JP2019069399A - Processor and processing method for silica-containing water - Google Patents

Abstract

To provide a processor and processing method for silica-containing water, capable of reducing use amount of a magnesium compound in silica processing of a silica-containing water.SOLUTION: The processor 1 for a silica-containing water is equipped with: a reaction tank 12 for insolubilization of silica at a pH of 10 or over by adding a magnesium compound to a silica-containing water to be processed or by using magnesium in a water to be processed; a sedimentation tank 18 as first solid-liquid separation means for solid-liquid separation of the obtained insolubilized product; a sludge regeneration tank 20 as acid addition means for adding an acid to at least a part of the sludge separated by using the sedimentation tank 18; an acid addition pipe 58; a sludge separation tank 22 as second solid-liquid separation means for solid-liquid separation of the acid-added sludge; and a solid-liquid separated water return pipe 44 as return means for returning at least a part of the second solid-liquid separated water separated by using the sludge separation tank 22 to a pre-stage of the sedimentation tank 18.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus and method for treating silica-containing water.

  In recent years, it has been carried out to reduce the amount of drainage discharged from factories etc. as much as possible, and a method of concentrating the drainage using a reverse osmosis membrane etc., recovering permeated water and reducing the volume of drainage is taken. There is. The water recovery rate tends to increase as much as possible, and 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. Factories and the like are being carried out until ZLD (Zero Liquid Discharge), which recovers, solidifies and discharges impurities.

  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 the hardness component in the waste water, silica, etc. correspondingly 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 amount of silica in the drainage as much as possible before the reverse osmosis membrane treatment. As a method of treating waste water containing silica, as described in Patent Document 1, a method of removing by adding a magnesium salt under alkaline conditions is known.

  In this method of removing silica using a magnesium compound such as a magnesium salt, the addition amount of the magnesium salt is required to be several times to ten times or more of the silica concentration, which increases the cost of chemicals and increases the amount of sludge generated. there were. Moreover, although magnesium may be originally contained in the water to be treated, it is usually the case that magnesium originally contained in the water to be treated alone is not a sufficient amount for removing silica, and in this case also magnesium is separately separately It is necessary to add a compound, and there is a similar problem that the chemical cost and the amount of sludge generation increase.

JP-A-4-367783

  An object of the present invention is to provide an apparatus and method for treating silica-containing water, which can reduce the amount of magnesium compound used in the silica treatment of silica-containing water.

  The present invention adds a magnesium compound to water to be treated containing silica, or a reaction vessel for insolubilizing silica at pH 10 or more using magnesium contained in the water to be treated, and the obtained insoluble matter A first solid-liquid separation means for solid-liquid separation, an acid addition means for adding an acid to at least a part of the sludge separated by the first solid-liquid separation means, and a second for solid-liquid separation of the sludge to which the acid is added Silica-containing water comprising: solid-liquid separation means; and return means for returning at least a portion of the second solid-liquid separated water separated by the second solid-liquid separation means to the front stage of the first solid-liquid separation means. It is a processing device.

  In the treatment apparatus for silica-containing water, it is preferable to adjust the pH of the separated sludge to a range of 4 to 9 by adding the acid.

  The apparatus for treating silica-containing water further comprises a reverse osmosis membrane treatment apparatus for obtaining permeated water and concentrated water by passing the first solid-liquid separated water through the reverse osmosis membrane at a stage subsequent to the first solid-liquid separation means. Is preferred.

  In the present invention, an insolubilizing step of adding a magnesium compound to water to be treated containing silica, or insolubilizing silica at a pH of 10 or more using magnesium contained in the water to be treated, and the obtained insoluble matter A first solid-liquid separation step of solid-liquid separation, an acid addition step of adding an acid to at least part of the sludge separated in the first solid-liquid separation step, and a second solid-liquid separation of the sludge to which the acid is added A silica-containing water comprising: a solid-liquid separation step; and a return step of returning at least a portion of the second solid-liquid separated water separated in the second solid-liquid separation step to a stage preceding the first solid-liquid separation step. It is a processing method.

