic wastewater, especially the example which showed the salt removal processing process in detail, and an example of the organic wastewater treatment apparatus for implementing it. It is the schematic which showed the example of the change of the processing method of the organic wastewater shown in FIG. 2, and an example of the organic wastewater treatment apparatus for implementing it. It is the schematic which showed an example of the salt removal processing process different from FIG. 2, and an example of the organic waste water treatment apparatus for implementing it. It is the schematic which showed the example of the change of the processing method of the organic wastewater shown in FIG. 4, and an example of the organic wastewater treatment apparatus for implementing it. It is the schematic which showed an example of the electrolytic processing apparatus. It is the schematic which showed another example of the electrolytic processing apparatus. It is the schematic which showed an example of the storage process of the produced | generated electrolytic treatment water. 6 is a graph showing changes in effective chlorine concentration of electrolytically treated water in Example 1 and Reference Example 1. 3 is a graph showing the progress of current efficiency in electrolytic treatment in Example 1 and Comparative Example 1. 6 is a graph showing changes in effective chlorine concentration of electrolytically treated water in Example 3.

  Next, an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.

[Organic wastewater treatment equipment 1]
FIG. 1 is a schematic diagram illustrating an example of an organic wastewater treatment method A as an example of an embodiment of the present invention and an organic wastewater treatment apparatus 1 for implementing the method. However, the apparatus for implementing the organic wastewater treatment method A is not limited to this apparatus.

  In the organic wastewater treatment apparatus 1, as shown in FIG. 1, a to-be-treated water inflow pipe 2 for supplying organic wastewater is connected to a first softening treatment apparatus 3. 1 SS removal treatment device 5 is connected via the softened treated water supply pipe 4, and a salt removal treatment device 7 is connected to the outlet side of the SS removal treatment device 5 via the SS removal treatment water supply pipe 6 to remove the salt. A salt concentrated water supply pipe 8 and a salt removal treated water discharge pipe 9 are connected to the outlet side of the processing apparatus 7. The salt concentrated water supply pipe 8 is connected to a second softening processing apparatus 11, and the second softening processing apparatus 11. An electrolytic treatment apparatus 13 is connected to the outlet side of the electrolytic treatment apparatus via a second softened treated water supply pipe 12, and sodium hypochlorite is connected to the outlet side of the electrolytic treatment apparatus 13 via a sodium hypochlorite solution supply pipe 14. A solution storage tank 15 is connected.

The SS removal treatment device 5 is configured by combining one or more devices selected from the group consisting of biological treatment devices, coagulation sedimentation treatment devices, activated carbon adsorption treatments, sand filtration treatment devices, and MF membrane treatment devices, or two or more devices. Just do it.
For example, by connecting an agglomeration microfiltration device to the outlet side of the biological treatment device, water in which an inorganic flocculant or the like is added to the biological treatment water to form an aggregate can be filtered through the MF membrane.

The salt removal processing device 7 may be configured by any one of an ED processing device, an RO membrane processing device, and an NF membrane processing device, or a combination of two or more of these devices. As an example of the configuration of the salt removal treatment device 7, for example, as shown in FIG. 2, an RO membrane treatment device 16 is connected to the outlet side of the SS removal treatment device 5 via an SS removal treatment water supply pipe 6, and the RO membrane treatment is performed. The RO concentrated water supply pipe 17 and the RO membrane treated water discharge pipe 18 are connected to the outlet side of the apparatus 16, the RO concentrated water supply pipe 17 is connected to the ED processing apparatus 19, and the ED processing is connected to the outlet side of the ED apparatus 19. A configuration example in which the water supply pipe 20 and the ED concentrated water supply pipe 21 are connected and the ED concentrated water supply pipe 21 is connected to the second softening treatment device 11 can be given.
At this time, for example, as shown in FIG. 3, the ED treated water supply pipe 20 is connected to the treated water inflow pipe 2, the softened treated water supply pipe 4 or the SS removal treated water supply pipe 6, and the ED treated water is treated. It can also be configured to return to the water inflow pipe 2, the softened treated water supply pipe 4 or the SS removal treated water supply pipe 6.

As another configuration example of the salt removal treatment device 7, for example, as shown in FIG. 4, an ED device 19 is connected to the outlet side of the SS removal treatment device 5 via the SS removal treated water supply pipe 6, and the ED device. 19, an ED treated water supply pipe 20 and an ED concentrated water supply pipe 21 are connected to each other, the ED concentrated water supply pipe 21 is connected to the second softening treatment apparatus 11, and the ED treated water supply pipe 20 is an RO membrane. A configuration example in which the RO concentrated water supply pipe 17 and the RO membrane treated water discharge pipe 18 are connected to the processing apparatus 16 and the outlet side of the RO membrane processing apparatus 16 can be given.
At this time, for example, as shown in FIG. 5, the RO concentrated water supply pipe 17 is connected to the treated water inflow pipe 2, the softened treated water supply pipe 4, or the SS removal treated water supply pipe 6. It can also be configured to return to the inlet pipe 2, the softened treated water supply pipe 4 or the SS removed treated water supply pipe 6.

  Furthermore, instead of the RO membrane device 16, an NF membrane treatment device can be installed.

  Each of the above devices may be connected by various treated water supply pipes, or a tank may be provided at an appropriate location to temporarily store the treatment liquid and supply it from there to each device. Good. Other processing apparatuses can be provided as appropriate.

[This processing method A]
The organic wastewater treatment apparatus 1 can be used to implement the organic wastewater treatment method A.

