JP2020018992A - Method and apparatus for treating silica/hardness component-containing water - Google Patents

Abstract

To provide a method and an apparatus for treating silica-containing water which can reduce amounts of generated regeneration waste liquid and concentrated water and can reduce treatment cost in reverse osmosis membrane treatment of the silica/hardness component-containing water.SOLUTION: A method for treating silica/hardness component-containing water includes: a softening treatment step of subjecting treated water containing silica and a hardness component by a softened resin in a softening treatment device 12; a regeneration step of regenerating the softened resin using a regenerant; a reverse osmosis membrane treatment step of passing a softened treatment water obtained by the softening treatment through a reverse osmosis membrane at at least pH 10 in a reverse osmosis membrane treatment apparatus 14 to obtain concentrated water and permeable water; and a solid-liquid separation treatment step of mixing the obtained concentrated water and a regeneration discharge liquid obtained in the regeneration step in a reaction tank 16, and then performing solid-liquid separation treatment in a settling tank 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and apparatus for treating silica / hardness component-containing water containing silica and a hardness component.

  In recent years, the amount of wastewater discharged from factories and the like has been reduced as much as possible, and a method has been adopted in which wastewater is concentrated using a reverse osmosis membrane and the like, and permeated water is collected to reduce the volume of the wastewater. I have. The water recovery rate tends to be as high as possible.In some cases, the concentrated water of the reverse osmosis membrane is further treated with a reverse osmosis membrane or concentrated by a method such as evaporation and concentration. The number of factories and the like that carry out the process up to the ZLD (Zero Liquid Discharge) for collecting, solidifying and discharging impurities is increasing.

  As described above, when the concentration ratio in the reverse osmosis membrane device or the evaporative concentration device is increased, the risk of scaling due to silica, hardness components, and the like in the wastewater increases. When the scale is generated, the reverse osmosis membrane is blocked and the amount of permeated water is reduced, or the heat transfer surface for evaporative concentration is covered with the scale, and the heat transfer efficiency is reduced.

  Therefore, it is desirable to reduce silica and hardness components in the wastewater as much as possible before the reverse osmosis membrane treatment. As a method of treating wastewater containing silica and a hardness component, as disclosed in Patent Document 1, a method of treating water by passing through a reverse osmosis membrane under alkaline conditions after performing a softening treatment to increase the solubility of silica. is there.

  In the method of passing water through a reverse osmosis membrane under alkaline conditions after performing the softening treatment, concentrated water in which silica is concentrated is discharged, but a method of treating the concentrated water has not been studied. Further, there is no study on a method for treating a regenerated drainage of a softening resin such as an ion exchange resin used in the softening treatment. This concentrated water or regenerated effluent is usually subjected to industrial waste treatment as it is, or is introduced into an evaporative concentration device to be solidified and disposed of. FIG. 2 shows a schematic configuration of a conventional silica / hardness component-containing water treatment apparatus. For example, silica / hardness component-containing water from a water tank to be treated 100 is softened using a softening resin such as an ion exchange resin in a softening apparatus 102. After the softening treatment, the alkali is added to the softening treatment water, the reverse osmosis membrane treatment is performed in the reverse osmosis membrane treatment device 104, and the concentrated water is concentrated and solidified in the evaporative concentration device 106 for disposal. In addition, regenerating drainage is generated by regenerating the ion exchange resin with the regenerating agent from the regenerating agent tank. However, this method has a problem that the evaporation energy and the cost of industrial waste treatment are large.

JP 2002-192152 A

  An object of the present invention is to reduce the amount of regenerated wastewater or concentrated water generated in the softening treatment of silica / hardness component-containing water and the reverse osmosis membrane treatment, and to reduce the treatment cost. An object of the present invention is to provide a method and a device for treating water.

  The present invention provides a softening treatment step of softening treated water containing silica and a hardness component with a softening resin; a regeneration treatment step of regenerating the softening resin using a regenerating agent; and a softening treatment obtained by the softening treatment. A reverse osmosis membrane treatment step of passing water through a reverse osmosis membrane at a pH of 10 or more to obtain concentrated water and permeated water; and a reaction tank comprising the obtained concentrated water and the regenerated effluent obtained by the regeneration treatment. And a solid-liquid separation treatment step of performing a solid-liquid separation treatment after mixing in the silica gel.

  In the silica / hardness component-containing water treatment method, after the solid-liquid separation treatment step, an acid is added to adjust the pH to 5 or less, or an alkali is added to adjust the pH to 10 or more. (2) It is preferable that the method further includes a second reverse osmosis membrane treatment step of passing water through the reverse osmosis membrane to obtain a second concentrated water and a second permeate.

