JP6859123B2 - Silica-containing water treatment method and its treatment equipment - Google Patents

Description

The present invention relates to a method for treating silica-containing water and a treatment device thereof.

Water treatment technology using reverse osmosis (RO) membranes has become widespread, including desalination of seawater by desalination, and application to industrial pure water production processes and wastewater recovery processes. There is. In the filtration process using a reverse osmosis membrane, the problem that silica in water is generated as scale often occurs. Specifically, as the filtration treatment by the reverse osmosis membrane progresses, the silica concentration on the concentrated water side exceeds the saturated solubility of silica, which causes silica precipitation. When silica scale is generated in this way, not only the filtration capacity of the reverse osmosis membrane is lowered, but also a big problem such as breakage of the reverse osmosis membrane may occur. Therefore, it is common to adjust the concentration ratio by the reverse osmosis membrane so that the silica concentration on the concentrated water side does not exceed the saturated solubility, but in this case, the recovery rate of water by the filtration treatment of the reverse osmosis membrane is low. Become.

Further, in a plant or the like, the circulating water used for a boiler or a cooling tower is generally used repeatedly for a certain period of time and then discharged as blow water. This is to prevent the soluble substances in water such as silica from being concentrated to generate scales due to repeated use, and the scales to be deposited in pipes and the like. In view of such a background, a method and an apparatus for efficiently reducing the silica concentration in silica-containing water are required.

Patent Documents 1 and 2 below disclose a technique for reducing the silica concentration in water by using a silica removing agent containing an iron component. In Patent Document 1 below, the silica concentration in water is reduced by adding a magnesium salt to the silica-containing water and then further adding an iron salt. Further, in Patent Document 2 below, a treatment agent containing an iron salt, an aluminum salt, a magnesium salt, or the like is added to silica-containing water to precipitate aggregates under alkaline conditions, thereby reducing the silica concentration.

Japanese Unexamined Patent Publication No. 2014-168742 Japanese Unexamined Patent Publication No. 2004-141799

The above-mentioned Patent Document 1 efficiently removes silica in water by adding two kinds of salts, a magnesium salt and an iron salt, but since the concentration of the salt used is high, the amount of sludge generated is large. More. Further, in Patent Document 2, since the concentration of iron salt is low, the amount of sludge generated is relatively small, but the silica removal rate is low. Therefore, it has been difficult to achieve a high silica removal rate while suppressing the amount of sludge generated by the conventional silica removal treatment.

The present invention has been made in view of the above problems, and an object of the present invention is a method for treating silica-containing water capable of efficiently removing silica in water while suppressing the amount of sludge generated, and a treatment apparatus thereof. Is to provide.

The method for treating silica-containing water according to one aspect of the present invention includes a raw water supply step of supplying silica-containing raw water to the reaction tank and a removing agent supply step of supplying a silica-containing silica removing agent to the reaction tank. And a pH adjusting step for adjusting the pH in the reaction vessel, and a silica removing step for removing silica contained in the raw water with the silica removing agent. The reaction vessel contains a precipitation aid having a surface area of 0.5 m ² / l or more and 1000 m ^{2 / l or less in the reaction vessel.} In the silica removal step, silica contained in raw water is removed under treatment conditions in which the pH in the reaction vessel is 6 or more and the iron concentration in the reaction vessel is 10 mg / l or more and 250 mg / l or less.

In the method for treating silica-containing water, the pH in the reaction vessel may be 10 or less in the silica removal step.

The method for treating silica-containing water may further include a solid-liquid separation step for solid-liquid separation of the treated water from which silica has been removed and taken out from the reaction vessel.

In the method for treating silica-containing water, at least a part of the precipitation aid may be in a fluid state in the raw water. In the solid-liquid separation step, solid-liquid separation may be performed by precipitating sludge contained in the treated water. The method for treating silica-containing water may further include a return step of returning at least a part of the sludge precipitated in the solid-liquid separation step to the reaction tank.

In the method for treating silica-containing water, in the solid-liquid separation step, the treated water may be solid-liquid separated by membrane filtration.

The method for treating silica-containing water may further include a filtration step of filtering the solid-liquid separated treated water with a reverse osmosis membrane.

The silica-containing water treatment apparatus according to another aspect of the present invention supplies the reaction tank, the raw water supply means for supplying the raw water containing silica to the reaction tank, and the silica removing agent containing an iron component to the reaction tank. The removing agent supply means, the pH adjusting means for supplying the pH adjusting agent to the reaction vessel, and the surface area contained in the reaction vessel in the reaction vessel of 0.5 m ² / l or more and 1000 m ² / l or less. It comprises a certain precipitation aid. The pH adjusting means is configured to supply the pH adjusting agent to the reaction vessel so that the pH in the reaction vessel becomes 6 or more. The removing agent supplying means is configured to supply the silica removing agent to the reaction tank so that the iron concentration in the reaction tank is 10 mg / l or more and 250 mg / l or less.

In the silica-containing water treatment apparatus, the pH adjusting means may be configured to supply the pH adjusting agent to the reaction vessel so that the pH in the reaction vessel becomes 10 or less.

The silica-containing water treatment apparatus may further include a means for taking out the treated water from which silica has been removed from the reaction vessel, and a solid-liquid separating means for solid-liquid separating the treated water.

In the silica-containing water treatment apparatus, at least a part of the precipitation aid may be flowable in raw water. The solid-liquid separation means may be composed of a settling tank for precipitating sludge contained in the treated water. The silica-containing water treatment apparatus may further include a return means for returning at least a part of the precipitated sludge from the settling tank to the reaction tank.

