JP2019042651A - Treatment device and treatment method of hardness component-containing water - Google Patents

Abstract

To provide a treatment device and a treatment method of hardness component-containing water, capable of reducing amount of a hardness component in concentrated water flowing out to a rear stage in a device and a method for conducting the reverse osmosis membrane treatment after a softening treatment of the hardness component-containing water.SOLUTION: There is provided a treatment device 1 of hardness component-containing water having a reaction tank 12 for insolubilizing a hardness component by adding at least one of an alkali agent and a carbonate compound to water to be treated containing the hardness component, a solid liquid separation device 16 for solid liquid separating the resulting insoluble article, a reverse osmosis membrane treatment device 20 for treating the solid liquid separation liquid with a reverse osmosis membrane to obtain concentrated water and permeable water, and a return pipe 38 for returning at least a part of the resulting concentrated water to a front stage of solid liquid separation means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus and method for treating water containing hardness components.

  As a method of reducing the volume of drainage, it is practiced to concentrate the drainage using a reverse osmosis membrane and recover permeated water. In recent years, the need to reduce the amount of drainage has further increased, and the concentration rate of drainage has been increased as much as possible, and factories etc. which have been performed up to ZLD (Zero Liquid Discharge) are also increasing.

  Therefore, methods have been practiced in which the concentrated water of the reverse osmosis membrane is further treated with the reverse osmosis membrane or concentrated by a method such as evaporation concentration. As described above, when the concentration factor of the drainage is high, the risk of scaling due to the hardness component and the like in the drainage increases. When scale is generated, the reverse osmosis membrane may be clogged to reduce the amount of permeated water, or the heat transfer surface of evaporative concentration may be covered by the scale to reduce the heat transfer efficiency.

  Therefore, it is desirable to reduce the hardness component in the drainage as much as possible by the softening treatment and the like before the reverse osmosis membrane treatment. As a method of softening the waste water containing the hardness component, as disclosed in Patent Document 1, there is known a method in which the hardness component in the waste water is precipitated as calcium carbonate or magnesium hydroxide to perform solid-liquid separation. When the drainage contains calcium as a hardness component, this solid-liquid separated softened water is saturated with calcium carbonate, so acid is added to increase the solubility of calcium carbonate, and decarboxylation is performed in the latter stage. Measures are taken to control the precipitation of calcium carbonate.

  In the softened water by this softening treatment, a hardness component of the dissolved amount usually remains in the range of several mg / L to several tens mg / L. Since calcium hardness components are removed as calcium carbonate, the calcium concentration of the softened water is determined by the concentration of carbonate ions remaining in the softened water, and if the carbonate ion concentration is high, the calcium hardness is lowered, but that amount of carbonic acid It requires a large amount of injection and is costly. Since the magnesium hardness component is removed as magnesium hydroxide, the magnesium concentration of the softened water changes with pH. If the pH is 11.0 or more, the magnesium hardness component can be removed to 1 mg / L or less, but if the pH is 10.5, magnesium hardness components of several mg / L to several tens mg / L remain.

  As described above, even if the hardness component in the waste water is reduced by the softening treatment before the reverse osmosis membrane treatment, the hardness component remains in the softened water, so the concentration factor in the concentration by the reverse osmosis membrane in the latter stage Higher the risk of scaling later.

  Although there is also a method of treating with an ion exchange resin to further remove the hardness component remaining in the softened treated water, the treatment cost increases.

Patent No. 5906892

  The object of the present invention is to use an apparatus and method for performing reverse osmosis membrane treatment after softening treatment of hardness component-containing water, which can reduce the amount of hardness component of concentrated water flowing out to the latter stage. Processing apparatus and processing method

  The present invention relates to a reaction vessel for adding at least one of an alkaline agent and a carbonate compound to water to be treated containing a hardness component to insolubilize the hardness component, and a solid-liquid separation for solid-liquid separation of the obtained insoluble matter Separation means, reverse osmosis membrane treatment means for obtaining concentrated water and permeated water by treating the obtained solid-liquid separated liquid with a reverse osmosis membrane, and at least a portion of the obtained concentrated water from the solid-liquid separation means And a return means to be returned to the front stage of the treatment apparatus for water containing hardness component.

  It is preferable that the return destination of the said concentrated water by the said return means is the said reaction tank in the processing apparatus of the said hardness component containing water.