  The method for treating water containing silica / hardness component preferably further includes a returning step of returning at least a part of the second concentrated water to the reaction tank.

  In the method for treating silica / hardness component-containing water, the solid-liquid separation treatment is preferably a coagulation precipitation treatment using a strong anionic polymer coagulant.

  Further, the present invention is obtained by the softening treatment means for softening treatment water containing silica and a hardness component with a softening resin; a regeneration means for regenerating the softening resin using a regenerating agent; and the softening treatment. Reverse osmosis membrane treatment means for passing the softened water through a reverse osmosis membrane at a pH of 10 or more to obtain concentrated water and permeated water; and the obtained concentrated water and the regenerated effluent obtained by the regeneration treatment. And a solid-liquid separation means for performing a solid-liquid separation treatment after mixing in the reaction tank.

  In the silica / hardness component-containing water treatment apparatus, after the solid-liquid separation treatment means, an acid is added to adjust the pH to 5 or less, or an alkali is added to adjust the pH to 10 or more. (2) It is preferable to further include a second reverse osmosis membrane treatment means for passing the water through the reverse osmosis membrane to obtain the second concentrated water and the second permeate.

  It is preferable that the apparatus for treating silica / hardness component-containing water further includes a return means for returning at least a part of the second concentrated water to the reaction tank.

  In the treatment device for water containing silica / hardness component, the solid-liquid separation treatment is preferably a coagulation precipitation treatment using a strong anionic polymer coagulant.

  According to the present invention, in the softening treatment and the reverse osmosis membrane treatment of the silica / hardness component-containing water, the amounts of regenerated wastewater and concentrated water generated can be reduced, and the treatment cost can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows an example of the processing apparatus of the silica / hardness component containing water which concerns on embodiment of this invention. It is a schematic block diagram which shows the conventional silica / hardness component containing water treatment apparatus. FIG. 2 is a schematic configuration diagram illustrating an experimental device used in Example 1 and Comparative Example 1.

  An embodiment 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.

  FIG. 1 shows an outline of an example of a silica / hardness component-containing water treatment apparatus according to an embodiment of the present invention, and its configuration will be described.

  The treatment device 1 for silica / hardness component-containing water includes a softening treatment device 12 as a softening treatment means for softening treatment water containing silica and a hardness component with a softening resin; and a regeneration treatment for regenerating a softening resin using a regenerating agent. A regenerating agent tank 26 as a means; a reverse osmosis membrane treatment device 14 as a reverse osmosis membrane treatment means for passing the softened water obtained by the softening treatment at a pH of 10 or more through a reverse osmosis membrane to obtain concentrated water and permeated water. A sedimentation tank 20 as a solid-liquid separation means for performing a solid-liquid separation process after mixing the obtained concentrated water and the regenerated effluent obtained by the regeneration process in the reaction tank 16; The treatment device 1 for silica / hardness component-containing water includes a treated water tank 10 for storing treated water, a coagulation tank 18, a turbidity device 22, and a second reverse osmosis membrane treatment device as second reverse osmosis membrane treatment means. 24.

  In the treatment device 1 for water containing silica / hardness components in FIG. 1, the outlet of the treatment water tank 10 and the treatment water inlet of the softening treatment device 12 are connected by a pipe 34 via a pump 30. The outlet of the softening treatment water of the softening treatment device 12 and the inlet of the reverse osmosis membrane treatment device 14 are connected by a pipe 36. A permeated water outlet of the reverse osmosis membrane treatment device 14 is connected to a permeated water pipe 40, and the concentrated water outlet and the concentrated water inlet of the reaction tank 16 are connected by a concentrated water pipe 38. The outlet of the reaction tank 16 and the inlet of the coagulation tank 18 are connected by a pipe 42, and the outlet of the coagulation tank 18 and the inlet of the precipitation tank 20 are connected by a pipe 44. A pipe 62 is connected to a sludge outlet at the lower part of the sedimentation tank 20 via a pump 32, and a supernatant water outlet and an inlet of the clarifier 22 are connected by a pipe 46. The outlet of the clarifier 22 and the inlet of the second reverse osmosis membrane treatment device 24 are connected by a pipe 48. A second permeated water pipe 50 is connected to the second permeated water outlet of the second reverse osmosis membrane treatment device 24, and the second concentrated water outlet and the second concentrated water inlet of the reaction tank 16 are connected by a return pipe 52. ing. The return pipe 52 is connected to a pipe 54 branched from the return pipe 52. An alkali addition pipe 64 is connected to the pipe 36 as an alkali addition means. A magnesium compound addition pipe 66 as a magnesium compound addition means and a carbonate addition pipe 68 as a carbonate addition means are connected to the reaction tank 16. A coagulant addition pipe 70 is connected to the coagulation tank 18 as coagulant addition means. An acid / alkali addition pipe 72 is connected to the pipe 46 as an acid or alkali addition means. The outlet of the regenerating agent tank 26 and the inlet of the regenerating agent of the softening device 12 are connected by a pipe 56, and the regenerating drain outlet of the softening device 12 and the inlet of the regenerating drain tank 28 are connected by a pipe 58, The outlet of the regeneration drain tank 28 and the regeneration drain inlet of the reaction tank 16 are connected by a regeneration drain addition pipe 60. In the reaction tank 16, the coagulation tank 18, and the regenerating agent tank 26, stirring devices 74, 76, 78, which are rotation driving means such as a motor, and stirring means having stirring blades and the like, are provided, respectively.