In the silica-containing water treatment apparatus, the solid-liquid separation means may be configured by a membrane filtration apparatus.

The silica-containing water treatment device may be further provided with a reverse osmosis membrane device that is arranged on the downstream side of the solid-liquid separation means and filters the solid-liquid separated treated water.

According to the present invention, it is possible to provide a method for treating silica-containing water capable of efficiently removing silica in water while suppressing the amount of sludge generated, and a treatment apparatus thereof.

It is a schematic diagram which shows the structure of the silica-containing water treatment apparatus which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the structure of the silica-containing water treatment apparatus which concerns on Embodiment 2 of this invention. It is a schematic diagram which shows the structure of the silica-containing water treatment apparatus which concerns on Embodiment 3 of this invention. It is a graph which shows the relationship between the iron concentration (mg / l) in a reaction vessel, and the silica removal rate (%). It is a graph which shows the relationship between pH in a reaction vessel and silica removal rate (%).

Hereinafter, the method for treating silica-containing water and the treatment apparatus thereof according to the embodiment of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
[Silica-containing water treatment device]
First, the configuration of the silica-containing water treatment device 1 (hereinafter, also simply referred to as “treatment device 1”) according to the first embodiment of the present invention will be described with reference to FIG. The treatment device 1 is a device for performing silica removal treatment of raw water 91 containing silica. As shown in FIG. 1, the processing apparatus 1 includes a reaction tank 10, a precipitation aid 50 contained in the reaction tank 10, a stirring means 11 for stirring the raw water 91 in the reaction tank 10, and a raw water supply means 20. , A removing agent supplying means 30, and a pH adjusting means 40.

The reaction tank 10 is a container having a tank space 10A, and the raw water 91 supplied from the raw water supply means 20 is stored in the tank space 10A. The stirring means 11 has a rotating shaft 13 and a plurality of stirring blades 12 provided at the lower ends of the rotating shaft 13, and the raw water 91 is stirred by the stirring blade 12 by rotating the rotating shaft 13 around the axis. To do.

The raw water supply means 20 supplies the raw water 91 containing silica to the reaction tank 10. Specifically, the raw water supply means 20 includes a raw water line 21 including a pipe having one end connected to the raw water inlet 10B of the reaction tank 10, a pump 23 for flowing the raw water 91 into the raw water line 21, and a raw water line 21. It can be composed of a valve 22 for switching the flow and shutoff of the raw water 91 in the inside, and a control device 24 for controlling the operation of the pump 23 and the opening and closing of the valve 22. The raw water supply means 20 is not limited to the configuration shown in FIG. 1 as long as the raw water 91 can be supplied to the reaction tank 10.

The remover supply means 30 supplies the silica remover to the reaction vessel 10. The silica removing agent contains an iron component, and the iron component is reacted with silica in the raw water 91 to form an iron-silica reactant, thereby removing the silica in the raw water 91.

The silica removing agent is not particularly limited as long as it contains iron. Examples of the silica removing agent include iron (II) chloride, iron (III) chloride, iron (II) sulfate, iron (III) sulfate, iron powder, reduced iron, iron disulfide, iron silicate, iron disilicate, and oxidation. Iron (II), iron (III) oxide, iron sulfide, iron iodide, copper chloride, polyiron sulfate, ferric chloride, iron-silica inorganic polymer flocculant and hydrates thereof can be used. it can. In particular, iron (III) chloride is preferable because it has a low cost and is less likely to be deteriorated by oxidation.

The removing agent supply means 30 can be composed of a removing agent supply line 31, a valve 32, a pump 33, a removing agent tank 34, and a control device 24. As shown in FIG. 1, one end of the remover supply line 31 is connected to the remover inlet 10C of the reaction tank 10, and the other end is connected to the remover tank 34. The remover tank 34 prepares and stores an aqueous solution of iron (III) chloride or the like. The pump 33 flows an aqueous solution of the silica removing agent through the removing agent supply line 31. The valve 32 switches the flow and cutoff of water in the remover supply line 31. The control device 24 controls the operation of the pump 33 and the opening / closing of the valve 32. The removing agent supplying means 30 may have a structure in which the silica removing agent can be supplied to the reaction tank 10, and may be, for example, a structure in which powdered iron (III) chloride is directly supplied to the reaction tank 10.

The removing agent supplying means 30 is configured to supply the silica removing agent to the reaction tank 10 so that the iron concentration in the reaction tank 10 is 10 mg / l or more and 250 mg / l or less. When the iron concentration in the reaction vessel 10 is less than 10 mg / l, it is difficult to sufficiently remove silica in the raw water 91. On the other hand, when the iron concentration in the reaction tank 10 exceeds 250 mg / l, the increase in the silica removal rate with respect to the amount of iron added becomes small, and the amount of sludge generated increases. Therefore, the removing agent supplying means 30 preferably supplies the silica removing agent so that the iron concentration in the reaction vessel 10 is 10 mg / l or more and 250 mg / l or less, and is 10 mg / l or more and 200 mg / l or less. It is more preferable to supply the silica removing agent as described above, and it is further preferable to supply the silica removing agent so as to be 20 mg / l or more and 120 mg / l or less.

The pH adjusting means 40 supplies the pH adjusting agent to the reaction vessel 10. The pH adjuster is for adjusting the pH of the raw water 91 supplied into the reaction vessel 10 to an appropriate range. As the pH adjusting agent for adjusting the pH to the acidic side (acid side pH adjusting agent), acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, citric acid or oxalic acid can be used. On the other hand, as the pH adjuster for adjusting the pH to the alkaline side (alkaline side pH adjuster), NaOH, KOH, NH ₃ water, Ca (OH) ₂ , Mg (OH) ₂ , NaOHCO ₃ or Na ₂ CO _{Bases such as 3} can be used.