In the hardness components contained water treatment device, it is preferable that CaCO ₃ concentration of the reaction vessel to return the concentrated water so that 100 mg / L or more.

  The apparatus for treating hardness component-containing water further comprises an ion concentration measuring means for measuring the ion concentration of the concentrated water, and adjusting the amount of the concentrated water returned by the return means according to the measured value. preferable.

  The present invention also includes an insolubilizing step of adding at least one of an alkaline agent and a carbonic acid compound to water to be treated containing a hardness component to insolubilize the hardness component, and a solid-liquid separation of the obtained insoluble matter Separation step, reverse osmosis membrane treatment step of obtaining the concentrated water and permeated water by treating the obtained solid-liquid separated liquid with a reverse osmosis membrane, and performing at least a part of the obtained concentrated water on the solid-liquid separation step And a return step of returning to the previous stage of the treatment of hardness component-containing water.

  In the method of treating hardness component-containing water, preferably, the return destination of the concentrated water in the return step is a reaction tank to which at least one of the alkali agent and the carbonic acid compound is added.

In the method of treating hardness component-containing water, it is preferable to return the concentrated water so that the concentration of CaCO ₃ in the reaction tank is 100 mg / L or more.

  In the method for treating hardness component-containing water, it is preferable to measure the ion concentration of the concentrated water and adjust the amount of the concentrated water to be returned in the return step according to the measured value.

  In the present invention, it is possible to reduce the amount of the hardness component of the concentrated water flowing out to the subsequent stage in the apparatus and method for performing the reverse osmosis membrane treatment after the softening treatment of the hardness component-containing water.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows an example of the processing apparatus of the hardness component containing water which concerns on embodiment of this invention. FIG. 2 is a schematic configuration view showing a processing apparatus used in Example 1. It is a schematic block diagram which shows the processing apparatus used by the comparative example 1. FIG. It is a graph which shows Ca concentration (mg-CaCO ₃ / L) to the reaction time (min) in Example 2. It is a graph which shows solubility (mg / L) of calcium carbonate to pH of water of 25 ° C. Is a graph showing the solubility of silica to pH of 25 ° C. of water (mgSiO ₂ / L).

  Embodiments of the present invention will be described below. The present embodiment is an example for implementing the present invention, and the present invention is not limited to the present embodiment.

  An outline of an example of a treatment apparatus for a water containing a hardness component according to an embodiment of the present invention is shown in FIG. 1, and the configuration thereof will be described.

  The treatment apparatus 1 for water containing a hardness component comprises a reaction tank 12 for adding at least one of an alkaline agent and a carbonate compound to water to be treated containing a hardness component to insolubilize the hardness component, and the obtained insoluble matter As a reverse osmosis membrane treatment means for obtaining concentrated water and permeated water by treating the resulting solid-liquid separated liquid with a reverse osmosis membrane as solid-liquid separation means for solid-liquid separation And 20. The treatment apparatus 1 for hardness component-containing water comprises a water tank 10 for storing water to be treated and a polymer for performing a coagulation reaction by adding a polymer flocculant to the reaction liquid obtained in the reaction tank 12 The reactor 14 may further include a solid-liquid separated liquid tank 18 for storing the solid-liquid separated liquid obtained in the precipitation tank 16.

  In the treatment apparatus 1 for the treatment of hardness component-containing water in FIG. 1, the outlet of the treated water tank 10 and the treated water inlet of the reaction vessel 12 are connected by a pipe 26 via a pump 22. The outlet of the reaction tank 12 and the inlet of the polymer reaction tank 14 are connected by a pipe 28. The outlet of the polymer reaction tank 14 and the inlet of the precipitation tank 16 are connected by a pipe 30. The solid-liquid separated liquid outlet of the settling tank 16 and the inlet of the solid-liquid separated liquid tank 18 are connected by a pipe 32. A sludge pipe 58 is connected to the sludge outlet of the settling tank 16. The outlet of the solid-liquid separated liquid tank 18 and the inlet of the reverse osmosis membrane treatment apparatus 20 are connected by a pipe 34 via a pump 24. A permeated water pipe 36 is connected to the permeated water outlet of the reverse osmosis membrane treatment apparatus 20. The concentrated water outlet of the reverse osmosis membrane treatment apparatus 20 and the return water inlet of the reaction tank 12 are connected via the valve 54 by the return pipe 38 as return means for returning at least a part of the obtained concentrated water to the front stage of the settling tank 16 Is connected. A concentrated water pipe 40 is connected between the concentrated water outlet in the return pipe 38 and the valve 54 via a valve 56. The reaction vessel 12 is connected with a carbonic acid compound addition pipe 42 as a carbonic acid compound addition means and an alkali agent addition pipe 44 as an alkali agent addition means, and a stirring device 50 provided with a stirring blade as a stirring means is installed. A polymer coagulant addition pipe 46 is connected to the polymer reaction tank 14 as a polymer coagulant addition means, and a stirring device 52 provided with a stirring blade as a stirring means is installed. The pipe 32 is connected with a pH adjuster addition pipe 48 as a pH adjuster addition means.