  In the method for treating silica-containing water, it is preferable to adjust the pH of the separated sludge to a range of 4 to 9 by adding the acid.

  The method for treating silica-containing water further includes a reverse osmosis membrane treatment step of obtaining a permeated water and a concentrated water by passing the first solid-liquid separated water through the reverse osmosis membrane at a stage subsequent to the first solid-liquid separation step. Is preferred.

  In the present invention, the amount of magnesium compound used can be reduced in the silica treatment of silica-containing water.

It is a schematic block diagram which shows an example of the processing apparatus of the silica containing water which concerns on embodiment of this invention. It is a schematic block diagram which shows the other example of the processing apparatus of the silica containing water which concerns on embodiment of this invention. It is a graph which shows elution Mg concentration (mg / L) or SiO ₂ concentration (mg / L) to sludge regeneration pH in Example 1. FIG. Example 2 is a graph showing the Mg in Comparative Example 1 amount of (new) (mg-Mg / L) for, SiO ₂ concentration in the treated water (mg / 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.

  The outline of an example of the treatment apparatus of the silica containing water which concerns on embodiment of this invention is shown in FIG. 1, and the structure is demonstrated.

  The treatment apparatus 1 for silica-containing water is obtained by adding a magnesium compound to water to be treated containing silica, or using a reaction tank 12 for insolubilizing silica at pH 10 or more using magnesium contained in the water to be treated, Sludge as the first solid-liquid separation means for solid-liquid separation of the insolubilised material, and sludge as the acid addition means for adding an acid to at least a part of the sludge separated by the precipitation tank 18 which is the first solid-liquid separation means The second separation is performed by the regeneration tank 20, the acid addition piping 58, the sludge separation tank 22 as a second solid-liquid separation means for solid-liquid separation of the sludge to which the acid is added, and the sludge separation tank 22 as a second solid-liquid separation means A solid-liquid separated water return pipe 44 is provided as a return means for returning at least a part of the solid-liquid separated water to the front stage of the precipitation tank 18. The apparatus 1 for treating silica-containing water comprises a treated water tank 10 for storing treated water, and an aggregation tank 14 for adding an inorganic coagulant to the reaction liquid obtained in the reaction tank 12 to carry out an aggregation reaction. And a polymer reaction tank 16 for adding a polymer coagulant to carry out a polymer aggregation reaction.

  In the treatment apparatus 1 for treating silica-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 30 via a pump 24. The outlet of the reaction tank 12 and the inlet of the coagulation tank 14 are connected by a pipe 32. The outlet of the coagulation tank 14 and the inlet of the polymer reaction tank 16 are connected by a pipe 34. The outlet of the polymer reaction tank 16 and the inlet of the precipitation tank 18 are connected by a pipe 36. A treated water pipe 38 is connected to the solid-liquid separated water outlet of the settling tank 18. The sludge outlet in the lower part of the settling tank 18 and the inlet of the sludge regeneration tank 20 are connected by a sludge return pipe 40 via a pump 26. The outlet of the sludge regeneration tank 20 and the inlet of the sludge separation tank 22 are connected by a reclaimed sludge pipe 42. The solid-liquid separated water outlet of the sludge separation tank 22 and the solid-liquid separated water inlet of the reaction tank 12 are connected by a solid-liquid separated water return pipe 44. A sludge pipe 46 is connected to the lower sludge outlet of the sludge separation tank 22 via a pump 28. A magnesium compound addition pipe 48 as a magnesium compound addition means, and a pH adjuster addition pipe 50 as a pH adjuster addition means are connected to the reaction tank 12, and a stirring device 60 provided with a stirring blade as a stirring means is installed . An inorganic coagulant addition pipe 52 as an inorganic coagulant addition means and a pH adjuster addition pipe 54 as a pH control agent addition means are connected to the coagulation tank 14, and a stirring device 62 equipped with a stirring blade as a stirring means is installed ing. A polymer coagulant addition pipe 56 is connected to the polymer reaction tank 16 as a polymer coagulant addition means, and a stirring device 64 provided with a stirring blade is installed as a stirring means. In the sludge regeneration tank 20, an acid addition pipe 58 is connected as an acid addition means, and a stirring device 66 provided with a stirring blade as a stirring means is installed.