When a silica removing agent is added to the raw water 91 in the reaction tank 10, the pH becomes acidic according to the amount of the silica removing agent added. At this time, an alkaline side pH adjuster is used to shift the pH to the alkaline side. The acidic pH adjuster is used to finely adjust the pH when the alkaline pH regulator is excessively added. This acidic pH adjuster can be omitted.

The pH adjusting means 40 can be composed of a pH adjusting agent supply line 41, a valve 42, a pump 43, a pH adjusting agent tank 44, and a control device 24. As shown in FIG. 1, one end of the pH regulator supply line 41 is connected to the regulator inlet 10D of the reaction tank 10, and the other end is connected to the pH regulator tank 44. The pH adjuster tank 44 prepares and stores an aqueous solution of a pH adjuster such as NaOH. The pump 43 flows an aqueous solution of the pH adjuster through the pH adjuster supply line 41. The valve 42 switches the flow and shutoff of water in the pH regulator supply line 41. The control device 24 controls the operation of the pump 43 and the opening and closing of the valve 42. The pH adjusting means 40 may be configured to directly supply solid NaOH (pH adjusting agent) to the reaction tank 10 as long as the pH adjusting agent can be supplied to the reaction tank 10.

The pH adjusting means 40 is configured to supply the pH adjusting agent to the reaction tank 10 so that the pH in the reaction tank 10 is 6 or more and 10 or less. When the pH in the reaction vessel 10 is less than 6, the saturated solubility of the reaction product of iron and silica increases, so that the silica removal rate tends to decrease. On the other hand, when the pH in the reaction tank 10 exceeds 10, the treated water taken out from the reaction tank 10 after removing the silica becomes alkaline. Therefore, when the treated water is supplied to the filtration device on the downstream side of the reaction tank 10 or when the treated water is repeatedly used, it is necessary to adjust the pH again. Therefore, the pH adjusting means 40 preferably supplies the pH adjusting agent so that the pH in the reaction vessel 10 is 6 or more and 10 or less, and supplies the pH adjusting agent so that the pH is 6 or more and 9 or less. It is more preferable to supply the pH adjuster so that the pH is 6 or more and 8 or less.

The precipitation aid 50 is water-insoluble particles and has a surface that promotes the precipitation reaction of silica by the silica removing agent. As shown in FIG. 1, the precipitation aid 50 is composed of particles having high dispersibility in water, and is in a fluidized state in raw water 91 (fluidized bed). Examples of the precipitation aid 50 include sludge generated when silica is precipitated by an iron component (silica is involved in the coagulation precipitation of iron hydroxide, or a reaction product obtained by reacting iron and silica is precipitated). Zeolite, activated charcoal, silica, filtered sand, bentonite, alumina, various carriers, water-insoluble salts, metals, active sludge and the like can be used. In particular, it is preferable to use activated sludge or zeolite as the precipitation aid 50 from the viewpoints of ease of solid-liquid separation, good fluidity, cost, and the like.

The silica-containing water treatment apparatus 1 according to the present embodiment adds the precipitation aid 50 into the reaction vessel 10 and keeps the surface area within a specific range, thereby suppressing the amount of sludge generated in the silica removal treatment. It is characterized by achieving a high silica removal rate. Here, the principle of improving the silica removal rate by the precipitation aid 50 will be described.

When the silica remover and the pH adjuster are added to the raw water 91 in the reaction vessel 10 and the precipitation aid 50 is not added, the iron derived from the silica remover functions as a positively charged flocculant. It forms flocs with the negatively charged components contained in the raw water 91 and precipitates (aggregate precipitation). Silica in the raw water 91 exists in various forms having a negative charge (for example, HSiO ₃ ⁻ , SiO ₃ ^2-, etc.). Therefore, the soluble and colloidal silica having a negative charge is potential-neutralized by the positive charge of iron, forms flocs due to the van der Waals attraction, and is precipitated and removed. In this coagulation precipitation method, the negative charge contained in the raw water 91 is neutralized, and the flocs are formed and precipitated by the van der Waals attractive force. Therefore, it is necessary to sufficiently neutralize the negative charge of silica. The amount of iron added will be large.

On the other hand, the present embodiment is different in that the iron agent is not simply used as a neutralizing agent for negative charges, but the iron agent is used as a chemical substance for causing a chemical reaction with silica in the raw water 91. ing. That is, the iron agent added to the raw water 91 chemically reacts with the silica in the raw water 91 to form a reaction product of iron and silica. This iron-silica reactant has a low saturation solubility. Therefore, it is considered that the reaction product of iron and silica in the raw water 91 is in a supersaturated state (a state in which the reaction product is dissolved in the raw water 91 more than the saturated solubility). The precipitation reaction (phase change from the liquid phase to the solid phase) in the supersaturated state generally proceeds by the following mechanism.

First, the phase change from the liquid phase to the solid phase consists of two processes, nucleation and growth. Here, depending on the state of the solution, there are cases where the nucleation phenomenon has priority and cases where the growth phenomenon of the generated nuclei has priority. Specifically, there are three states, a stable zone, a metastable zone, and an unstable zone, depending on the state of the liquid phase. The stable region is an unsaturated region, which is a region in which a phase change from a liquid phase to a solid phase does not occur. The metastable region is a region in which a nuclear growth phenomenon occurs but a new nuclear generation phenomenon does not occur. The unstable region is the region where a new nuclear phenomenon occurs.