  The processing method of the hardness component-containing water and the operation of the treatment apparatus 1 for the hardness component-containing water according to the present embodiment will be described.

  The hardness component-containing water, which is water to be treated, is stored in the water tank 10 to be treated, if necessary, and is sent to the reaction tank 12 through the pipe 26 by the pump 22. In the reaction tank 12, at least one of the alkaline agent and the carbonic acid compound is added to the water containing the hardness component to insolubilize the hardness component (insolubilization step). The alkali agent is added to the reaction tank 12 through the alkali agent addition pipe 44, and the carbonic acid compound is added to the reaction tank 12 through the carbonic acid compound addition pipe 42. In the reaction tank 12, the reaction solution may be stirred by the stirring device 50.

The insolubilization reaction is represented, for example, by the following formula. The calcium hardness component, which is a temporary hardness component, is insolubilized in calcium carbonate using, for example, calcium hydroxide (Ca (OH) ₂ ) as an alkali agent. Alternatively, the calcium hardness component, which is a permanent hardness component, is insolubilized in calcium carbonate using, for example, sodium carbonate (Na ₂ CO ₃ ) as a carbonate compound. The magnesium hardness component is insolubilized in magnesium hydroxide using, for example, sodium hydroxide (NaOH) as an alkali agent.
Ca (HCO ₃ ) ₂ + Ca (OH) ₂ → 2CaCO ₃ + 2H ₂ O
CaCl ₂ + Na ₂ CO ₃ → CaCO ₃ + 2 NaCl
MgCl ₂ + 2 NaOH → Mg (OH) ₂ + 2 NaCl

  The reaction liquid obtained in the insolubilization step is sent from the reaction vessel 12 to the polymer reaction vessel 14 through the pipe 28. In the polymer reaction tank 14, a polymer flocculant is added to the reaction liquid through the polymer flocculant addition pipe 46 as needed to carry out a coagulation reaction (aggregation step). The coagulated liquid may be stirred by the stirring device 52 in the polymer reaction tank 14.

  The coagulated liquid obtained in the aggregation step is sent from the polymer reaction tank 14 to the precipitation tank 16 through the pipe 30. In the precipitation tank 16, the obtained insoluble matter is subjected to solid-liquid separation by natural sedimentation or the like (solid-liquid separation step).

  The solid-liquid separated liquid obtained in the solid-liquid separation step is sent from the settling tank 16 through the pipe 32 to the solid-liquid separated liquid tank 18 as needed, and stored. In the pipe 32, if necessary, a pH adjuster may be added to the solid-liquid separated solution through the pH adjuster addition pipe 48 to adjust the pH of the solid-liquid separated solution (pH adjustment step). pH adjustment may be performed in the solid-liquid separated liquid tank 18. On the other hand, the sludge obtained in the solid-liquid separation step is discharged through the sludge pipe 58.

  The solid-liquid separated liquid is fed by the pump 24 through the pipe 34 to the reverse osmosis membrane treatment apparatus 20. In the reverse osmosis membrane treatment apparatus 20, the solid-liquid separated liquid is treated with the reverse osmosis membrane to obtain concentrated water and permeated water (reverse osmosis membrane treatment step). The permeated water obtained in the reverse osmosis membrane treatment step is discharged through the permeated water pipe 36, and is recovered and reused or discarded. At least a portion of the concentrated water obtained in the reverse osmosis membrane treatment step is returned to the reaction tank 12 which is the front stage of the precipitation tank 16 (solid-liquid separation step) through the return pipe 38 (return step). At least a portion of the concentrated water may be returned to the solid-liquid separated liquid tank 18.