  As shown in FIG. 1, organic wastewater treatment method A (referred to as “this treatment method A”) reduces the calcium concentration by performing a first softening treatment on organic wastewater containing salts and organic matter. (1st softening treatment process), SS removal treatment consisting of one or more treatments selected from the group consisting of biological treatment, coagulation sedimentation treatment, activated carbon adsorption treatment, sand filtration treatment, MF membrane treatment, or a combination of two or more is performed. (SS removal treatment step) Next, the salt removal treatment is performed to reduce the salt concentration to obtain the salt removal treatment water, and the salt concentration water in which the salt is concentrated is obtained (salt removal treatment step), and the salt removal treatment While recovering water, the salt-enriched water is subjected to a second softening treatment to reduce calcium concentration and magnesium concentration (second softening treatment step), and then treated water obtained by the second softening treatment. ("Second The salt removal treatment described above is carried out by carrying out a series of treatment methods in which an electrolysis is performed by supplying a water treatment solution (also referred to as “chemical treatment water”) to electrolyze and a sodium hypochlorite solution is produced (electrolysis treatment step). In this method, water and the sodium hypochlorite solution are recovered.

<Treatment water>
The treated water of this treatment method A may be any organic wastewater that contains salts and organic matter and cannot be reused or discharged into rivers. For example, organic wastewater with a high salt concentration such as seawater, human waste, and leachate from landfills of garbage can be mentioned. These generally contain high concentrations of pollutants such as salts such as calcium ions and chlorine ions and organic substances.
From the viewpoint of further enjoying the effect of the present treatment method A, the chlorine ion concentration of the water to be treated is preferably 2000 to 20000 mg / L, more preferably 5000 mg / L or less, and most preferably 4000 mg / L or less. preferable.
Further, the evaporation residue component concentration (hereinafter referred to as “TDS”) of the water to be treated is preferably 4000 to 40000 mg / L.

<First softening process>
The first softening treatment reduces the hard water component (slightly soluble salt forming component) of calcium and magnesium in water by alkali precipitation such as lime soda softening method, ion exchange hard water softening method, chelating agent adsorption method, etc. And a process for obtaining softened water.

The lime soda softening method is a method of removing hardness by reducing calcium concentration by precipitating calcium as calcium carbonate using slaked lime (calcium hydroxide) or slaked lime and soda ash (sodium carbonate) together. .
The ion exchange method is a method of removing hardness components with an ion exchange resin.

The chelating agent adsorption method is a method of adsorbing calcium or magnesium hard water components (hardly soluble salt forming components) to the chelating agent.
Examples of the chelating agent include ethylenediaminetetraacetic acid salt (hereinafter referred to as “EDTA”), aminocarboxylic acid-based chelating agents such as diethylenetriaminepentaacetic acid and iminodiacetic acid, hydroxyethylethylenediaminetriacetic acid, dihydroxyethylethylenediaminediacetic acid), 1 , 3-propanediaminetetraacetic acid, or one or more of them selected from the group. Among them, it is preferable to use a chelating agent that can selectively adsorb and remove divalent metal ions such as iminodiacetic acid.

  In the first softening treatment step, it is only necessary to reduce the amount of Ca and Mg in the recovered treated water, that is, the softened treated water, to such an extent that scale generation due to hardness components of Ca and Mg can be suppressed. In that sense, if the amount of Ca or Mg is excessively reduced, the processing efficiency is lowered, which is not preferable economically. From this viewpoint, it is preferable to employ the lime soda softening method among the above treatments.

  Moreover, in a 1st softening process, it is preferable to process so that T-Ca density | concentration in softening process water may be 100 mg / L or less, especially 50 mg / L or less from the above viewpoints. However, there is no need to reduce the T-Ca concentration to less than 10 mg / L because it is sufficient that the scale generation due to the hardness components of Ca and Mg can be suppressed.

  Here, the “T-Ca concentration” is the total calcium concentration in water and includes not only ions but also dissolved and undissociated calcium salts. It is preferable that the T-Ca concentration is 100 mg / L or less because calcium scales can be effectively prevented from being generated in the RO membrane treatment process or the ED treatment process.

<SS removal treatment process>
The SS removal treatment step is a treatment step for removing SS such as organic pollutants from the softened water obtained in the step by biological treatment, coagulation sedimentation treatment, activated carbon adsorption treatment, sand filtration treatment, MF membrane treatment, etc. is there.
SS in the SS removal treatment solution is preferably 5 mg / L or less, and more preferably 1 mg / L or less.

  Specific examples of biological treatment include biological activated nitrification and denitrification in addition to the standard activated sludge method. By using these methods, organic substances are decomposed and nitrogen is removed. And SS and BOD can be reduced.

The coagulation-precipitation process is a process that forms fine flocculent substances and colloidal substances in water with flocculants to form flocs (aggregates), and if necessary, further increases the flocs with a polymer flocculant and solid-liquid separation. Alternatively, it is a treatment method in which ionized heavy metals are chemically reacted with a flocculant such as a chelating agent to precipitate and remove. SS, heavy metal ion components, and the like can be removed by the coagulation precipitation treatment. COD can also be lowered.
By performing biological treatment prior to the coagulation sedimentation treatment, the amount of coagulant added is small, and the treatment efficiency can be increased.

The activated carbon adsorption treatment is a treatment for adsorbing organic substances in water to activated carbon produced from bituminous coal or coconut shell. The adsorptive power of activated carbon varies depending on the type of organic substance, and it can remove soluble organic substances, COD, chromaticity, surfactants, odor components, and the like.
For example, it can be used as an adsorption tower or regeneration furnace for granular coal.
For the purpose of performing advanced treatment after biochemical treatment and recycling of secondary treated water, activated carbon adsorption treatment can also be used as pretreatment for chlorine disinfection.