  The processing method of the silica containing water which concerns on this embodiment, and operation | movement of the processing apparatus 1 of silica containing water are demonstrated.

  The silica-containing water, which is the water to be treated, is stored in the water tank 10 to be treated, if necessary, and is sent to the reaction vessel 12 through the pipe 30 by the pump 24. The amount of magnesium compound to be added can not be specified clearly because it changes according to the target silica concentration etc. of treated water, but when the silica concentration of treated water is 10 mg / L or less as an example, it becomes as follows . For example, when the pH of the water to be treated is 10 or more and magnesium is not contained in the water to be treated, or the content of magnesium in the water to be treated is 0.5 relative to the content of silica (1 mole) If it is less than the mole, the magnesium compound is added to the silica-containing water through the magnesium compound addition pipe 48 in the reaction tank 12 to insolubilize the silica (insolubilization step). For example, when the pH of the water to be treated is less than 10 and magnesium is not contained in the water to be treated, or the content of magnesium in the water to be treated is 0.5 with respect to the content of silica (1 mol) If less than the molar amount, the magnesium compound is added to the silica-containing water through the magnesium compound addition pipe 48 in the reaction tank 12, the pH adjuster is added through the pH adjuster addition pipe 50, and the pH of the water to be treated is 10 or more And the silica is insolubilized (insolubilization step). For example, when the pH of the water to be treated is less than 10 and the content of magnesium in the water to be treated is 0.5 mol or more with respect to the content (1 mol) of silica, the silica contained in the reaction tank 12 The pH adjuster is added to water through the pH adjuster addition pipe 50 to make the pH of the water to be 10 or higher, and the silica is insolubilized (insolubilization step). For example, when the pH of the water to be treated is 10 or more and the content of magnesium in the water to be treated is 0.5 mol or more with respect to the content (1 mol) of silica, the water is directly transferred to the next aggregation tank 14 It is delivered. In the reaction tank 12, the reaction solution may be stirred by the stirring device 60.

  The reaction liquid obtained in the insolubilization step is sent from the reaction tank 12 to the coagulation tank 14 through the pipe 32. In the flocculation tank 14, an inorganic flocculant is added to the reaction liquid through the inorganic flocculant addition pipe 52 as necessary to carry out a flocculation reaction (flocculation step). In the coagulation tank 14, a pH adjuster may be added through the pH adjuster addition pipe 54 as needed. In the coagulation tank 14, the coagulated liquid may be stirred by the stirring device 62.

  The aggregation reaction liquid obtained in the aggregation step is sent from the aggregation tank 14 to the polymer reaction tank 16 through the pipe 34. In the polymer reaction tank 16, as necessary, a polymer flocculant is added to the coagulation reaction liquid through the polymer flocculant addition pipe 56 to carry out a polymer flocculation reaction (polymer flocculating step). In the polymer reaction tank 16, the aggregation reaction liquid may be stirred by the stirring device 64.

  The polymer aggregation liquid obtained in the polymer aggregation step is sent from the polymer reaction tank 16 to the precipitation tank 18 through the pipe 36. In the precipitation tank 18, the obtained insolubilized material is subjected to solid-liquid separation by natural sedimentation or the like (first solid-liquid separation step).

  The first solid-liquid separated water obtained in the first solid-liquid separation step is discharged from the settling tank 18 through the treated water pipe 38 as treated water.

  At least a part of the sludge separated by the first solid-liquid separation is sent to the sludge regeneration tank 20 through the sludge return pipe 40 by the pump 26. In the sludge regeneration tank 20, an acid is added to the sludge through the acid addition pipe 58 to regenerate the sludge (acid addition step).

  The regenerated sludge is sent to the sludge separation tank 22 through the regenerated sludge pipe 42. In the sludge separation tank 22, the insolubilized material is solid-liquid separated by natural sedimentation or the like (second solid-liquid separation step).