  Thus, in the method and apparatus for treating hardness component-containing water according to the present embodiment, solid-liquid separation including the hardness component after the softening treatment (insolubilization step, aggregation step, solid-liquid separation step) of the hardness component-containing water The solution is concentrated by reverse osmosis membrane treatment, and at least a portion of the concentrated water is returned to the previous stage of the solid-liquid separation step.

  Thereby, the amount of the hardness component of the concentrated water which flows out to the latter stage can be reduced. Even if concentration treatment such as reverse osmosis membrane treatment or evaporation concentration treatment is performed at the latter stage of reverse osmosis membrane treatment, the equipment can be miniaturized. In addition, precipitation of the hardness component is suppressed in concentration processing such as reverse osmosis membrane treatment and evaporation concentration treatment at the latter stage of reverse osmosis membrane treatment, and the system can be stably operated.

  The return destination of the concentrated water by the return means may be a stage before the settling tank 16 (solid-liquid separation step), and is not particularly limited. For example, at least a portion of the concentrated water may be returned to at least one of the treated water tank 10, the reaction tank 12, the polymer reaction tank 14, and the pipes 26, 28, 30; It is more preferable that the hardness component in the concentrated water can promote precipitation of calcium carbonate and magnesium hydroxide in the reaction tank 12 by being returned to the reaction tank 12 to which at least one is added. For example, since the precipitation reaction of calcium carbonate proceeds by the precipitation of calcium carbonate on the surface of the formed crystals, the reaction time is higher when calcium carbonate particles are present or when the concentration of the calcium hardness component is high. Is considered to be short.

In this case, it is preferable to return the concentrated water so that the concentration of calcium carbonate (CaCO ₃ ) in the reaction tank 12 is 100 mg / L or more, and more preferable to return the concentrated water so as to be 1000 mg / L or more . When the concentration of calcium carbonate (CaCO ₃ ) in the reaction tank 12 is less than 100 mg / L, precipitation of calcium carbonate in the reaction tank 12 may be difficult to be promoted.

  The amount of concentrated water returned to the front stage of the sedimentation tank 16 (solid-liquid separation step) can reduce the load of hardness flowing out to the rear stage of the reverse osmosis membrane treatment, but the hardness component-containing water which is the water to be treated These components may be concentrated in the system if they contain ionic components that are difficult to remove by coagulation precipitation such as sodium chloride (NaCl). If the concentration factor is too high, the osmotic pressure will be high and the operation pressure in the reverse osmosis membrane will be high, so it is desirable to send a predetermined amount of concentrated water to the latter stage of the reverse osmosis membrane treatment. In order to adjust the amount of liquid sent to the latter stage of reverse osmosis membrane treatment, it further comprises, for example, an ion concentration measuring means for measuring the ion concentration of concentrated water, and the amount of concentrated water returned by the return means according to the measured value. It is preferable to adjust the For example, there is a method of measuring the conductivity in the concentrated water and adjusting the amount of liquid concentrate to be fed to the latter stage of the reverse osmosis membrane treatment so that the conductivity is less than or equal to a predetermined value. The adjustment of the flow rate of concentrated water is performed, for example, by adjusting the opening degree of the valves 54 and 56.

  When measuring the conductivity of the concentrated water and adjusting the amount of pumped concentrated water, it is desirable that the osmotic pressure does not exceed the upper pressure limit in reverse osmosis membrane treatment, and the value should be 30000 μS / cm or less Preferably, it is more preferably 20000 μS / cm or less. If the conductivity of the concentrated water exceeds 30,000 μS / cm, the osmotic pressure of the reverse osmosis membrane may be high, and the pressure limit of the reverse osmosis membrane may be exceeded.

  In the latter stage of reverse osmosis membrane treatment, as means for further concentrating concentrated water, reverse osmosis membrane treatment, heating evaporation and concentration treatment, forward osmosis membrane treatment, electrodialysis treatment and the like can be mentioned, but from the point of suppressing treatment cost low. Reverse osmosis membrane treatment is preferred. According to the method and apparatus for treating hardness component-containing water according to the present embodiment, stable treatment can be performed even when the subsequent stage of reverse osmosis membrane treatment is further reverse osmosis membrane treatment.