  The operation of the method for treating silica / hardness component-containing water and the treatment apparatus 1 according to this embodiment will be described.

  The silica / hardness component-containing water as the water to be treated is stored in the water tank to be treated 10 as necessary, and then sent to the softening treatment device 12 through the pipe 34 by the pump 30. In the softening device 12, the silica / hardness component-containing water is softened by a softening resin (softening process). The softened water subjected to the softening treatment is sent to the reverse osmosis membrane treatment device 14 through the pipe 36. Here, in the pipe 36, an alkali is added through an alkali addition pipe 64, and the pH is adjusted to 10 or more (alkali addition step). The softened water to which the alkali has been added is passed through the reverse osmosis membrane at a pH of 10 or more in the reverse osmosis membrane treatment device 14 to obtain concentrated water and permeated water (reverse osmosis membrane treatment step). The permeated water (silica content is, for example, less than 1 mg / L) obtained by the reverse osmosis membrane treatment is discharged through a permeated water pipe 40, and the concentrated water is sent to the reaction tank 16 through a concentrated water pipe 38. .

  On the other hand, in the softening treatment device 12, after the softening treatment is performed for a predetermined time, the softening resin is regenerated by using a regenerating agent (regeneration step). For example, a regenerating agent such as an acid or an alkali is passed from the regenerating agent tank 26 to the softening treatment device 12 through the pipe 56, discharged through the pipe 58, and stored in the regenerating drain tank 28.

  In the reaction tank 16, while being stirred by the stirring device 74, the regenerated effluent is added to the concentrated water from the regenerated effluent tank 28 through the regenerated effluent addition pipe 60 (regeneration effluent adding step), and the concentrated water and the regenerated effluent are mixed They are mixed in the reaction tank 16. In the reaction tank 16, the silica which is alkaline and highly concentrated and the magnesium in the regenerated effluent react under alkaline conditions to insolubilize the silica (insolubilization step). When the amount of magnesium in the regenerated effluent is insufficient, a magnesium compound may be added through a magnesium compound addition pipe 66 (a magnesium compound addition step).

  The reaction solution obtained in the insolubilization step is sent to the coagulation tank 18 through the pipe 42. In the coagulation tank 18, the coagulant is added to the reaction solution through the coagulant addition pipe 70 while being stirred by the stirrer 76, and the coagulation treatment is performed. The flocculated water to which the flocculant is added is sent to the precipitation tank 20 through the pipe 44, and solid-liquid separation is performed in the precipitation tank 20 (solid-liquid separation step). The supernatant water obtained by the solid-liquid separation treatment is sent to the clarifier 22 through the pipe 46. Here, in the pipe 46, an acid or an alkali is added through the acid / alkali addition pipe 72, and is adjusted to, for example, pH 5 or less or pH 10 or more (acid / alkali addition step). The sludge obtained by the solid-liquid separation treatment is discharged through a pipe 62 by a pump 32. After the turbidity treatment is performed in the turbidity removing device 22 (a turbidity treatment step), the liquid is sent to the second reverse osmosis membrane treatment device 24 through the pipe 48. In the second reverse osmosis membrane treatment device 24, water is passed through the second reverse osmosis membrane at pH 5 or lower or pH 10 or higher to obtain second concentrated water and second permeate (second reverse osmosis membrane treatment step). The second permeated water obtained by the second reverse osmosis membrane treatment is discharged as treated water (silica content is, for example, less than 1 mg / L) through a second permeated water pipe 50, and the second concentrated water is at least one of The part may be returned to the reaction tank 16 through the return pipe 52, and a part may be discharged through the return pipe 52 and the pipe 54.

  According to this method, in the reaction tank 16, alkaline concentrated silica at a high concentration and magnesium in the regenerated effluent can be reacted under alkaline conditions, and the silica is insolubilized. Silica can be reduced by solid-liquid separation by a coprecipitation reaction between silica and magnesium. The amount of the magnesium compound to be added can be reduced as compared with a case where a magnesium compound is separately prepared and added to the concentrated water of the reverse osmosis membrane treatment to insolubilize silica and solid-liquid separation is performed.