By adding the precipitation aid 50 into the reaction vessel 10 and adjusting the surface area thereof, the surface of the precipitation aid 50 functions as a place for the nucleation and growth process of silica, and promotes the precipitation reaction of silica.

Even in the case of the coagulation precipitation method, it is presumed that iron functions as a chemical substance that causes a chemical reaction other than neutralization of negative charges and forms a reactant of iron and silica. It is considered that only the reactants up to the above-mentioned unstable zone are precipitated. However, in the present embodiment, since the precipitation aid 50 is present, even in the metastable zone where a new nucleation phenomenon does not occur, the precipitation aid 50 functions as a nucleus, so that the metastable region It is possible to precipitate and remove the reaction product of iron and silica up to (metastable zone).

As described above, the present embodiment is characterized in that even silica in the metastable region, which is a region that could not be removed by the coagulation precipitation method, can be removed. As a result, the silica removal efficiency is improved as compared with the coagulation-precipitation method, so that the silica removal rate can be increased with respect to the addition amount of the same silica remover. Therefore, since the amount of the silica removing agent added can be reduced while achieving a high silica removing rate, the amount of sludge generated can also be suppressed.

The surface area of the precipitation aid 50 in the reaction vessel 10 is 0.5 m ² / l or more and 1000 m ² / l or less in order to obtain a sufficiently practical silica precipitation reaction rate in the reaction vessel 10. When the surface area of the precipitation aid 50 is ^{less than 0.5 m 2} / l, the surface area is too small, and it is difficult to obtain a practical rate of silica precipitation reaction. On the other hand, when the surface area of the precipitation aid 50 ^{exceeds 1000 m 2} / l, the concentration of suspended pollutants (SS) in water becomes too high, which makes subsequent solid-liquid separation difficult, which is preferable for the entire water treatment system. Absent.

Therefore, the surface area of the deposition aid 50, 0.5 m ² / l or more 1000m and at ² / l or less, preferably ^2m 2 / l or more 500 meters ² / l or less, ^2m 2 / l or more 300 meters ² / It is more preferably l or less. If the surface area of the precipitation aid 50 is within this range, even silica in the metastable range can be removed within a practical time. The range of the surface area is defined because the nuclear growth reaction of silica occurs on the surface of the particles of the precipitation aid 50, and the reaction rate depends on the surface area of the precipitation aid 50.

The surface area of the precipitation aid 50 in the reaction vessel 10 can be calculated by the following formula (1).
Surface area of precipitation aid in reaction vessel (m ² / l) = Surface area of precipitation aid per unit mass (m ² / g) x amount of precipitation aid added per unit volume of reaction vessel (g / l) ... (1)
In the above formula (1), the "surface surface per unit mass of the precipitation aid (m ² / g)" is precipitated when the particles of the precipitation aid 50 are spherical and the filling rate is 68%. It is calculated using the average particle size (μm) of the auxiliary agent 50 and the bulk density (g / cm ^{3) of the precipitation auxiliary agent 50.}

^{Specifically, first, the average volume of particles 4 / 3πr 3} (r is the average particle radius) is calculated from the average particle diameter (μm) of the precipitation aid 50. Then, the reciprocal of the bulk density (mm ³ / g) of the precipitation aid 50 is divided by the average volume (mm ³ / piece) and multiplied by the filling rate (%). This makes it possible to calculate the number of particles (pieces / g) per gram of the precipitation aid 50. ^{Then, the average surface area per gram (m 2} / g) can be calculated by multiplying the number of particles per gram by ^{the average surface area (4πr 2} ) of the particles calculated from the average particle diameter (μm). ..

The average particle size of the precipitation aid 50 can be obtained, for example, by measuring the particle size distribution using SALD-7000 manufactured by Shimadzu Corporation. Specifically, the precipitation aid 50 is dispersed in water, the dispersion is measured by a light scattering method, and the mode of the particle size distribution calculated by the number conversion can be defined as the average particle size. When the precipitation aid 50 having low dispersibility in water is used, the particle size distribution can be measured using a powder tester PT-X manufactured by Hosokawa Micron Co., Ltd. In this case as well, it is preferable to define the average particle size by the mode value of the number conversion. The above-mentioned method for measuring the average particle size is an example, and other measuring methods can be adopted. The bulk density (g / cm ³ ) can be calculated by filling a container of the precipitation aid 50 in ^{a container of 10 cm 3 and measuring the weight thereof.}

The "surface area of the precipitation aid in the reaction vessel" means an effective surface area that promotes the precipitation reaction of silica (promotes the nuclear growth reaction of silica). This is different from the specific surface area measured by the BET method. Since the BET method is a method of measuring the surface area of powder by the amount of nitrogen adsorbed, the surface area in all spaces where nitrogen can enter is measured. On the other hand, the nuclear growth reaction of silica does not occur in a narrow space on the order of several nanometers where nitrogen is adsorbed, but occurs on a macroscopic surface. Therefore, in the present embodiment, the surface area of the portion where the nuclear growth reaction of silica can occur is defined as described above.

The treatment apparatus 1 further includes a take-out means 60 for taking out the treated water from which silica has been removed from the reaction tank 10, and a solid-liquid separation means 70 for solid-liquid separation of the treated water taken out from the reaction tank 10.