  The second solid-liquid separated water obtained in the second solid-liquid separation step is returned through the solid-liquid separated water return pipe 44 to the reaction tank 12 at the front stage of the precipitation tank 18 (first solid-liquid separation step) Process). The sludge separated by the second solid-liquid separation is discharged from the sludge separation tank 22 by the pump 28 through the sludge pipe 46.

  Thus, in the method and apparatus for treating silica-containing water according to this embodiment, a magnesium compound is added to the silica-containing water, or the silica is insolubilized at pH 10 or more using magnesium contained in the water to be treated, Solid-liquid separation was carried out and treated (first solid-liquid separation step), acid was added to at least a part of the separated sludge, solid-liquid separation was carried out and treated (second solid-liquid separation step), separated At least a portion of the second solid-liquid separated water is returned to the previous stage of the first solid-liquid separation step.

  According to this method, by adding an acid to the sludge, the compound of magnesium and silica contained in the sludge is dissolved, and magnesium can be eluted as ions. At this time, silica is also eluted together, but since the solubility of silica is usually low (for example, about 120 mg / L at pH 4 to 9 at 25 ° C.), the amount exceeding the solubility gels and precipitates. In general, gelation of silica takes a long time (several tens of hours), but according to this method, since silica is solidified once, gelation can be sufficiently achieved even with a reaction time of about 30 minutes. it is conceivable that.

  When the regenerated sludge regenerated in the acid addition step is returned as it is to the former stage of the first solid-liquid separation step, the ionized magnesium can be reused as a magnesium compound which is a silica removing agent, and most of the silica is gelled by itself. Because it is deposited, it is separated again in the settling tank 18 and removed as sludge. However, the silica gelled alone is redissolved little by little when it is returned to the previous stage of the first solid-liquid separation step. If the amount is small, the effect is small, and there is almost no problem if it is quickly withdrawn as sludge in the sedimentation tank 18 outside the system, but if the proportion of silica that regenerates a large amount of sludge and gels alone increases, the effect Can not be ignored. Further, for example, when the treating apparatus is temporarily stopped and the gelled silica stays in the system for a long time, re-dissolution of the silica proceeds, and a phenomenon that the silica concentration of the treated water becomes significantly high can be observed. Therefore, in the treatment method and the treatment apparatus according to the present embodiment, solid-liquid separation (second solid-liquid separation treatment) is performed on the regenerated sludge regenerated in the acid addition step, thereby separating the gelled silica into the first solid-liquid separation as much as possible. The eluted magnesium (magnesium ion) can be returned to the front stage of the first solid-liquid separation process for reuse without being returned to the front stage of the process, and the amount of magnesium compound used can be reduced. In addition, the silica concentration of the treated water can be reduced with a small amount of the magnesium compound added.

  As described above, since the magnesium ion eluted from the compound of magnesium and silica contained in the sludge can be reused as the magnesium compound which is a silica removing agent, the amount of the magnesium compound used is significantly reduced as compared to the case where it is not reused. can do. Thereby, the amount of generated sludge can be reduced. In some cases, even with magnesium originally contained in the water to be treated, this magnesium can be used to insolubilize the silica to remove the silica. When the concentration of magnesium is higher than the concentration of silica in the water to be treated, removal of the silica is possible without newly adding a magnesium compound. In addition, by reusing the eluted magnesium ion, if the same magnesium compound as that in the case of not using it is used, the content of silica in treated water can be further reduced, and the treated water quality is further improved. be able to. Therefore, when a processing apparatus such as a reverse osmosis membrane processing apparatus is further provided downstream of the first solid-liquid separator, the load can be reduced.

  In the sludge regeneration step, it is preferable to add an acid to adjust the pH of the separated sludge to a range of 4 to 9. The amount of magnesium that can be regenerated is determined by the amount of acid added to the sludge regeneration tank 20, and the more it is put, the larger the amount of magnesium to be regenerated. Since the solubility of silica is in the range of pH 4 to 9 and about 120 mg / L to 150 mg / L at 25 ° C., it is considered that the silica exceeding the solubility gels and precipitates.