  In the method for treating silica / hardness component-containing water and the treatment apparatus 1 according to this embodiment, after the water to be treated containing silica and the hardness component is softened, the pH is adjusted to 10 or more by adding an alkali, and the reverse osmosis membrane is used. In a method of passing water through a reverse osmosis membrane in the treatment device 14 to obtain concentrated water and permeated water, the concentrated water in which silica is concentrated and the regenerated effluent obtained in the regenerating treatment are mixed in the reaction tank 16. Then, a solid-liquid separation treatment is performed to discharge the silica out of the system as solid sludge. As a result, the amount of regenerated wastewater and silica concentrated water generated is reduced, and the processing cost can be reduced. After adding the regenerated wastewater obtained by the regenerating treatment to the concentrated water in which the silica is concentrated to precipitate the silica, compared with the case where the solid-liquid separation treatment is not performed, the amount of the concentrated water of the generated silica is, for example, It can be reduced to about 1/10 to 1/20.

When the calcium concentration in the regenerated effluent is high, the calcium component may be removed as CaCO ₃ by solid-liquid separation by adding carbonate in the reaction tank 16. For example, in the reaction tank 16, carbonate is added through the carbonate addition pipe 68 (carbonate addition step). Since the concentrated water of the reverse osmosis membrane is more alkaline than in the case where the carbonate is directly added to the water to be treated, the amount of the carbonate added can be reduced.

The silica / hardness component-containing water to be treated is, for example, groundwater, industrial water, industrial wastewater, and the like. The amount of silica in the silica / hardness component-containing water is, for example, 10 to 400 mg / L. The amount of calcium hardness component of the silica / hardness components containing water, for example, a 50~5000mg-CaCO ₃ / L, the amount of magnesium hardness components are, for example, 10~1000mg-CaCO ₃ / L.

  Examples of the softening resin used in the softening treatment include a strongly acidic or weakly acidic cation exchange resin and a chelate resin. Examples of the strongly acidic cation exchange resin include Amberex 100Na manufactured by Organo Corporation. Examples of the weakly acidic cation exchange resin include IRC-76 manufactured by Organo Corporation. Examples of the chelating resin include IRC-747 UPS manufactured by Organo Corporation. Among these, a weakly acidic cation exchange resin is preferred from the viewpoint of the exchange capacity for high salt concentration wastewater and the like.

  In the case of a strongly acidic cation exchange resin, an aqueous sodium chloride solution is usually used as a regenerant. In the case of a weakly acidic cation exchange resin or chelate resin, an acid such as hydrochloric acid is used as a regenerating agent. After regenerating with an acid, an alkali such as an aqueous sodium hydroxide solution is passed through to use as a Na type. Therefore, the regenerated effluents of the acid and the alkali are discharged. By using the regenerated effluent of the acid and alkali for pH adjustment of silica insolubilization in the reaction tank 16, the amount of chemicals used can be reduced.

  When two or more types of regenerating agents are used, two or more regenerating agent tanks 26 and regenerated drainage tanks 28 may be provided.

  The pH of the softening treatment water in the reverse osmosis membrane treatment step may be 10 or more, and is preferably pH 10 to 11 from the viewpoint of membrane durability and the like. The softened water may be passed through the reverse osmosis membrane at a pH of 10 or more in the reverse osmosis membrane treatment step. When the pH of the softened water is 10 or more, the alkali addition step may not be performed.

Examples of the alkali used in the alkali addition step include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ), and the like. Of these, sodium hydroxide is preferred from the viewpoint of chemical cost and the like.

  The addition of alkali in the alkali addition step may be performed in the pipe 36 as shown in FIG. 1, may be performed in the water tank 10 to be treated, or may be performed between the water tank 10 and the softening device 12 or An alkali addition tank may be provided between the softening apparatus 12 and the reverse osmosis membrane processing apparatus 14, and the treatment may be performed in the alkali addition tank.

  The temperature in the alkali addition step is not particularly limited, but is, for example, in a range of 15 ° C to 30 ° C.

  When the regenerated effluent is added at pH 10 or more to concentrated water (silica content is, for example, 200 to 2000 mg / L) which is alkaline and is concentrated in the reverse osmosis membrane treatment device 14 and has a high concentration of silica at pH 10 or more, Silica is insolubilized and precipitated by the magnesium compound contained in the liquid. When the amount of magnesium in the regenerated effluent is insufficient, a magnesium compound may be separately added.