Sand filtration is a filtration method that removes impurities by passing water to be treated through a sand filtration pond formed by laminating various layers of sand on a support gravel layer loaded with gravel, such as SS, Iron and manganese can be removed.
It is particularly effective to perform the coagulation sedimentation treatment as the SS removal treatment of the sand filtration treatment.

  Agglomeration precision membrane filtration (hereinafter referred to as “aggregation MF membrane filtration”) is a treatment method using an MF membrane, and preferably in combination with biological treatment, an inorganic flocculant is added to the treated water by biological treatment. It is good to filter what was made to pass with a MF membrane. When such a method is used, particularly SS can be removed from wastewater.

<Salt removal treatment process>
The salt removal treatment step includes an ED treatment step for separating ED concentrated water and ED treated water by ED treatment, an RO membrane treatment step for separating RO concentrated water and RO membrane treated water by RO membrane treatment, and an NF membrane treatment. The salt-removed treated water having a low salt concentration through any of the NF membrane treatment steps that are separated into NF membrane concentrated water and NF membrane treated water or a combination of two or more of these steps. And a salt-enriched water in which the salt is concentrated.

For example, as shown in FIG. 2, after SS removal treatment, desalination treatment is performed by RO membrane treatment to separate RO concentrated water and RO membrane treated water (reverse osmosis membrane treatment step), and RO membrane treated water. On the other hand, the RO concentrated water is subjected to ED treatment and desalted, and separated into ED concentrated water and ED treated water (electrodialysis treatment step), and the ED treated water is recovered and the ED concentrated water is recovered. May be supplied to the second softening treatment step.
At this time, as shown in FIG. 3, the ED treated water may be returned to the supply side of the first softening step, the SS removal treatment step, or the RO membrane treatment step.

For example, as shown in FIG. 4, after performing SS removal treatment, ED treatment is performed, desalting treatment is performed to separate ED concentrated water and ED treated water (ED treatment step), and the ED concentrated water is While supplying to the second softening treatment step, the ED treatment water is subjected to RO membrane treatment and desalted to separate into RO concentrated water and RO membrane treated water (RO membrane treatment step), RO membrane treated water and RO What is necessary is just to collect concentrated water.
At this time, as shown in FIG. 5, the RO concentrated water may be returned to the supply side of the first softening step, the SS removal treatment step, or the RO membrane treatment step.

  Although the order of the ED treatment process and the RO membrane treatment process does not matter, as shown in FIGS. 2 and 3, when the RO membrane treatment is performed on the treated water first, the salt concentration of the treated water If it is high, the osmotic pressure increases and the operating pressure on the RO membrane increases. Usually, since the operating pressure of the RO membrane is 6 MPa, if the salt concentration of the water to be treated is high, the amount of permeated water is lowered, leading to a reduction in the water recovery rate, making it difficult to ensure the stability of the treated water amount. In addition, when the mixed water of SS removal treated water and ED treated water is treated water for RO membrane treatment, if the concentration of organic matter in treated water is high, organic matter accumulates in the RO membrane supply liquid, and RO Organic matter contamination on the membrane increases, which may cause a reduction in permeation rate. For these reasons, when the RO membrane treatment is performed first, when the organic matter concentration and the salt concentration of the water to be treated are relatively low, specifically, the chlorine ion concentration is 2000 to 20000 mg / L or less, particularly 5000 mg / L. In the following, it is even more effective to use organic wastewater of 4000 mg / L or less as treated water. In terms of TDS, it is more effective to use organic waste water of 4000 to 40,000 mg / L or less, particularly 10,000 mg / L or less, especially 8000 mg / L or less as the water to be treated. According to the RO membrane treatment, organic substances and salts can be more effectively removed, and a final treatment liquid with higher water quality can be obtained.

On the other hand, as shown in FIGS. 4 and 5, when the ED treatment is first performed on the water to be treated, the water to be treated for the RO membrane treatment is only the ED treated water. Since the salt concentration of treated water is also low, the water recovery rate in RO membrane treatment can be increased. In such a point, the difference in the effect becomes more remarkable as the salt concentration and the chlorine ion concentration of the organic wastewater are higher.
At this time, by returning the RO membrane concentrated water to the supply side of the ED treatment, the chlorine ion concentration in the ED concentrated water can be increased, and the amount of sodium hypochlorite solution produced by the electrolytic treatment can be increased. it can.
For this reason, when permeation is first performed by ED treatment, when the organic matter concentration and the salt concentration of the water to be treated are relatively high, specifically, the chlorine ion concentration is 5000 mg / L or more, particularly 10,000 mg / L. Above all, it is even more effective to use organic wastewater of 20000 mg / L or more as treated water. In terms of TDS, organic wastewater is 10,000 mg / L or more, especially 20000 mg / L or more, especially 40000 mg / L or more. It is more effective to use wastewater as treated water.

  Note that the same effect can be obtained by performing NF membrane treatment instead of the RO membrane treatment.

(RO membrane treatment)
The RO membrane treatment is a method of separating the RO concentrated water and the RO membrane treated water by applying a mechanical pressure equal to or higher than the osmotic pressure to the salt water in the chamber partitioned by the RO membrane and passing the RO membrane.