  If the pH is 9 or less in the sludge regeneration process, magnesium ions are eluted. Even if the pH is less than 4, although magnesium ions are eluted, the dissolved silica is less likely to gel, so the preferred pH range is pH 4 to 9, more preferably 4 to 6.

  As an acid used for regeneration of sludge, hydrochloric acid, a sulfuric acid, etc. are mentioned, for example. Among these, hydrochloric acid is preferable in terms of chemical cost and the like.

  The reaction temperature in the sludge regeneration step is not particularly limited, and is, for example, in the range of 15 ° C to 30 ° C. The reaction time in the sludge regeneration step is not particularly limited, and is, for example, in the range of 15 minutes to 120 minutes.

  The circulation amount of the second solid-liquid separated water to be returned to the previous stage of the first solid-liquid separation step may be sufficient if the amount of magnesium necessary for regeneration is sufficiently circulated, but preferably 2 to 2 of the flow rate of the water to be treated It is in the range of about 20%, more preferably in the range of about 5 to 10%. If the circulation amount of the second solid-liquid separated water is less than 2% of the flow rate of the water to be treated, the amount of magnesium necessary for regeneration may not be sufficiently supplied, and if it exceeds 20%, the flow rate of the water to be treated As a result, the reaction time in each reaction vessel may be shortened, and the processability of the silica may be deteriorated or the cohesion may be deteriorated.

  As the concentration of the returned sludge to be sent to the sludge regeneration tank 20 increases, the concentration in the sludge regeneration tank 20 increases, the ratio of silica gelling to the amount of eluted magnesium ions increases, and the regeneration efficiency improves. The concentration of the returned sludge is, for example, in the range of 0.5 to 5.0%, and preferably in the range of 1.0 to 3.0%.

  In order to increase the sludge concentration and to improve the solid-liquid separation of the regenerated sludge, at least one of the above aggregation step using an inorganic coagulant and the above-mentioned polymer aggregation step using a polymer coagulant Preferably one is done.

  The return destination of the second solid-liquid separated water by the return means may be a stage before the precipitation tank 18 (first solid-liquid separation step), and is not particularly limited. For example, the recycled sludge may be returned to at least one of the treated water tank 10, the reaction tank 12, the aggregation tank 14, the polymer reaction tank 16, and the pipes 30, 32, 34, and 36. By doing this, the magnesium ion concentration in the reaction tank 12 can be increased, and coprecipitation reaction between magnesium and silica can be promoted, which is more preferable.

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

The magnesium compound used in the insolubilization process, 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. When using a magnesium compound which is difficult to dissolve in water or the like such as magnesium hydroxide or magnesium oxide, a dissolution tank is separately provided to dissolve the magnesium compound in water or the like, and then added to the reaction tank 12 or the sludge regeneration tank 20 It is preferable to add to the sludge regeneration tank 20 in order to dissolve the magnesium compound more.

  The addition amount of the magnesium compound in the insolubilization step is such that the amount of magnesium is in the range of 0.5 mol to 5.0 mol with respect to the amount (1 mol) of silica in the silica-containing water which is the water to be treated The amount is preferably in the range of 1.0 mol to 2.5 mol, more preferably. When the addition amount of the magnesium compound in the insolubilization step is less than 0.5 mol with respect to the amount (1 mol) of silica in the silica-containing water, the insolubilization reaction may not proceed sufficiently, and it is 5.0 mol If the amount is more than the above, it may be disadvantageous in terms of drug cost and the like.

  When pH adjustment is performed in the insolubilization step, it is more preferable to adjust the pH in the reaction tank 12 to 10 or more and to adjust to a range of 10 to 12, and it is more preferable to adjust to a range of 10 to 11. When the pH in the reaction tank 12 is less than 10, the insolubilization of magnesium is insufficient and the removability of the silica decreases, and when it exceeds 12, the solubility of the silica may increase and the removability of the silica may decrease. .