Examples of the magnesium compound that may be separately added in the insolubilization step include, for example, inorganic salts of magnesium such as magnesium hydroxide (Mg (OH) ₂ ), magnesium chloride (MgCl ₂ ), and magnesium oxide (MgO). Of these, magnesium hydroxide is preferred from the viewpoint of chemical cost and the like. When a magnesium compound that is hardly soluble in water, such as magnesium hydroxide or magnesium oxide, is used, a separate dissolving tank may be provided to dissolve the magnesium compound in water or the like, and then added to the reaction tank 16.

  The addition amount of the magnesium compound in the insolubilization step is preferably an amount in which magnesium is in the range of 0.5 mol to 5.0 mol with respect to the amount of silica (1 mol) in the softening treatment water, and More preferably, the amount is in the range of from about 2.5 moles to about 2.5 moles. If the addition amount of the magnesium compound in the insolubilization step is less than 0.5 mol with respect to the amount of silica (1 mol) in the softening treatment water, the insolubilization reaction may not proceed sufficiently, and may be 5.0 mol. If the amount exceeds the above, there may be a disadvantage in terms of chemical cost and the like.

  The pH may be adjusted in the insolubilization step, and the pH in the reaction tank 16 is adjusted to 10 or more, more preferably in the range of 10 to 12, and even more preferably in the range of 10 to 11. When the pH in the reaction tank 16 is less than 10, the insolubilization of magnesium is insufficient and the removability of silica is reduced. When the pH exceeds 12, the solubility of silica is increased and the removability of silica may be reduced. .

  Examples of the pH adjuster used in the pH adjustment include acids such as hydrochloric acid and sulfuric acid, and alkali agents such as sodium hydroxide.

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

  By subjecting the solid matter on which the silica is precipitated to solid-liquid separation treatment by a method such as coagulation sedimentation, the silica can be removed as a solid matter.

  As the solid-liquid separation method in the solid-liquid separation step, methods such as coagulation sedimentation treatment and membrane filtration are used, but coagulation sedimentation treatment is preferred from the viewpoint that there is no risk of membrane blockage and the like.

  The coagulation precipitation treatment includes, for example, a precipitation step of performing solid-liquid separation by spontaneous sedimentation in a precipitation tank, and may include a coagulation step of adding a coagulant and performing a coagulation treatment in a stage preceding the precipitation step. Since the sludge containing silica has poor coagulation and sedimentation properties, it is preferable to perform coagulation treatment using a coagulant such as an inorganic coagulant or a polymer coagulant as necessary in the coagulation settling treatment. The aggregation step may include an inorganic aggregation step of performing aggregation using an inorganic aggregation agent, and a polymer aggregation step of performing aggregation using a polymer aggregation agent.

  Examples of the inorganic coagulant used in the coagulation step (inorganic coagulation step) include iron-based inorganic coagulants such as ferric chloride and ferric polysulfate, and aluminum-based inorganic coagulants such as aluminum sulfate and polyaluminum chloride (PAC). Flocculants and the like.

  The amount of the inorganic coagulant added in the coagulation step (inorganic coagulation step) is preferably in the range of 20 to 200 mg / L, and more preferably in the range of 50 to 100 mg / L. If the amount of the inorganic coagulant added in the coagulation step (inorganic coagulation step) is less than 20 mg / L, the coagulation reaction may not proceed sufficiently, and if added excessively, it may be disadvantageous in terms of chemical cost and the like. is there.

  The reaction temperature in the aggregation step (inorganic aggregation step) is not particularly limited, but is, for example, in a range of 15 ° C to 30 ° C.

  As the polymer flocculant used in the flocculation step (polymer flocculation step), for example, a strong anionic polymer flocculant such as polyacrylamide-based, 2-acryloylamino-2-methylpropanesulfonic acid (AMPS) -based, Examples include anionic polymer coagulants, nonionic polymer coagulants, cationic polymer coagulants such as methacrylates and acrylates. Among these, a strong anionic polymer flocculant is preferable from the viewpoint of good cohesiveness of silica, and a strong anionic polymer flocculant and a cationic polymer flocculant may be used in combination.

  The amount of the polymer coagulant added in the aggregation step (polymer aggregation step) is preferably in the range of 0.5 to 5 mg / L, more preferably in the range of 1 to 2 mg / L. If the amount of the polymer coagulant added in the coagulation step (polymer coagulation step) is less than 0.5 mg / L, the coagulation reaction may not proceed sufficiently, and if added excessively, it is disadvantageous in terms of chemical cost and the like. May be.