  It is known that the efficiency of RO membrane treatment is improved when the salt concentration is low. Therefore, the treated water desalted by the ED treatment in the next step is returned to the treated water inflow pipe 2, the softened treated water supply pipe 4 or the SS removed treated water supply pipe 6 as shown in FIG. If the water to be treated is reduced, the salt concentration of the water to be treated supplied to the RO membrane treatment device 16 is reduced compared to the case where the water is not returned. Therefore, the RO membrane treatment is performed in a state where the salt concentration is lower than that of normal waste water. Accordingly, the RO membrane treated water having a very low salt concentration can be efficiently recovered. In addition, high-concentration RO concentrated water can be collected in a reduced volume, and the electrodialysis treatment in the next step can be performed on such a reduced volume of RO concentrated water, which is a quantitative measure of ED treatment. The burden can be reduced.

The desalting rate in the RO membrane treatment is preferably 80% or more, more preferably 85% or more, and particularly preferably 98% or more. The TDS of RO concentrated water is preferably 15000 mg / L or more, and more preferably 25000 mg / L or more.
Here, “TDS” refers to a component that remains in the evaporator as a solid component when the water content of the water is evaporated.

(ED processing)
In ED processing, a large number of ED membranes are arranged, RO concentrated water is supplied to the alternately formed concentration chamber and dilution chamber, energized to obtain high concentration ED concentrated water in the concentration chamber, and low concentration in the dilution chamber. This is a method for obtaining ED treated water.

The desalting rate in ED treatment is preferably 80% or more, and more preferably 95% or more.
The TDS of ED treated water is preferably 6000 mg / L or less, and more preferably 5000 mg / L or less.
The TDS in the ED concentrated water after the ED treatment is preferably 100,000 mg / L or more, and the chlorine ion concentration is preferably 50,000 mg / L or more.

  In the ED treatment, in order to suppress the generation of scale derived from Ca and Mg remaining in the treated water of the SS removal treatment, the pH is preferably 7 or less, particularly 5 or less.

If the treated water desalted by the ED treatment is returned to the treated water inflow pipe 2, the softened treated water supply pipe 4 or the SS removed treated water supply pipe 6, as shown in FIG. Since the salt concentration of the treated water to be supplied is reduced, it is possible to improve the processing efficiency of the RO membrane treatment and to collect the high concentration RO concentrated water in a reduced volume. A reduced volume of RO concentrated water can be used as a target, and the quantitative burden of ED processing can be reduced.
In particular, by returning the treated water desalted by the ED treatment to the softened treated water supply pipe 4, it is possible to decompose the residual organic matter by performing SS removal treatment, particularly biological treatment, and further reduce the organic matter. Can do. The treated water after ED treatment is greatly reduced in salt concentration. However, organic substances that are nonionic cannot be removed by the ED treatment and remain in the treated water. These are disassembled and removed by returning them to the pretreatment step.

(NF membrane treatment)
In addition, it is also possible to perform NF film | membrane process instead of RO film | membrane process. As an apparatus, an NF membrane treatment apparatus can be installed instead of the RO membrane treatment apparatus.

The RO membrane used for the RO membrane treatment has a pore size of approximately 2 nm or less and allows water to pass therethrough but does not permeate impurities other than water such as ions and salts.
On the other hand, the nanofilter used for the NF membrane treatment has a pore size of about 1 nm to 2 nm and a blocking rate of ions and salts of about 70% or less. However, the form, principle, and usage are the same as for the RO membrane.

  When the salt concentration of the water to be treated becomes high, the RO membrane needs to be filtered by applying a high pressure by increasing the thickness of the membrane or continuously passing a plurality of membranes. On the other hand, the NF membrane has a small burden even if the salt concentration of the water to be treated is high. Therefore, when the salt concentration of the water to be treated is not so high and the organic matter concentration is high, it is preferable to perform the NF membrane treatment to increase the water recovery rate.

<Second softening process>
In the second softening treatment step, for example, alkali precipitation such as lime soda softening method, ion exchange hard water softening method, chelating agent adsorption method or the like, calcium or magnesium hard water components in the salt-concentrated water obtained in the above step This is a treatment step in which (softly soluble salt forming component) is reduced to obtain second softened treated water.

The lime soda softening method is a method of removing hardness by reducing calcium concentration by precipitating calcium as calcium carbonate using slaked lime (calcium hydroxide) or slaked lime and soda ash (sodium carbonate) together. .
The ion exchange method is a method of removing hardness components with an ion exchange resin.

The chelating agent adsorption method is a method in which a hard water component (a hardly soluble salt forming component) of calcium or magnesium is adsorbed to a chelating agent capable of selectively adsorbing bivalent or higher-valent metal ions.
Examples of the chelating agent include ethylenediaminetetraacetic acid salt (hereinafter referred to as “EDTA”), aminocarboxylic acid-based chelating agents such as diethylenetriaminepentaacetic acid and iminodiacetic acid, hydroxyethylethylenediaminetriacetic acid, dihydroxyethylethylenediaminediacetic acid), 1 , 3-propanediaminetetraacetic acid, or one or more of them selected from the group. Among them, it is preferable to use a chelating agent that can selectively adsorb and remove divalent metal ions such as iminodiacetic acid.

  In the second softening treatment, the T-Ca concentration in the second softening treatment water is reduced from the viewpoint of enabling stable electrolytic treatment by suppressing the precipitation of calcium and magnesium-derived scale in the electrolytic treatment step. It is preferable to perform the treatment so that the T-Mg concentration is less than 10 mg / L and the T-Mg concentration is less than 5 mg / L. Especially, if both Ca and Mg density | concentration shall be 1 mg / L or less, more stable electrolytic treatment can be performed.