  Examples of pH adjusters used for pH adjustment include acids such as hydrochloric acid and sulfuric acid, and alkali agents such as sodium hydroxide.

  When the silica-containing water contains a hardness 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 at least one of the alkali agent and the carbonate compound is added Then, the hardness component may be insolubilized and removed by the above solid-liquid separation step. The hardness component may be removed by an ion exchange resin or the like at the front stage of the reaction tank 12.

As an alkali agent used for insolubilization of a hardness component, calcium hydroxide (Ca (OH) ₂ ), sodium hydroxide (NaOH), potassium hydroxide (KOH) etc. are mentioned, for example. Among these, calcium hydroxide and sodium hydroxide are preferable in terms of chemical cost and the like. The carbonic compound used for insolubilization of hardness components, e.g., 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 is preferably in the range of 1.0 mol to 1.2 mol, preferably 1.0 mol to 1. mol, with respect to the amount (1 mol) of the hardness component in the water to be treated. More preferably, it is in the range of 1 mole. If the addition amount of the alkali agent and the carbonate compound is less than 1.0 mol with respect to the amount (1 mol) of the hardness component in the water to be treated, the insolubilization reaction may not sufficiently proceed, and when it is added excessively, It may be disadvantageous in terms of cost etc.

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

  Examples of the inorganic coagulant used in the aggregation step include iron-based inorganic coagulants such as ferric chloride and polyferric sulfate, and aluminum-based inorganic coagulants such as aluminum sulfate and polyaluminum chloride (PAC). Be

  The amount of the inorganic flocculant added in the aggregation step is preferably in the range of 30 to 300 mg / L, and more preferably in the range of 50 to 100 mg / L. If the addition amount of the inorganic coagulant in the aggregation step is less than 30 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.

  As a polymer coagulant | flocculant used at a polymer 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 flocculant in the polymer 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 coagulant in the polymer 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 etc. is there.

  The reaction temperature in the polymer 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 first solid-liquid separation step and the second solid-liquid separation step is not particularly limited, and examples thereof include methods such as sand filtration, membrane filtration, and cyclone other than sedimentation by natural sedimentation. . Among these, the settling tank by natural sedimentation is preferable from the point of equipment cost etc.

  Compared to the case where the second solid-liquid separated water is not returned to the previous stage of the first solid-liquid separation step, the amount of magnesium compound used is, for example, 1/2 to 6 by the method and apparatus for treating silica-containing water according to the present embodiment. It can be reduced to about zero. In addition, the silica content in the treated water can be reduced to, for example, about 10 mg / L or less.

  In the method and apparatus for treating silica-containing water according to the present embodiment, as shown in FIG. 2, the first solid-liquid separated treated water (treated water) is disposed downstream of the settling tank 18 (first solid-liquid separation step). It is preferable to further include a reverse osmosis membrane treatment device 68 for passing water through the reverse osmosis membrane to obtain permeated water and concentrated water, and performing the reverse osmosis membrane treatment.

  The first solid-liquid separated treated water (treated water) obtained in the sedimentation tank 18 (first solid-liquid separation step) in the treatment apparatus 3 for silica-containing water in FIG. Water to obtain permeated water and concentrated water (reverse osmosis membrane treatment step). The permeated water is discharged through the permeated water pipe 70, and the concentrated water is discharged through the concentrated water pipe 72. Since the content of silica in the first solid-liquid separated treated water (treated water) is reduced, the occurrence of scaling or the like by the silica in the reverse osmosis membrane treatment device is suppressed, and the blockage of the reverse osmosis membrane is suppressed.

  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
The effect of pH of sludge regeneration was confirmed by jar test.