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

  The solid-liquid separation water of the solid-liquid separation treatment, for example, the supernatant water obtained by the coagulation sedimentation treatment, may be discharged if it can be discharged as it is. After performing, the water is further concentrated by reverse osmosis membrane treatment (second reverse osmosis membrane treatment) by the second reverse osmosis membrane treatment device 24 to obtain highly treated permeate (second permeate) and reduce the volume. It is preferred that the Compared to the case where the second reverse osmosis membrane treatment is not performed, the amount of the concentrated silica water generated can be further reduced to, for example, about 1/2 to 1/10. By further recovering the solid-liquid separation water in the solid-liquid separation treatment, the water recovery rate of the system can be increased.

  When performing the second reverse osmosis membrane treatment, the solid-liquid separation water such as the supernatant water obtained by the coagulation sedimentation treatment is saturated with silica (silica content is, for example, 120 mg / L). Deposition can result in blockage of the film. In order to suppress this, an acid is added before the second reverse osmosis membrane treatment to adjust the pH to 5 or less (acid / alkali addition step), thereby reducing the deposition rate of silica and suppressing the deposition of silica. In the second reverse osmosis membrane treatment. Alternatively, by adding an alkali before the second reverse osmosis membrane treatment and adjusting the pH to 10 or more (acid / alkali addition step), the solubility of silica is increased again, and the precipitation of silica is suppressed to prevent the second reverse osmosis membrane. It can be concentrated by processing. At this time, by adding an acid to the solid-liquid separation water in the solid-liquid separation treatment to lower the pH, precipitation due to the remaining calcium can be suppressed, and a high water recovery rate can be achieved as a system. .

  The acids and alkalis used in the acid / alkali addition step include those described above.

  The addition of the acid or alkali in the acid / alkali addition step may be performed in the pipe 46 as shown in FIG. 1, or an acid / alkali addition tank is provided between the precipitation tank 20 and the turbidity removing device 22. It may be performed in an alkali addition tank.

  The temperature in the acid / alkali addition step is not particularly limited, but is, for example, in the range of 15 ° C to 30 ° C.

  Examples of the turbidity removing device 22 include a membrane filtration device having an ultrafiltration membrane (UF membrane), a sand filtration device, and a safety filter.

  As the second reverse osmosis membrane used in the second reverse osmosis membrane treatment, a membrane having a high silica rejection is preferable, and a membrane having a silica rejection of 99.0% or more is preferable. A silica rejection of about 0.5% is obtained, which is more preferable.

  Further, part or all of the second concentrated water (silica content is, for example, 100 to 300 mg / L) of the second reverse osmosis membrane treatment is transferred to a step before the second reverse osmosis membrane treatment, for example, the reaction tank 16. By returning it, the amount of the second concentrated water generated in the second reverse osmosis membrane treatment can be further reduced. For example, in the case where the second concentrated water generated in the second reverse osmosis membrane treatment is subjected to the evaporative concentration treatment in the evaporative concentration device after the second reverse osmosis treatment, the load of the silica flowing into the evaporative concentration device is reduced, and the evaporation is performed. Concentration can be miniaturized or unnecessary. Compared to a case where the second concentrated water in the second reverse osmosis membrane treatment is not returned to the previous stage, the amount of the concentrated silica water generated can be further reduced to, for example, about 1/2 to 1/10.

  Further, after the solid-liquid separation water of the solid-liquid separation treatment is softened again, alkali is added to increase the solubility of silica, and water is passed through the second reverse osmosis membrane in the second reverse osmosis membrane treatment device 24. Good.

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

<Example 1>
A water flow test was performed by the following method using the experimental equipment having the flow shown in FIG.

The amount of silica (SiO ₂ ) in water was measured by a JIS K0101 molybdenum blue absorption spectrophotometer using an absorptiometer (U-2900, manufactured by Hitachi, Ltd.). The amounts of Ca and Mg in the water were measured using an ion chromatography device (manufactured by Metrohm, 761Compact).

[Step (1)]
In the treated water tank 10, an aqueous solution of sodium hydroxide is added as an alkali to the treated water to adjust the pH of the treated water to 10.7-11.0, and the softening resin (weakly acidic cation exchange resin ( Water was passed through IRC-76)) manufactured by Organo Corporation. Regeneration treatment was performed by passing hydrochloric acid and sodium hydroxide aqueous solution stored in the regenerant tanks 26a and 26b, respectively, as regenerants, through the ion-exchange resin after passing water. The regeneration treatment was performed in the order of passing hydrochloric acid, washing with pure water, and passing a sodium hydroxide aqueous solution. The regenerated effluent was stored in regenerated effluent tanks 28a and 28b, respectively.