The hardness component-containing water to be treated is, for example, underground water, industrial water, industrial waste water, and the like. The amount of the calcium hardness component in the water containing the hardness component is, for example, 50 to 5000 mg-CaCO ₃ / L, and the amount of the magnesium hardness component is, for example, 10 to 1000 mg-CaCO ₃ / L. When the hardness component-containing water contains silica, the amount of silica in the hardness component-containing water is, for example, 10 to 400 mg / L.

Examples of the alkali agent used in the insolubilization step include calcium hydroxide (Ca (OH) ₂ ), sodium hydroxide (NaOH), potassium hydroxide (KOH) and the like. Among these, calcium hydroxide and sodium hydroxide are preferable in terms of chemical cost and the like. The carbonic compound used in the insolubilization process, for example, sodium carbonate _(Na 2 _CO 3), sodium bicarbonate (NaHCO _3), carbon dioxide, and the like. Among these, sodium carbonate is preferable in terms of drug cost and the like.

  The addition amount of the alkali agent and the carbonic acid compound in the insolubilization step is in the range of 1.0 mol to 1.2 mol with respect to the amount (1 mol) of the calcium hardness component in the water containing the hardness component to be treated water. Is preferable, and the range of 1.0 mol to 1.1 mol is more preferable. Moreover, it is preferable that it is the range of 2.0-2.4 mol with respect to the quantity (1 mol) of a magnesium hardness component, and it is more preferable that it is the range of 2.0-2.2 mol. If the addition amount of the alkali agent and the carbonic acid compound in the insolubilization step is less than the equivalent molar amount with respect to the amount (1 mol) of the hardness component in the water containing the hardness component, the insolubilization reaction may not proceed sufficiently. May be disadvantageous in terms of the cost of medicine.

  The reaction temperature in the insolubilization step is not particularly limited, and is, for example, in the range of 15 ° C to 30 ° C.

  As a polymer coagulant | flocculant used at an aggregation process, polymer coagulant | flocculants, such as an acrylamide type and an acrylic ester type, are mentioned, for example. Among these, acrylamide-based polymer flocculants are preferable in terms of drug cost and the like.

  The addition amount of the polymer coagulant in the aggregation step is preferably in the range of 0.5 to 5.0 mg / L, and more preferably in the range of 1 to 2 mg / L. If the addition amount of the polymer flocculant in the aggregation step is less than 0.5 mg / L, the aggregation reaction may not proceed sufficiently, and if it is added excessively, it may be disadvantageous in terms of drug cost and the like.

  The reaction temperature in the aggregation step is not particularly limited, and is, for example, in the range of 15 ° C to 30 ° C.

  The method of solid-liquid separation in the solid-liquid separation step is not particularly limited, and examples thereof include methods such as sand filtration and membrane filtration in addition to sedimentation by natural sedimentation. Among these, the settling tank by natural sedimentation is preferable from the point of equipment cost etc.

  As a pH adjuster used at a pH adjustment process, acids, such as hydrochloric acid and a sulfuric acid, or alkali agents, such as sodium hydroxide, are mentioned, for example.

  In the pH adjustment step, the pH is preferably adjusted to a range of 4 to 10, and more preferably adjusted to a range of pH 5 to 8. If the pH is less than 4, the cost of the acid may be excessive. If the pH is more than 10, the scale inhibition effect of calcium carbonate may be insufficient.

  The hardness component is difficult to precipitate because it has high solubility in the acidic region (see FIG. 5), but when the water containing hardness component contains a silica component, the silica component tends to precipitate because it has low solubility in the acidic region (see FIG. 6) Therefore, the hardness component may be insolubilized and removed (solid-liquid separation) by the above-mentioned method, and it may be treated, for example, at pH 9.5 or more in the reverse osmosis membrane treatment step.

  When the hardness component-containing water contains a silica component, another reaction tank (second reaction tank) is provided in the reaction tank 12 or at the front stage or rear stage of the reaction tank 12 and a magnesium compound is added to insolubilize the silica, You may remove by the said solid-liquid separation process. In this case, reverse osmosis membrane treatment can be performed at any pH.

The magnesium compound used for the insolubilization of the silica component, for example, magnesium hydroxide (Mg _(OH) 2), magnesium chloride (MgCl _2), inorganic salts such as magnesium such as magnesium oxide (MgO) and the like. Among these, magnesium hydroxide is preferable in terms of chemical cost and the like.