In the second softening treatment step, it is preferable to employ a chelating agent adsorption method among the above treatments in order to effectively reduce the T-Ca and T-Mg concentrations in the second softening treatment water as described above.
However, when the Ca and Mg concentrations of ED concentrated water are as high as 100 mg / L or more, the softening treatment by alkali precipitation + filtration treatment is relatively low cost, which is preferable.
On the other hand, when the ED concentrated water Ca and Mg concentrations are relatively low at 100 mg / L or less, the chelate adsorption treatment can be made compact, and both Ca and Mg can be removed at a low concentration, which is a preferable treatment method.

<Electrolytic treatment process>
The electrolytic treatment step is a treatment step for producing a sodium hypochlorite solution by electrolyzing the second softened water obtained in the above step.

However, if a hypochlorous acid solution is produced by electrolytic treatment with the second softened water obtained in the above process as it is, the effective chlorine concentration is not stabilized and a hypochlorous acid solution having a constant concentration cannot be produced. There was a case. Therefore, when the electrolysis is carried out by adjusting the pH of the second softened treated water, which is the water to be treated for electrolytic treatment, to 10 or more, the effective chlorine concentration can be stabilized, and hypochlorous acid is industrially produced. An acid solution can be generated.
Therefore, from the viewpoint of stabilizing the effective chlorine concentration of the hypochlorous acid solution, the pH of the water to be treated for electrolytic treatment (second softened water) is 10 or more, particularly 10.5 or more, or 12.5 or less, It is preferable to carry out the electrolysis by adjusting to 11.0 or more or 12.0 or less.

Here, as a means for adjusting the pH of the water to be treated for electrolytic treatment (second softened water) to 10 or more, a method of adjusting by adding an alkalizing agent such as NaOH can be mentioned.
In addition, the means for adjusting the pH of the water to be treated (second softened water) to 10 or more may be disposed anywhere as long as it is a previous process of the electrolytic treatment process. For example, the treated water inflow pipe 2, the first softening treatment device 3, the first softening treatment water supply tube 4, the SS removal treatment device 5, the SS removal treatment water supply tube 6, the salt removal treatment device 7, and the salt concentrated water supply tube 8 The pH adjusting means may be provided in either the second softening treatment apparatus 11 or the second softening treatment water supply pipe 12. In addition, as in the electrolytic treatment apparatus as shown in FIGS. 6 and 7, the electrolytic solution (water to be treated for electrolytic treatment) is supplied from the supply tank to the electrolytic bath, and the treatment liquid subjected to the electrolytic treatment in the electrolytic bath is supplied to the supply tank. In the electrolytic treatment apparatus configured to be returned to the circulation, the circulating treatment liquid can be adjusted to a desired pH regardless of the position of the pH adjusting unit disposed in the circulating system.

In addition, as described above, instead of performing electrolysis by adjusting the pH of the water to be treated (second softened water) to 10 or more, the pH of the electrolyzed water after electrolysis is 10 or more, Even if it is adjusted to 10.5 or more or 12.5 or less, in particular, 11.0 or more or 12.0 or less, the effective chlorine concentration can be stabilized, and a hypochlorous acid solution is produced industrially. can do.
Here, as a means for adjusting the pH of the electrolytically treated water after the electrolytic treatment to 10 or more, a method of adjusting by adding an alkalizing agent such as NaOH can be mentioned.
In addition, the means for adjusting the pH of the electrolytically treated water after electrolytic treatment to 10 or more may be placed anywhere as long as it is a subsequent step of the electrolytic treatment step. For example, the pH adjusting means may be provided at either the electrolytic cell outlet or the electrolytically treated water tank.

  In addition, the pH of the water to be treated for electrolytic treatment (second softened treated water) is adjusted to 10 or higher to conduct electrolysis, or the pH of the electrolyzed water after electrolysis is adjusted to 10 or higher. In such a case, it is preferable to store the electrolytically treated water after electrolysis so that the pH is maintained at 10 or more. By doing in this way, the effective chlorine concentration of hypochlorous acid can be stabilized also at the time of storage of electrolyzed water.

In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” or “preferably” with the meaning of “X to Y” unless otherwise specified. Also includes the meaning "is smaller than Y".
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not restrict | limited by the following Example.

<Example 1>
In this example, the leachate at the waste final disposal site was treated water.
As shown in FIG. 5, the water to be treated was introduced into the first softening treatment device 3. In the 1st softening processing apparatus 3, sodium carbonate was added to to-be-processed water, and it adjusted to pH 9.0 or more, Ca was coagulated and settled by the alkali coagulation process, and Ca density | concentration was reduced (1st softening process process). ). Next, the softened water after the first softening treatment was introduced into the SS removal treatment apparatus 5 to remove and reduce SS and organic substances in the water to be treated. In SS removal processing apparatus 5, it processed in order of biological treatment, coagulation sedimentation processing, sand filtration, activated carbon treatment, and MF membrane filtration (SS removal treatment process).
SS removal treated water obtained from the SS removal treatment apparatus 5 was introduced into the ED treatment apparatus 19 to obtain ED treatment water and ED concentrated liquid (ED treatment step). Since the ED treated water with reduced salt has a slightly high organic substance concentration, it was introduced into the RO treatment device 16 and subjected to desalination again to obtain RO treated water and RO concentrated water (RO treatment step). In the RO treated water, both the organic substance concentration and the salt concentration were sufficiently reduced. Therefore, it can be discharged out of the system as it is and reused. On the other hand, the RO concentrate was returned to the first softened water supply pipe and was repeated from the SS removal process.

  The ED concentrated liquid is introduced into the second softening treatment apparatus 11, and the ED concentrated liquid is circulated in the chelating agent adsorption tower filled with iminodiacetic acid in the second softening processing apparatus 11, and the Ca in the liquid is circulated. And Mg were removed (second softening treatment step).