(Experiment conditions and results of step (1))
・ Water to be treated: Factory discharge water (containing silica) SiO ₂ = 50 mg / L, Ca = 20 mg / L, Mg = 10 mg / L
・ Ion exchange resin amount: 500mL
・ Column diameter: 21.5mmφ
・ Flow rate: 83 mL / min, water flow for about 100 hours (500 L in total)
・ Hardness of softened water after passing water: Ca <0.1 mg / L, Mg <0.1 mg / L
・ Hydrochloric acid: 3.7% by weight, flow rate 16.7 mL / min, water passing for 150 min (total about 2.5 L)
・ Pure water washing: Flow rate 50 mL / min, 400 min water flow (about 20 L in total) (mixed with acid regeneration wastewater)
-Sodium hydroxide aqueous solution: 4.0 wt%, flow rate 16.7 mL / min, water passing for 120 min (total of about 3.0 L)

[Step (2)]
The softened water passed through was received in the softened water tank 80, and was passed through a 4-inch reverse osmosis membrane element (LFC-3 manufactured by Nitto Denko) in the reverse osmosis membrane treatment device 14, to obtain permeated water and concentrated water. Although not shown in FIG. 3, a part of the concentrated water was circulated in the system to concentrate the silica.

(Experiment conditions and results of step (2))
・ Treatment water flow rate: 155 L / h
-Permeate flow rate: 140 L / h
・ Concentrated water flow rate: 720 L / h (of which 705 L / h is circulated to the softening tank 80 and 15 L / h is sent to the subsequent stage)
-Reverse osmosis membrane inlet flow rate: 860 L / h (including circulating water)
・ Concentrated water pH: 10.8
-Concentrated water silica concentration: 493 mg / L
・ Amount of concentrated water obtained: about 48L

[Step (3)]
The concentrated water of the reverse osmosis membrane was stored in the concentrated water tank 82 and passed through the coagulation sedimentation device. At this time, the regeneration drainage of the ion exchange resin (acid regeneration drainage (including pure water washing drainage) + alkali regeneration drainage) was added to the reaction tank 16 together with the concentrated water of the reverse osmosis membrane.

(Experiment conditions and results of step (3))
-Inlet flow rate of the coagulation sedimentation device (reaction tank 16): 100 L / h
Addition of regenerated effluent of ion exchange resin (11.3 L / h of a mixture of acid regenerated effluent and pure water washing effluent and 1.4 L / h of alkali regenerated effluent are added to reaction tank 16)
-Add 500 mg / L of sodium carbonate as a carbonate to the reaction tank 16-Adjust the pH of the reaction tank 16 to 11 by adding the alkali regeneration wastewater to the reaction tank 16-Strong anionic (polyacrylamide-based) polymer Coagulant Orfloc OA-3H (manufactured by Organo Co., Ltd.): Addition of 2 mg / L, supernatant water after precipitation: silica = 50 mg / L, Ca = 15 mg / L, Mg = 7 mg / L

[Step (4)]
The supernatant water after precipitation by the precipitation tank 20 is stored in a supernatant water tank 84 and passed through a clarifier (safety filter) to be clarified, and then, in the second reverse osmosis membrane treatment device 24, the 4-inch reverse osmosis membrane Water was passed through an element (LFC-3 manufactured by Nitto Denko) to obtain second permeated water and second concentrated water.

(Experiment conditions and results of step (4))
-Raw water flow rate of the second reverse osmosis membrane treatment: 186 L / h
-The second permeate flow rate of the second reverse osmosis membrane treatment: 140 L / h
-The second concentrated water flow rate of the second reverse osmosis membrane treatment: 720 L / h (including 674 L / h circulating in the supernatant water tank 84 and feeding 46 L / h to the subsequent stage)
・ Second reverse osmosis membrane inlet flow rate: 860 L / h (including circulating water)
-Second concentrated silica concentration water: 200 mg / L
-The amount of the obtained second concentrated water: about 12 L

  In the first embodiment, the acid regeneration effluent of the ion exchange resin in the softening treatment device 12 is added to the reaction tank 16 to treat the acid regeneration effluent and to concentrate the concentrated water using Mg in the acid regeneration effluent. Was reduced from 493 to 50 mg / L. Further, the pH of the reaction tank 16 was adjusted to 11 by adding the alkali regeneration effluent to the reaction tank 16, but by adding the alkali regeneration effluent, the alkali (sodium hydroxide) was not newly added. , The pH could be adjusted to about 11. Therefore, compared to the following Comparative Example 1, the amount of alkali added for adjusting to pH 11 could be reduced.

  Further, in Example 1, the silica was removed by the coagulation and sedimentation treatment in the step (3), so that the silica can be further concentrated by the second reverse osmosis membrane, and the amount of discharged concentrated water can be reduced. I was able to.

  As a result, compared to Comparative Example 1, the amount of concentrated water discharged from the system was reduced from about 48 L to about 12 L, that is, about 1/4. In addition, no recycled wastewater was discarded.