The take-out means 60 is composed of a take-out line having one end connected to the outlet 10E of the reaction tank 10 and the other end connected to the solid-liquid separation means 70. The treated water taken out from the reaction tank 10 is sent to the solid-liquid separating means 70 via this take-out line. The treated water contains sludge generated during the silica precipitation reaction in the reaction tank 10.

The solid-liquid separation means 70 is arranged on the downstream side (post-stage) of the reaction tank 10. In the present embodiment, the solid-liquid separation means 70 is composed of a settling tank 71. The settling tank 71 separates solid and liquid by settling the sludge contained in the treated water by gravity. Therefore, the settling tank 71 has an advantage that it is superior in energy efficiency and running cost as compared with other solid-liquid separation means. The supernatant obtained in the settling tank 71 is sent further downstream as treated water after solid-liquid separation.

The processing device 1 further includes a return means 80. As shown in FIG. 1, the return means 80 is composed of a return line connecting the bottom of the settling tank 71 and the reaction tank 10. As a result, the sludge 51 accumulated at the bottom of the solid-liquid separation in the settling tank 71 can be sent back from the settling tank 71 to the reaction tank 10 via the return line. Then, the sludge 51 sent back can be used as a precipitation aid 50 in the reaction tank 10. This reduces the need to newly add the precipitation aid 50 to the reaction tank 10, which is preferable from the viewpoint of reducing running costs. The return means 80 adjusts the return amount and the return timing of the sludge 51 so that the surface area of the precipitation aid 50 in the reaction tank 10 ^{is maintained in the range of 0.5 m 2} / l or more and 1000 m ^{2 / l or less.} It is configured as follows.

Further, the processing device 1 further includes sludge extraction means 81. The sludge extraction means 81 is connected to the bottom of the settling tank 71, whereby sludge 51 other than that returned to the reaction tank 10 among the sludge 51 accumulated at the bottom of the settling tank 71 is discharged from the settling tank 71 to the outside. can do.

[Method of treating silica-containing water]
Next, a method for treating silica-containing water according to the present embodiment, which is carried out using the silica-containing water treatment device 1, will be described.

First, the raw water 91 containing silica is supplied into the reaction tank 10 by the raw water supply means 20 (raw water supply step). Specifically, the control device 24 operates the pump 23 and opens the valve 22. As a result, the raw water 91 passes through the raw water line 21 and is supplied into the reaction tank 10 from the raw water inlet 10B. The silica concentration of the raw water 91 is, for example, 100 mg / l.

The reaction tank 10 contains a large number of precipitation aids 50 composed of particles having a surface that promotes the precipitation reaction of silica. The amount of the precipitation aid 50 added is more preferably such that the surface area of the precipitation aid 50 in the reaction vessel 10 is 0.5 m ² / l or more and 1000 m ² / l or less (preferably 2 m ² / l or more and 500 m ² / l or less). Is adjusted to be 2 m ² / l or more and 300 m ² / l or less).

Next, a silica removing agent containing an iron component (for example, iron (III) chloride) is supplied to the reaction vessel 10 by the removing agent supplying means 30 (removing agent supply step). Specifically, the control device 24 operates the pump 33 and opens the valve 32. As a result, the silica removing agent is supplied from the removing agent tank 34 to the reaction tank 10 via the removing agent supply line 31. At this time, the amount of the silica removing agent added so that the iron concentration in the reaction vessel 10 is 10 mg / l or more and 250 mg / l or less (preferably 10 mg / l or more and 200 mg / l or less, 20 mg / l or more and 120 mg / l or less). Is adjusted.

Next, the pH in the reaction vessel 10 is adjusted by supplying a pH adjusting agent such as NaOH to the reaction vessel 10 by the pH adjusting means 40 (pH adjustment step). Specifically, the control device 24 operates the pump 43 and opens the valve 42. As a result, the pH adjuster is supplied from the pH adjuster tank 44 to the reaction tank 10 via the pH adjuster supply line 41. As a result, the pH in the reaction vessel 10 is adjusted to a range of 6 or more and 10 or less.

By the above steps, as shown in FIG. 1, the reaction vessel 10 is filled with raw water 91, and the treatment conditions for removing silica (surface area of precipitation aid 0.5 to 1000 m ² / l, iron concentration 10 to 250 mg / l). l, pH 6 to 10) are prepared. Then, under this treatment condition, the silica contained in the raw water 91 is removed by the silica removing agent (silica removing step). Specifically, the iron component contained in the silica removing agent potential neutralizes the negative charge of silica to form flocs and precipitate (aggregation precipitation), and the iron component contained in the silica removing agent reacts with silica. As a result, a reaction product of iron and silica is formed, and then a reaction product of iron-silica is formed on the surface of the precipitation aid 50, whereby silica in the raw water is removed.

As described above, when only the salt such as iron is added without adding the precipitation aid 50, the silica formed by flocs is only removed by the coagulation precipitation, so that the efficiency of silica removal is insufficient. Is. On the other hand, in the present embodiment, the precipitation aid 50 is added to the reaction vessel 10 and the surface area thereof is ^{adjusted to the range of 0.5 to 1000 m 2} / l, so that silica is removed by coagulation precipitation. Not only that, but also the silica in the semi-stable region can be removed by forming an iron-silica reactant on the surface of the precipitation aid 50. Therefore, since the silica removal efficiency is improved, a high silica removal rate can be maintained even when the addition amount of the silica remover is reduced in order to suppress the amount of sludge generated.