The second softened water after the second softening treatment was introduced into the electrolytic treatment apparatus 13 and subjected to an electrolytic treatment to obtain electrolytic treated water that became a hypochlorous acid solution.
As shown in FIG. 6, the electrolytic treatment apparatus 13 used was configured such that the treatment liquid circulated through the electrolytic cell and the supply liquid tank. Specifically, the raw electrolytic water that is the second softened water is supplied to the supply liquid tank and temporarily stored, and the mixed liquid in the supply tank is supplied to the electrolytic bath as the liquid to be processed to perform the electrolytic treatment. The treated liquid is returned to the supply liquid tank as a circulating liquid, stirred and homogenized in the supply liquid tank, and a part of the mixed liquid in the supply tank is continuously discharged from the supply liquid tank as electrolytic treatment water. It has become.
Further, the supply liquid tank is provided with a pH meter and a pH adjusting agent charging means, that is, a device for charging a predetermined amount of NaOH according to the pH measured by the pH meter, and the pH is always 10.0 or more. Preferably, NaOH is automatically injected so as to be 11.0 to 12.0.

Table 1 shows analysis values of the water to be treated, the first softened water (“softened water”), the ED concentrated water, the second softened water, the electrolytic water, and the RO water in Example 1.
The effective chlorine concentration of the hypochlorous acid solution was measured by the iodometric titration method (the same as below).
Moreover, the calcium scale precipitation situation was judged from the analysis and the processing performance of the apparatus.

(Results and discussion)
As shown in Table 1, the water to be treated had a chromaticity of 300 degrees, a COD of 250 mg / L, a Ca concentration of 1200 mg / L, a Cl ion concentration of 8300 mg / L, and a TDS of 15000 mg / L.
In the softened water after the first softening treatment, T-Ca was reduced to 20 mg / L, and Ca could be greatly reduced. Moreover, turbidity became 50 degree | times and COD became 200 mg / L, and it fell a little from to-be-processed water. Others were the same as the treated water.
The ED concentrated water after the ED treatment had a chromaticity of 2 degrees, a COD of 2.0 mg / L, and an evaporation residue of 165000 mg / L, and was able to be concentrated about 10 times or more by the ED treatment.
In the concentrated ED concentrated water, 120 mg / L of T-Ca and 12 mg / L of T-Mg remained. Therefore, by the second softening treatment in which the chelate adsorption tower is circulated, T-Ca and T- Mg was reduced to 1.5 mg / L and 0.5 mg / L, respectively. In addition, Cl density | concentration and TDS were 81000 mg / L and 165000 mg / L, respectively, and were the same as ED concentrated water.

As a result of electrolytically treating the second softened water, a hypochlorous acid solution having an effective chlorine concentration of 2500 mg / L was obtained with the electrolytically treated water.
In the electrolytic treatment, the pH was as high as 11.0, but Ca and Mg were almost removed, so there was almost no scale formation and stable treatment performance was obtained.
On the other hand, in the RO-treated water, a good water quality was obtained with a Cl ion concentration of 120 mg / L, TDS of 250 mg / L, chromaticity of 1 degree or less, and COD of 1 mg / L or less.
From this, it was found that, in the supply liquid tank of the electrolysis apparatus, when the pH is controlled to 10.0 or higher, preferably 11.0 or higher, electrolyzed water having an effective chlorine concentration that is more stable than the electrolyzing can be obtained.
In addition, in the electrolytic treatment with a high pH, the Ca and Mg residues in the supply liquid become a scale generation factor, and therefore, these must be removed. Therefore, it was confirmed that the second softening treatment is effective.

In the second softening treatment, when the Ca and Mg concentrations of the ED concentrated water are as high as 100 mg / L or more, it has been found preferable because the softening treatment by alkali precipitation + filtration treatment is relatively low cost. On the other hand, it was found that when the ED concentrated water Ca, Mg concentration is relatively low at 100 mg / L or less, the chelate adsorption treatment can be made compact, and both Ca and Mg can be removed at a low concentration.
If the Ca concentration of the second softened water is 10 mg / L or less and the Mg concentration is 5 mg / L or less, scale generation can be suppressed in the electrolytic treatment apparatus, and both the Ca and Mg concentrations are 1 mg / L or less. As a result, it was found that more stable electrolytic treatment can be performed.

<Example 2>
In this example, the leachate from the waste landfill was treated water.
As shown in FIG. 3, leachate as the water to be treated was introduced into the first softening treatment device 3. In the 1st softening processing apparatus 3, sodium carbonate was added to to-be-processed water, and it adjusted to pH9.0 or more, and Ca density | concentration was reduced by alkali coagulation precipitation (1st softening processing process). Next, the softened water after the first softening treatment was introduced into the SS removal treatment apparatus 5 to remove and reduce SS and organic substances in the water to be treated. In SS removal processing apparatus 5, it processed in order of biological treatment, coagulation sedimentation processing, sand filtration, activated carbon treatment, and MF membrane filtration (SS removal treatment process).
The SS removal treated water obtained from the SS removal treatment device 5 was introduced into the RO treatment device 16 to perform desalting treatment, and RO treated water and RO concentrated water were obtained (RO treatment step). RO treated water, in which both organic substances and salts were greatly reduced, was discharged out of the system as final treated water. On the other hand, the RO concentrated water in which the salts were concentrated was supplied to the ED processing device 19 and subjected to ED processing to obtain an ED concentrated liquid and ED processed water (ED processing step). Although the ED treated water was reduced in salt, the organic matter concentration was high, so it was returned to the RO treatment device 1 to remove the organic matter by the RO treatment.