<Comparative Example 1>
In Comparative Example 1, the processes (1) and (2) are performed in the same manner as in Example 1, and the regenerated effluent of the ion exchange resin in the softening treatment device 12 is not added to the reaction tank 16 in Step (3). Was processed. The silica concentration of the supernatant water after precipitation remained at 493 mg / L. In Comparative Example 1, step (4) could not be performed.

  When a magnesium chloride solution was added to the reaction tank 16 in such a manner that Mg = 100 mg / L instead of the regeneration drainage, supernatant water of silica = 50 mg / L similar to that in Example 1 was obtained. The obtained concentrated water amount was about 48 L, and the regenerated drainage amount was about 25 L. At this time, the total amount of sodium hydroxide added to adjust the pH to 11 was 395 mmol.

  As described above, according to the method and apparatus of the embodiment, in the softening treatment and the reverse osmosis treatment of the silica / hardness component-containing water, it is possible to reduce the amount of regenerated effluent and concentrated water generated, thereby reducing the treatment cost. Was.

  1 silica / hardness component-containing water treatment device, 10,100 water treatment tank, 12,102 softening treatment device, 14,104 reverse osmosis membrane treatment device, 16 reaction tank, 18 coagulation tank, 20 sedimentation tank, 22 clarifier , 24 second reverse osmosis membrane treatment device, 26, 26a, 26b, 108 regenerating agent tank, 28, 28a, 28b regenerating drain tank, 30, 32 pump, 34, 36, 42, 44, 46, 48, 54, 56, 58, 62 piping, 38 concentrated water piping, 40 permeated water piping, 50 second permeated water piping, 52 return piping, 60 regeneration drainage addition piping, 64 alkali addition piping, 66 magnesium compound addition piping, 68 carbonate addition Piping, 70 coagulant addition pipe, 72 acid / alkali addition pipe, 74, 76, 78 stirrer, 80 softening water tank, 82 concentrated water tank, 84 supernatant water tank, 106 Evaporation concentrator.

Claims (8)

A softening treatment step of softening treatment water containing silica and a hardness component with a softening resin,
A regeneration step of regenerating the softening resin using a regenerating agent,
A reverse osmosis membrane treatment step of passing the softened water obtained by the softening treatment through a reverse osmosis membrane at a pH of 10 or more to obtain concentrated water and permeated water;
After mixing the obtained concentrated water and the regenerated effluent obtained in the regenerating process in a reaction tank, a solid-liquid separating process of performing a solid-liquid separating process,
A method for treating water containing silica / hardness components, comprising: The method for treating silica / hardness component-containing water according to claim 1,
After the solid-liquid separation process, an acid is added to adjust the pH to 5 or less, or an alkali is added to adjust the pH to 10 or more, and then water is passed through the second reverse osmosis membrane to perform second concentration. A method for treating water containing silica / hardness components, further comprising a second reverse osmosis membrane treatment step for obtaining water and second permeated water. The method for treating silica / hardness component-containing water according to claim 2,
A method for treating water containing silica / hardness components, further comprising a returning step of returning at least a part of the second concentrated water to the reaction tank. A method for treating silica / hardness component-containing water according to any one of claims 1 to 3,
The method for treating water containing silica / hardness components, wherein the solid-liquid separation treatment is a coagulation precipitation treatment using a strong anionic polymer coagulant. Softening treatment means for softening the water to be treated containing silica and a hardness component with a softening resin,
A regenerating means for regenerating the softening resin using a regenerating agent,
Reverse osmosis membrane treatment means for passing the softened water obtained by the softening treatment through a reverse osmosis membrane at pH 10 or higher to obtain concentrated water and permeated water,
After mixing the obtained concentrated water and the regenerated effluent obtained in the regenerating process in a reaction tank, a solid-liquid separating means for performing a solid-liquid separating process,
An apparatus for treating water containing silica / hardness components, comprising: The silica / hardness component-containing water treatment apparatus according to claim 5,
After the solid-liquid separation treatment means, an acid is added to adjust the pH to 5 or less, or an alkali is added to adjust the pH to 10 or more, and then water is passed through the second reverse osmosis membrane to perform second concentration. An apparatus for treating water containing silica / hardness components, further comprising a second reverse osmosis membrane treatment means for obtaining water and second permeated water. The silica / hardness component-containing water treatment apparatus according to claim 6,
An apparatus for treating water containing silica / hardness components, further comprising return means for returning at least a part of the second concentrated water to the reaction tank. An apparatus for treating silica / hardness component-containing water according to any one of claims 5 to 7,
An apparatus for treating water containing silica / hardness components, wherein the solid-liquid separation treatment is a coagulation precipitation treatment using a strong anionic polymer coagulant.

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