Further, during the silica removal step, the surface area, iron concentration and pH of the precipitation aid 50 are maintained within the above ranges, respectively. Specifically, the pH in the reaction vessel 10 is monitored by the pH detection unit (pH sensor), and an appropriate amount of the pH adjuster is added at a predetermined timing by the pH adjusting means 40 so that the pH falls within the range of 6 to 10. It may be supplied to the reaction vessel 10. Further, the iron concentration in the reaction tank 10 is monitored by the concentration detection unit (concentration sensor), and an appropriate amount of silica remover is dispensed by the remover supply means 30 at a predetermined timing so that the iron concentration falls within the range of 10 to 250 mg / l. May be supplied into the reaction vessel 10.

Next, the treated water from which the silica has been removed is taken out from the reaction tank 10 and sent to the settling tank 71 (solid-liquid separation means 70) via the take-out means 60. Then, the treated water is solid-liquid separated in the settling tank 71 (solid-liquid separation step). Specifically, the sludge 51 contained in the treated water is settled on the bottom of the settling tank 71 by gravity. After that, the supernatant liquid (treated water after solid-liquid separation) from which the sludge 51 has been removed is taken out. By continuously performing the above steps, treated water from which silica has been removed can be obtained.

Further, the sludge 51 settled at the bottom of the settling tank 71 in the solid-liquid separation step is returned to the reaction tank 10 via the return means 80 (return step). The sludge 51 can be used as a precipitation aid 50 in the reaction tank 10. The precipitation aid 50 (sludge 51) is always returned in a constant amount through the return means 80 (return line). This return amount is determined so that the surface area of the precipitation aid 50 in the reaction vessel 10 is within ^{the range of 0.5 to 1000 m 2 / l.} A part of the sludge 51 separated in the settling tank 71 is pulled out by the sludge pulling means 81 (sludge pulling line). For the sludge return ratio (sludge return ratio), the SS concentration "R (mg / l)" of the sludge returned to the reaction tank 10 and the SS concentration "A (mg / l)" of 10 of the reaction tank are used. It is defined by the following formula. The sludge return ratio (%) = [A / (RA) × 100].

The return means 80 includes a valve, a pump, and the like controlled by the control device 24, and returns the sludge 51 so that ^{the surface area of the precipitation aid 50 in the reaction tank 10 falls within the range of 0.5 to 1000 m 2 / l.} It is preferable to adjust the amount. The above steps complete the method for treating silica-containing water according to the present embodiment.

[Action effect]
Next, the method for treating silica-containing water according to the present embodiment, the features of the treatment device 1 thereof, and their actions and effects will be described.

The method for treating silica-containing water according to the present embodiment includes a raw water supply step of supplying silica-containing raw water 91 to the reaction tank 10 and a removing agent supply step of supplying a silica removing agent containing an iron component to the reaction tank 10. A step of adjusting the pH in the reaction vessel 10 and a step of removing silica for removing silica contained in the raw water 91 with a silica removing agent are provided. The reaction vessel 10 contains a precipitation aid 50 having a surface area of 0.5 m ² / l or more and 1000 m ^{2 / l or less in the reaction vessel 10.} In the silica removal step, the silica contained in the raw water 91 is removed under the treatment conditions where the pH in the reaction vessel 10 is 6 or more and the iron concentration in the reaction vessel 10 is 10 mg / l or more and 250 mg / l or less.

In the silica-containing water treatment apparatus 1 according to the present embodiment, the reaction tank 10, the raw water supply means 20 for supplying the raw water containing silica to the reaction tank 10, and the silica removing agent containing an iron component are supplied to the reaction tank 10. The removing agent supply means 30 to be supplied, the pH adjusting means 40 for supplying the pH adjusting agent to the reaction tank 10, and the surface area in the reaction tank 10 contained in the reaction tank 10 is 0.5 m ² / l or more and 1000 m ² /. The precipitation aid 50, which is 1 or less, is provided. The pH adjusting means 40 is configured to supply the pH adjusting agent to the reaction tank 10 so that the pH in the reaction tank 10 becomes 6 or more. The removing agent supplying means 30 is configured to supply the silica removing agent to the reaction tank 10 so that the iron concentration in the reaction tank 10 is 10 mg / l or more and 250 mg / l or less.

According to the above characteristics, iron and silica are formed on the surface of the precipitation aid 50 by adding the precipitation aid 50 into the reaction vessel 10 ^{and adjusting the surface area thereof to 0.5 m 2} / l or more and 1000 m ^{2 / l or less.} The precipitation reaction of the reactants of the above can be promoted. As a result, unlike the usual coagulation-precipitation method, not only the silica removed by floc formation but also the silica in the metastable region can be removed, so that the silica removal efficiency can be further improved. Therefore, a high silica removal rate can be achieved even when the iron concentration is set in a relatively low range of 10 mg / l or more and 250 mg / l or less in order to reduce costs and suppress sludge generation. Therefore, according to the silica-containing water treatment method and the treatment apparatus 1 thereof according to the present embodiment, silica in the water can be efficiently removed while suppressing the amount of sludge generated.

In the above method for treating silica-containing water, the pH in the reaction vessel 10 is 10 or less in the silica removal step. In the silica-containing water treatment apparatus 1, the pH adjusting means 40 is configured to supply a pH adjusting agent to the reaction tank 10 so that the pH in the reaction tank 10 is 10 or less. As a result, neutral treated water can be taken out from the reaction tank 10, so that it is not necessary to adjust the pH again on the downstream side (post-stage) of the reaction tank 10. Therefore, unlike the case where the alkaline treated water is taken out, the cost of the acid agent required for the pH adjustment again can be reduced.