  The amount of the magnesium compound added is preferably in the range of 0.5 mol to 5.0 mol, and more preferably in the range of 1.0 mol to 2.5 mol with respect to the amount (1 mol) of silica in the water to be treated. It is more preferable that If the addition amount of the magnesium compound is less than 0.5 mol with respect to the amount (1 mol) of silica in the water to be treated, the insolubilization reaction may not proceed sufficiently, and if it exceeds 5.0 mol, the drug cost It may be disadvantageous in terms of etc.

  The reverse osmosis membrane used in the reverse osmosis membrane treatment is not particularly limited, and is, for example, a polyimide-based reverse osmosis membrane.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples, but the present invention is not limited to the following examples.

Example 1 and Comparative Example 1
The water flow test was performed in the experimental equipment of the flow shown in FIG. 2 (Example 1) and FIG. 3 (Comparative Example 1). In Example 1, part of the concentrated water was returned to the reaction tank.

(Water to be treated)
Water to be treated: Factory effluent (containing hardness component)
Ca = 200 mg-CaCO ₃ / L, Mg = 50 mg-CaCO ₃ / L
HCO ₃ ⁻ = 200 mg-CaCO ₃ / L

In Example 1, water flowed into the reaction tank at a treated water flow rate of 140 L / h. In a reaction tank, calcium hydroxide (Ca (OH) ₂ ) is added as an alkali agent to adjust to pH 10.8 to 11.0, and 100 mg-CaCO ₃ / L of sodium carbonate (Na ₂ CO ₃ ) as a carbonate compound. Added. In a polymer reaction tank, 2 mg / L of Orfloc M-4020 (manufactured by Organo Corporation) was added as a polymer coagulant. Solid-liquid separation was performed by a sedimentation tank as a solid-liquid separation device. The solid-liquid separated liquid was passed through the solid-liquid separated liquid tank at a flow rate of 200 L / h. The solid-liquid separated liquid was passed through a 4-inch RO element (manufactured by Nitto Denko, LFC-3) as a reverse osmosis membrane treatment device at a flow rate of 720 L / h. The permeated water is obtained by reverse osmosis membrane treatment at a flow rate of 120 L / h, the concentrated water is circulated to the solid-liquid separated liquid tank at a flow rate of 520 L / h, returned to the reaction tank at a flow rate of 60 L / h, and the latter stage at a flow rate of 20 L / h. The solution was sent to the concentrator of In Example 1, the concentrated water was returned so that the CaCO ₃ concentration in the reaction tank was 155 mg / L. The results are shown in Table 1.

In the comparative example 1, it flowed into the reaction tank by the to-be-processed water flow volume of 140 L / h. In a reaction tank, calcium hydroxide (Ca (OH) ₂ ) is added as an alkali agent to adjust to pH 10.8 to 11.0, and 100 mg-CaCO ₃ / L of sodium carbonate (Na ₂ CO ₃ ) as a carbonate compound. Added. In a polymer reaction tank, 2 mg / L of Orfloc M-4020 (manufactured by Organo Corporation) was added as a polymer coagulant. Solid-liquid separation was performed by a sedimentation tank as a solid-liquid separation device. The solid-liquid separated liquid was passed through the solid-liquid separated liquid tank at a flow rate of 140 L / h. The solid-liquid separated solution was passed through a 4-inch RO element (manufactured by Nitto Denko, LFC-3) as a reverse osmosis membrane treatment device at a flow rate of 684 L / h. Permeated water was obtained at a flow rate of 84 L / h by reverse osmosis membrane treatment, concentrated water was circulated to the solid-liquid separated liquid tank at a flow rate of 544 L / h, and was sent to the downstream concentrator at a flow rate of 56 L / h. The results are shown in Table 2.

The amount of Ca and Mg in water is measured using an ion chromatograph (IC 761 manufactured by Metrome), and the amount of HCO ₃ ⁻ is inorganic using a TOC meter (TOC-3000 manufactured by Shimadzu Science) The value of carbon was measured and converted.

  In Example 1, the Ca load and the Mg load of RO concentrated water are reduced by returning a part of the concentrated water to the reaction tank that is the front stage of the precipitation tank (solid-liquid separation tank), and the reverse osmosis membrane treatment device The amount of hardness component flowing out to the later stage decreased. On the other hand, in Comparative Example 1, since concentrated water was not circulated, there were many hardness components which flowed out to the latter stage of the reverse osmosis membrane treatment apparatus.