On the other hand, the ED concentrated liquid is introduced into the second softening treatment apparatus 11, and the ED concentrated liquid is circulated in the chelating agent adsorption tower filled with iminodiacetic acid in the second softening processing apparatus 11, and the Ca in the liquid is circulated. And Mg were removed (second softening treatment step).
The second softened water after the second softening treatment was introduced into the same electrolytic treatment apparatus 13 as in Example 1 (see FIG. 2) and subjected to an electrolytic treatment to obtain electrolytic treated water that became a hypochlorous acid solution. .

Table 2 shows analysis values of water to be treated, first softened water ("softened water"), ED concentrated water, second softened water, electrolytically treated water, and RO treated water in Example 2 above.
The effective chlorine concentration of the hypochlorous acid solution was measured by the iodometric titration method (the same as below).
Moreover, the calcium scale precipitation situation was judged from the analysis and the processing performance of the apparatus.

As shown in Table 2, the water to be treated had a chromaticity of 250 degrees, a COD of 250 mg / L, a Ca concentration of 1200 mg / L, a Cl ion concentration of 5800 mg / L, and a TDS of 10,000 mg / L. When it became the softened water after the first softening treatment, T-Ca was reduced to 20 mg / L. The first softened water with reduced Ca is subjected to the RO treatment after the SS removal treatment process, and the Cl ion concentration of the RO treated water is 120 mg / L, TDS 250 mg / L, chromaticity is 1 degree or less, and COD is 1 mg / L or less. The water quality was good.
On the other hand, as a result of performing ED treatment using RO concentrated water, ED concentrated water has a chromaticity of 2 degrees, COD of 2.0 mg / L, and evaporation residue of 165000 mg / L, which is about 16 times that of water to be treated. Double concentration was possible. However, the ED concentrated water after concentration remained T-Ca 120 mg / L and T-Mg 12 mg / L. Then, the 2nd softening process by a chelate adsorption tower was performed, and T-Ca and T-Mg of the treated water could be reduced to 1.5 mg / L and 0.5 mg / L, respectively. In addition, Cl density | concentration and TDS were 81000 mg / L and 165000 mg / L, respectively, and were the same as ED concentrated water.
As a result of further electrolytic treatment of the second softened water, a hypochlorous acid solution having an effective chlorine concentration of 2500 mg / L was obtained with the electrolytically treated water. In this electrolytic treatment, the pH was as high as 11, but Ca and Mg were almost removed, so there was almost no scale formation, and stable treatment performance was obtained.

<Reference Example 1: Electrolysis pH less than 10>
The water to be treated similar to that in Example 1 was treated with the same processing flow as in Example 1. The difference from Example 1 is the set pH of the electrolytic treatment apparatus supply tank. In Example 1, the pH was set to 11.0 or higher, while in Reference Example 1, the pH was set to 9.5.

FIG. 9 is a graph showing the effective chlorine concentration course of the produced electrolytically treated water accompanying the electrolytic treatment of Example 1 and Reference Example 1.
As a result, in Example 1, the effective chlorine concentration of the electrolytically treated water was almost constant at 2600 mg / L in 200 hours of continuous treatment. On the other hand, in Reference Example 1 in which the electrolytic treatment pH was 9.5, the effective chlorine concentration of the electrolytic treatment water greatly decreased with the passage of treatment time, and stable treatment performance was not obtained.

<Comparative Example 1: No second softening treatment>
The treatment conditions were the same as in Example 1 except that the same water to be treated as in Example 1 was used and the second softening treatment was not performed.

(result)
FIG. 10 is a graph showing the progress of current efficiency associated with electrolytic treatment in Example 1 and Comparative Example 1.
Here, the current efficiency is the ratio of the amount of electricity that has actually contributed to the production of hypochlorous acid, which is the production target substance, in the amount of electricity used in the electrolytic treatment.

In Example 1, the current efficiency was approximately 65% in a continuous processing period of about one month, and stable processing performance was obtained. On the other hand, in Comparative Example 1, the current efficiency gradually decreased from about 65% of the start of the process in the process of about one month, and greatly decreased to 22% after 30 days of the process.
In Comparative Example 1, when the electrolysis apparatus was disassembled after 30 days, it was confirmed that a large amount of Ca-based scale was generated on the electrode surface of the anode. The decrease in current efficiency was judged to be caused by the generation of scale on the electrode surface.

(Results and discussion)
As shown in the Examples, the calcium concentration can be reduced by previously performing the first softening treatment on the water to be treated containing calcium.
Next, SS removal and organic matter reduction can be achieved by performing SS removal treatment such as biological treatment, coagulation sedimentation treatment, sand filtration, activated carbon treatment, and MF membrane filtration on the softened treated water thus reduced in calcium concentration. Is possible.
Next, a good desalination treatment can be performed by performing a treatment consisting of RO and ED alone or in combination on the treated water obtained by the SS removal treatment.
Furthermore, if the second softening treatment is performed on the concentrated solution generated from the desalting treatment to reduce calcium and magnesium to a predetermined concentration or less, the concentrated solution is supplied to the electrolytic treatment apparatus and subjected to the electrolytic treatment. Thus, scale deposition derived from calcium and magnesium can be suppressed in the electrolytic treatment apparatus, and stable electrolytic treatment is possible. Furthermore, if the pH of the electrolytic treatment is 10 or more, the effective chlorine concentration of sodium hypochlorite is stabilized in the electrolytically treated water, so that the produced electrolytically treated water is used as a hypochlorous acid solution to disinfect sewage treated water or the like. Can be used. This not only facilitates effective use of salts, but also significantly reduces running costs, as compared with conventional desalted and concentrated liquid treatment using evaporative drying treatment.