The method for treating silica-containing water includes a solid-liquid separation step of solid-liquid separating the treated water from which silica has been removed and taken out from the reaction vessel 10. The silica-containing water treatment device 1 includes a take-out means 60 for taking out the treated water from which silica has been removed from the reaction tank 10, and a solid-liquid separation means 70 for solid-liquid separation of the treated water. As a result, the sludge 51 generated in the silica removal reaction can be removed from the treated water.

In the method for treating silica-containing water, the precipitation aid 50 is in a fluid state in the raw water 91. In the solid-liquid separation step, solid-liquid separation is performed by precipitating the sludge 51 contained in the treated water. Further, the method for treating silica-containing water includes a return step of returning the sludge 51 precipitated in the solid-liquid separation step to the reaction tank 10. In the silica-containing water treatment apparatus 1, the precipitation aid 50 can flow in the raw water 91. The solid-liquid separating means 70 is composed of a settling tank 71 for precipitating sludge 51 contained in the treated water. The processing device 1 includes a return means 80 that sends the precipitated sludge 51 back from the settling tank 71 to the reaction tank 10. As a result, the sludge 51 settled at the bottom of the settling tank 71 can be returned to the reaction tank 10 and used as the precipitation aid 50. Therefore, it is less necessary to newly add the precipitation aid 50 to the reaction tank 10, and the running cost can be further reduced.

(Embodiment 2)
Next, Embodiment 2 of the present invention will be described with reference to FIG. The second embodiment is basically the same as that of the first embodiment, and has the same effect and effect, except that the solid-liquid separation means 70 is configured by the membrane filtration device 73. Hereinafter, only the differences from the first embodiment will be described.

[Silica-containing water treatment device]
As shown in FIG. 2, in the treatment device 2 according to the second embodiment, the membrane filtration device 73 is arranged on the downstream side of the reaction tank 10, and the treated water taken out from the reaction tank 10 is taken out via the take-out means 60. It is supplied to the membrane filtration device 73. As the membrane filtration device 73, for example, a casing storage type membrane module having a hollow fiber ultrafiltration (UF) membrane or a hollow fiber microfiltration (MF) membrane can be used. Further, the return means 80 and the sludge extraction means 81 are connected to the membrane filtration device 73.

[Method of treating silica-containing water]
In the second embodiment, in the solid-liquid separation step, the solid-liquid separation is performed by passing the treated water taken out from the reaction tank 10 through the membrane filtration device 73 and performing membrane filtration.

According to the second embodiment, the water quality of the treated water can be further improved as compared with the case where the settling tank 71 is used as in the first embodiment. Specifically, the SDI (silt concentration index, ASTMD4189-95) of the treated water can be lowered to 3 or less. Therefore, the treated water can be directly used as the water supply to the reverse osmosis membrane device.

(Embodiment 3)
Next, the third embodiment of the present invention will be described with reference to FIG. The third embodiment is basically the same as the second embodiment and has the same effect and effect, except that the reverse osmosis membrane device 74 is arranged. Hereinafter, only the points different from the second embodiment will be described.

[Silica-containing water treatment device]
As shown in FIG. 3, in the processing device 3 according to the third embodiment, the reverse osmosis membrane device 74 is arranged on the downstream side of the solid-liquid separation means 70 (membrane filtration device 73), and the solid-liquid separation means 70 is provided. The treated water after passing is supplied. In the reverse osmosis membrane device 74, the treated water separated by the solid-liquid separating means 70 is filtered by the reverse osmosis (RO) membrane.

[Method of treating silica-containing water]
In the third embodiment, after the solid-liquid separation step, a filtration step of filtering the solid-liquid separated treated water with an RO membrane is further performed. As a result, the water that has passed through the RO membrane is taken out from the reverse osmosis membrane device 74 as RO treated water (reference numeral 75), and the concentrated water containing impurities such as ions and salts is drained from the reverse osmosis membrane device 74 (reference numeral 75). 76). As a result, it is possible to obtain treated water having high purity from which ions and salts have been removed.

In the RO membrane, the silica concentration on the concentrated water side exceeds the saturated solubility of silica, which may cause a problem of silica scale precipitation. Therefore, in order to prevent the silica concentration on the concentrated water side from becoming too high, the recovery rate of RO treated water may be set low. On the other hand, in the present embodiment, as described above, the precipitation aid 50 can increase the silica removal efficiency in the reaction vessel 10, so that the treated water having a further reduced silica concentration is supplied to the reverse osmosis membrane apparatus 74. be able to. Therefore, even when the recovery rate of RO treated water is increased, the precipitation of silica scale in the RO membrane can be suppressed.

(Other embodiments)
Next, other embodiments of the present invention will be described.

In the first embodiment, the settling tank 71 is described as the solid-liquid separation means 70, and in the second and third embodiments, the membrane filtration device 73 is described as the solid-liquid separation means 70, but the present invention is not limited thereto. As the solid-liquid separation means 70, sand filtration, a pressurized flotation tank, a centrifuge, a vacuum dehydrator, a pressure dehydrator, a multiple disk dehydrator, a belt press, a filter press, or the like can also be adopted. It can be appropriately selected according to the above.

In the third embodiment, the settling tank 71 may be used as the solid-liquid separating means 70.

In the first to third embodiments, the case where the precipitation aid 50 adopts a fluidized bed that freely flows in the raw water 91 has been described, but the present invention is not limited to this. For example, a fixed bed may be adopted in which a table is arranged in the reaction vessel 10 and the precipitation aid 50 is fixed on the table. In this case, the process of returning the sludge 51 from the settling tank 71 to the reaction tank 10 is not adopted, and the precipitation aid 50 is replaced regularly.