(Water to be treated)
Water to be treated: RO concentrated water of pure water production line (containing silica)
SiO ₂ = 95.7 mg / L

(Sludge preparation method)
200 mg-Mg / L of magnesium chloride (MgCl ₂ ) aqueous solution as a magnesium compound was added to 50 L of water to be treated. The pH was adjusted to 11.0 by addition of sodium hydroxide (NaOH) as a pH adjuster, and reaction was allowed to proceed for 30 minutes. 2 mg / L of Orfloc M-4216 (manufactured by Organo Corporation) was added as a polymer flocculant. After standing and settling, the supernatant was discarded and concentrated to 4.4 L. The amount of Mg and SiO ₂ was measured for the supernatant. After partially dewatering the concentrated sludge by centrifugation, hydrochloric acid (HCl) was added to dissolve it, and the amounts of Mg and SiO _{2 in} the sludge were measured. The results are shown in Table 1.

The amount of Mg in the sludge in water was measured using an ion chromatography apparatus (manufactured by Metrome, 761 Compact). The amount of SiO _{2 in} the sludge in water was measured by JIS K 0101 molybdenum blue absorption photometry using an absorptiometer (manufactured by Hitachi, Ltd., U-2900).

(Sludge regeneration test)
Hydrochloric acid (HCl) as an acid was added to 100 mL of concentrated sludge to adjust each pH (pH 3 to 10) shown in Table 2 and reacted for 30 minutes. After filtration with filter paper (5C), the amounts of Mg and SiO ₂ in the filtrate were measured. The sludge is dewatered by suction filtration, dried at 105 ° C. for 2 hours, added again to 100 mL of pure water, hydrochloric acid (HCl) is added and dissolved, and the amount of Mg and SiO _{2 in} the sludge is It was measured. The results are shown in Table 2 and FIG. FIG. 3 is a graph showing the eluted Mg concentration (mg / L) or the SiO ₂ concentration (mg / L) with respect to the sludge regeneration pH.

When the pH during sludge regeneration is lowered, Mg ions are being eluted. This Mg ion can be used as a SiO ₂ remover. On the other hand, SiO ₂ has also been eluted, but in the range of pH 4 to 9, the elution amount is small and is near the solubility. The part detected above the solubility is considered to be the part not gelled due to the lack of reaction time (pH 3). In the case of pH 9, SiO ₂ is hardly eluted.

Example 2, Comparative Example 1
(Continuous water flow test)
For the confirmation, a water flow test was performed in the experimental equipment of the flow shown in FIG. In Comparative Example 1, the sludge was circulated, but no acid (hydrochloric acid) was added to the sludge regeneration tank, and the sludge separation tank was bypassed to conduct the experiment.

(Water to be treated)
Water to be treated: RO concentrated water of pure water production line (containing silica)
SiO ₂ = 100 mg / L

Water was fed to the reaction tank (17 L) at a flow rate of 100 L / h of treated water. In the reaction tank, sodium hydroxide (NaOH) was added as a pH adjuster to adjust the pH to 10.8 to 11.0, and 50 mg of magnesium chloride (MgCl ₂ ) as a magnesium compound was added. In the coagulation tank (17 L), add 100 mg / L of 35 wt% iron (III) chloride (FeCl ₃ ) aqueous solution as an inorganic flocculant, add sodium hydroxide as a pH adjuster, and adjust to pH 10.8 to 11.0. did. In a polymer reaction tank (17 L), 2 mg / L of Orfloc OA-3H (manufactured by Organo Corporation) was added as a polymer coagulant. Solid-liquid separation was performed by a settling tank as a first solid-liquid separator. The sludge after sedimentation was returned to the sludge regeneration tank (5 L) at 10% by volume (about 10 L / h) of the flow rate of the treated water, and in the sludge regeneration tank, hydrochloric acid (HCl) was added as an acid to adjust to pH5. After solid-liquid separation of the regenerated sludge after regeneration in the sludge separation tank, the supernatant liquid (second solid-liquid separated water) was returned to the reaction tank. The concentration of SiO ₂ in treated water was measured 24 hours after the start of water flow. The results are shown in FIG. FIG. 4 is a graph showing the SiO ₂ concentration (mg / L) relative to the addition amount (mg-Mg / L) of Mg (fresh) in Example 2 and Comparative Example 1.