<Example 3>
Example 3 was performed with the same processing flow as Example 1 shown in FIG. In addition, as shown in FIG. 7, the electrolytic processing apparatus 13 used what was comprised so that the electrolytic raw water supply to an electrolytic cell might be performed by one pass unlike Example 1. FIG. Specifically, the electrolytic raw water, which is the second softened treated water, is directly supplied to the electrolytic bath as it is to perform electrolytic treatment, and the electrolytically treated electrolytic treated water is fed to the electrolytic treated water tank.
In addition, a pH meter is installed in the electrolytically treated water tank, and a device for charging a predetermined amount of NaOH according to the pH measured by the pH meter is installed in the electrolytic cell outlet pipe, that is, a pH measured by the pH meter. NaOH is automatically injected so that the pH is always 10.0 or more, preferably 11.0 to 12.0. Furthermore, in order to make the liquid in the electrolytic treatment water tank uniform and improve the responsiveness of pH, the liquid in the electrolytic treatment water tank may be circulated in the electrolytic treatment water tank or stirred in the electrolytic treatment water tank. preferable.

(Results and discussion)
As a result of electrolytic treatment of the second softened water, a hypochlorous acid solution having an effective chlorine concentration of 2500 mg / L was obtained with the electrolytically treated water.
FIG. 11 shows the transition of the effective chlorine concentration of the hypochlorous acid solution in the electrolytically treated water tank. From this, it was confirmed that the effective chlorine concentration was stabilized when the pH was controlled to 10.0 or higher, preferably 11.0 or higher in the electrolytically treated water tank.

DESCRIPTION OF SYMBOLS 1 Organic waste water treatment apparatus 2 To-be-processed water inflow pipe 3 1st softening processing apparatus 4 1st softening processing water supply pipe 5 SS removal processing apparatus 6 SS removal processing water supply pipe 7 Salt removal processing apparatus 8 Salt concentrated water supply pipe 9 Salts Removal treatment water discharge pipe 11 Second softening treatment device 12 Second softening treatment water supply tube 13 Electrolytic treatment device 14 Sodium hypochlorite solution supply tube 15 Sodium hypochlorite solution storage tank 16 RO membrane treatment device 17 RO concentrated water Supply pipe 18 RO membrane treated water discharge pipe 19 ED treatment device 20 ED treated water supply pipe 21 ED concentrated water supply pipe

Claims (6)

From organic wastewater containing salts and organic matter, the first softening treatment step to soften and reduce the calcium concentration, biological treatment, coagulation sedimentation treatment, activated carbon adsorption treatment, sand filtration treatment, microfiltration membrane treatment And an SS removal treatment step comprising one or more treatments selected from the group consisting of or a combination of two or more,
After performing the first softening treatment step and the SS removal treatment step,
An electrodialysis treatment step for separating electrodialyzed concentrated water and electrodialyzed water by electrodialysis treatment, a reverse osmosis membrane treatment step for separating reverse osmosis concentrated water and reverse osmosis membrane treated water by reverse osmosis membrane treatment, and NF A salt removal treatment step including any step or two or more types of steps of an NF membrane treatment step that separates into NF membrane concentrated water and NF membrane treated water by membrane treatment,
The salt concentration water obtained in the salt removal step, i.e., electrodialysis concentration water, reverse osmosis concentration water or NF membrane concentration water, is subjected to a second softening treatment step of performing a softening treatment to reduce the calcium concentration, Next, an organic wastewater treatment method comprising performing an electrolytic treatment step of electrolyzing the second softened water obtained in the second softening treatment step to produce a sodium hypochlorite solution. In the first softening treatment step, the calcium concentration of the treated water is 10 mg / L to 100 mg / L,
The method for treating organic wastewater according to claim 1, wherein in the second softening treatment step, the calcium concentration of the treated water is less than 10 mg / L and the magnesium concentration is less than 5 mg / L.   3. The method for treating organic wastewater according to claim 1, wherein in the electrolytic treatment step, electrolysis is performed by adjusting the pH of the water to be treated to 10 or more.   The method for treating organic wastewater according to claim 1 or 2, wherein in the electrolytic treatment step, the pH of the electrolytically treated water after electrolysis is adjusted to 10 or more.   The organic wastewater treatment method according to claim 3 or 4, further comprising a storage step of maintaining the pH of the electrolyzed water after electrolysis obtained in the electrolyzing step at 10 or more. A first softening treatment device that softens the organic wastewater containing salts and organic matter to reduce the calcium concentration;
SS removal treatment apparatus consisting of one or more treatments or a combination of two or more selected from the group consisting of biological treatment, coagulation sedimentation treatment, activated carbon adsorption treatment, sand filtration treatment, microfiltration membrane treatment,
Electrodialysis treatment device that separates electrodialyzed concentrated water and electrodialyzed water by electrodialysis treatment, reverse osmosis membrane treatment device that separates reverse osmosis concentrated water and reverse osmosis membrane treated water by reverse osmosis membrane treatment, NF membrane treatment A salt removal device including any one of the NF membrane treatment devices or the two or more types of these devices separated into the NF membrane concentrated water and the NF membrane treated water by
A second softening device that softens the electrodialysis concentrated water, reverse osmosis concentrated water, or NF membrane concentrated water to reduce the calcium concentration;
An electrolytic treatment apparatus for electrolyzing the second softened water obtained by the second softening treatment apparatus to produce a sodium hypochlorite solution;
Organic wastewater treatment equipment with

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