Example 2
The return destination of the concentrated water was examined. Deposition reaction CaCO _3, in order to proceed by the CaCO ₃ in the generated surface of the crystals precipitated, and if the pre-particles of CaCO ₃ are present, who when the concentration of Ca is high, short reaction time It is thought that it is finished.

[Jar test procedure]
The raw water _{(Ca = 250mg-CaCO 3 /} L), and the CaCO ₃ content sludge by adding 0,100,1000,10000mg / L. Thereto, 417 mg of Na ₂ CO ₃ / CaCO ₃ / L was added, and adjusted to pH 11 with sodium hydroxide (NaOH). The reaction was performed at 120 rpm with a jar tester. After filtering with a 0.45 μm filter, the Ca concentration of the treated water was measured.

FIG. 4 shows the result of the jar test. The graph of FIG. 4 shows the Ca concentration (mg-CaCO ₃ / L) with respect to the reaction time (min).

As described above, it was found that the precipitation of CaCO ₃ can be promoted by returning the concentrated water containing CaCO ₃ to the reaction tank so as to be 100 mg / L or more as CaCO ₃ .

  As described above, according to the embodiment, in the apparatus and method for performing reverse osmosis membrane treatment after the softening treatment of the hardness component-containing water, the amount of the hardness component of the concentrated water flowing out to the subsequent stage can be reduced.

  1 Water hardness component-containing water treatment apparatus, 10 treated water tank, 12 reaction tank, 14 polymer reaction tank, 16 solid-liquid separation tank, 18 solid-liquid separation liquid tank, 20 reverse osmosis membrane treatment apparatus, 22, 24 pump, 26 , 28, 30, 32, 34 piping, 36 permeated water piping, 38 return piping, 40 concentrated water piping, 42 carbonated compound added piping, 44 alkali agent added piping, 46 polymer coagulant added piping, 48 pH adjuster added piping , 50, 52 stirrers, 54, 56 valves, 58 sludge piping.

Claims (8)

A reaction vessel for adding at least one of an alkaline agent and a carbonic acid compound to water to be treated containing a hardness component to insolubilize the hardness component;
Solid-liquid separation means for solid-liquid separation of the obtained insoluble matter;
Reverse osmosis membrane treatment means for obtaining concentrated water and permeated water by treating the obtained solid-liquid separated liquid with a reverse osmosis membrane;
Returning means for returning at least a part of the obtained concentrated water to the front stage of the solid-liquid separation means;
An apparatus for treating hardness component-containing water, comprising: The treatment apparatus for water containing hardness component according to claim 1, wherein
The apparatus for treating hardness component-containing water, wherein the return destination of the concentrated water by the return means is the reaction tank. The treatment apparatus for water containing hardness component according to claim 2, wherein
The apparatus for treating hardness component-containing water, wherein the concentrated water is returned so that the concentration of CaCO ₃ in the reaction tank is 100 mg / L or more. It is a processing apparatus of hardness component content water given in any 1 paragraph of Claims 1-3,
It further comprises an ion concentration measuring means for measuring the ion concentration of the concentrated water,
An apparatus for treating hardness component-containing water, comprising adjusting the amount of the concentrated water returned by the return means according to the measured value. An insolubilizing step of adding at least one of an alkaline agent and a carbonic acid compound to water to be treated containing a hardness component to insolubilize the hardness component;
A solid-liquid separation step of solid-liquid separation of the obtained insoluble matter;
A reverse osmosis membrane treatment step of obtaining the concentrated water and the permeated water by treating the obtained solid-liquid separated liquid with a reverse osmosis membrane;
Returning at least a part of the obtained concentrated water to a stage prior to the solid-liquid separation step;
A method of treating hardness component-containing water, comprising: It is a processing method of the hardness component content water according to claim 5,
The method for treating hardness component-containing water, wherein the return destination of the concentrated water in the return step is a reaction tank to which at least one of the alkaline agent and the carbonic acid compound is added. It is a processing method of the hardness component content water according to claim 6,
The method for treating hardness component-containing water, wherein the concentrated water is returned so that the concentration of CaCO ₃ in the reaction tank is 100 mg / L or more. It is a processing method of hardness ingredient content water given in any 1 paragraph of Claims 5-7,
A method of treating hardness component-containing water, comprising measuring the ion concentration of the concentrated water and adjusting the amount of the concentrated water to be returned in the return step according to the measured value.