Further, in Example 2, Comparative Example 1 shows the SiO ₂ concentration in the treated water after 24 hours, the experimental apparatus was stopped 2 hours, the SiO ₂ concentration in the treated water after re-activated in Table 3.

As shown in FIG. 4, in Example 2, the regeneration of sludge with acid and the second solid-liquid separation treatment are performed, and at least a portion of the second solid-liquid separated water is returned to the former stage of the first solid-liquid separation. Even when the amount of the magnesium compound (magnesium chloride) added was smaller than that of Comparative Example 1, the SiO ₂ concentration in the treated water was reduced. In Comparative Example 1, since the sludge was not regenerated, the amount of the magnesium compound (magnesium chloride) added was large.

  As shown in Table 3, in Example 2, the silica concentration of the treated water was hardly changed even if the treatment apparatus was temporarily stopped. In Comparative Example 1, when the treatment apparatus was temporarily stopped, the silica concentration of the treated water increased significantly.

  Thus, the amount of magnesium compound used in the silica treatment of silica-containing water could be reduced by the treatment apparatus and treatment method of the example.

  1,3 Treatment equipment for water containing silica, 10 treated water tanks, 12 reaction tanks, 14 coagulation tanks, 16 polymer reactors, 18 sedimentation tanks, 20 sludge regeneration tanks, 22 sludge separation tanks, 24, 26, 28 pumps, 30, 32, 34, 36 piping, 38 treated water piping, 40 sludge return piping, 42 regenerated sludge piping, 44 solid-liquid separated water return piping, 46 sludge piping, 48 magnesium compound addition piping, 50, 54 pH adjuster addition piping , 52 inorganic coagulant addition piping, 56 polymer coagulant addition piping, 58 acid addition piping, 60, 62, 64, 66 stirrer, 68 reverse osmosis membrane treatment unit, 70 permeate water piping, 72 concentrated water piping.

Claims (6)

A reaction vessel for adding a magnesium compound to water to be treated containing silica, or insolubilizing silica at a pH of 10 or more using magnesium contained in the water to be treated;
First solid-liquid separation means for solid-liquid separation of the obtained insolubilized material;
An acid addition means for adding an acid to at least a part of the sludge separated by the first solid-liquid separation means;
Second solid-liquid separation means for solid-liquid separation of the sludge to which the acid is added;
Return means for returning at least a portion of the second solid-liquid separated water separated by the second solid-liquid separation means to a front stage of the first solid-liquid separation means;
An apparatus for treating silica-containing water, comprising: The apparatus for treating silica-containing water according to claim 1, wherein
The apparatus for treating silica-containing water, characterized in that the pH of the separated sludge is adjusted to a range of 4 to 9 by adding the acid. The apparatus for treating silica-containing water according to claim 1 or 2, wherein
A silica-containing water, further comprising a reverse osmosis membrane treatment device for passing the first solid-liquid separated water through the reverse osmosis membrane to obtain permeated water and concentrated water at a stage subsequent to the first solid-liquid separation means. Processing unit. An insolubilizing step of adding a magnesium compound to the water to be treated containing silica, or insolubilizing the silica at a pH of 10 or more using magnesium contained in the water to be treated;
A first solid-liquid separation step of solid-liquid separation of the obtained insoluble matter;
An acid addition step of adding an acid to at least a part of the sludge separated in the first solid-liquid separation step;
A second solid-liquid separation step of solid-liquid separation of said acid-added sludge;
Returning at least a portion of the second solid-liquid separated water separated in the second solid-liquid separation step to a stage preceding the first solid-liquid separation step;
A method of treating silica-containing water, comprising: The method for treating silica-containing water according to claim 4,
A method of treating silica-containing water, characterized in that the pH of the separated sludge is adjusted to a range of 4 to 9 by adding the acid. The method for treating silica-containing water according to claim 4 or 5,
The silica-containing water further comprising a reverse osmosis membrane treatment step of passing the first solid-liquid separated water through the reverse osmosis membrane to obtain permeated water and concentrated water at a stage subsequent to the first solid-liquid separation step. How to handle