Further, a fluidized bed and a fixed bed may be used in combination, and a sludge 51 return process can be adopted when at least a part of the precipitation aid 50 is used as the fluidized bed. When only the fluidized bed is adopted, it is not necessary to replace the precipitation aid 50 described above, which is preferable from the viewpoint of improving the efficiency of the process.

(Example 1)
<Raw water>
As the raw water 91 containing silica, RO concentrated water (reference numeral 76 in FIG. 3) was diluted with pure water to _{adjust the silica (SiO 2} ) concentration to 100 mg / l.

<Precipitation aid>
Iron chloride was added to an aqueous solution of 100 mg / l (SiO ₂ concentration) sodium metasilicate to adjust the iron concentration to 100 mg / l. Then, sludge was generated by adjusting the pH to 7, and this sludge was used as the precipitation aid 50.

The average particle size of the sludge was 0.3 μm when the particle size distribution was measured using SALD-7000 manufactured by Shimadzu Corporation and measured by the mode of the particle size distribution calculated by the number conversion. The bulk density of sludge was ^{calculated by filling a container of sludge in a container of 10 cm 3} and measuring the weight thereof, and it was ^{1.5 g / cm 3.} The surface area per unit mass of sludge calculated from the average particle size and bulk density was 9.1 m ² / g.

20 g of sludge was added per 1 L of the volume of the reaction tank 10 ^{to adjust the surface area of the sludge in the reaction tank 10 to 181 m 2} / l.

<Silica remover>
Iron (III) chloride was used as the silica removing agent, and the amount added was adjusted so that the iron concentration in the reaction vessel 10 was 103 mg / l.

<pH adjuster>
NaOH was used as the pH adjuster, and the amount added was adjusted so that the pH in the reaction vessel 10 became 7.0.

<Procedure for removing silica>
While the raw water 91 containing silica was supplied to the reaction tank 10 by the raw water line 21, the treated water subjected to the silica removal treatment in the reaction tank 10 was continuously taken out from the reaction tank 10. A precipitation aid 50 was added in advance into the reaction vessel 10. During this continuous treatment, iron (III) chloride is added into the reaction vessel 10 by the remover supply line 31, and NaOH is supplied to the reaction vessel 10 by the pH adjuster supply line 41 to bring the pH to 7.0. It was adjusted.

The residence time of the raw water 91 in the reaction tank 10 was about 60 minutes. The treated water continuously taken out from the reaction tank 10 was solid-liquid separated in the settling tank 71 to obtain a supernatant liquid.

<Evaluation>
The silica concentration of the treated water (supernatant) after solid-liquid separation was measured, and the silica removal rate (%) was calculated based on this measured value and the silica concentration before the treatment.

The amount of sludge generated during the silica removal treatment (mg / l) was measured.

The treated water after the solid-liquid separation was supplied again into the reaction vessel 10 in which the surface area of the sludge (precipitation aid 50) ^{was adjusted to 181 m 2 / l.} Then, the silica was allowed to stay in the reaction vessel 10 for 6 hours to promote the nuclear growth reaction of silica. Then, the silica concentration after staying for 6 hours was measured, and the silica removal rate (%) was calculated in the same manner (“Silica concentration (mg / l) of treated water” and “Silica removal rate (%)” in Table 1 below. Equivalent to).

The silica concentration and the silica removal rate after allowing the treated water to stay for 48 hours are expressed as "silica concentration (mg / l) after 48 hours and silica removal rate (%) after 48 hours" in Table 1 below. did. If no increase in the silica removal rate is observed after the residence for 48 hours, it is determined that the silica has already been removed to the metastable region by the treatment for 6 hours, and the silica removal region in Table 1 below is determined. In the item, it was set as "metastable range". On the other hand, when an increase in the silica removal rate is observed after the residence for 48 hours as compared with the case after the residence for 6 hours, it is judged that the silica is removed only to the unstable region in the treatment for 6 hours, and "No". "Stable range".

(Examples 2 to 4)
The silica removal treatment was carried out under the same conditions as in Example 1 except that the amount of iron (III) chloride added was changed as shown in Table 1 below.

(Examples 5 and 6)
The silica removal treatment was carried out under the same conditions as in Example 1 except that the pH in the reaction vessel 10 was changed as shown in Table 1 below.

(Examples 7 and 8)
The silica removal treatment was carried out under the same conditions as in Example 1 except that the surface area of the precipitation aid 50 in the reaction vessel 10 was changed as shown in Table 1 below.

(Example 9)
The silica removing treatment was carried out under the same conditions as in Example 1 except that the silica removing agent was changed to iron (II) chloride tetrahydrate.

(Example 10)
The silica removing treatment was carried out under the same conditions as in Example 1 except that the silica removing agent was changed to iron (II) sulfate heptahydrate.

(Example 11)
The silica removal treatment was carried out under the same conditions as in Example 1 except that the precipitation aid 50 was changed to filtered sand and the surface area of the precipitation aid 50 in the reaction vessel 10 was changed.

(Example 12)
The silica removal treatment was carried out under the same conditions as in Example 1 except that the precipitation aid 50 was changed to bentonite and the surface area of the precipitation aid 50 in the reaction vessel 10 was changed.

(Example 13)
The silica removal treatment was carried out under the same conditions as in Example 1 except that the pH in the reaction vessel 10 was changed as shown in Table 1 below.

(Comparative Example 1)
The silica removal treatment was carried out under the same conditions as in Example 1 except that no precipitation aid was added. That is, after performing the residence treatment for 6 hours under the condition that the precipitation aid was not added, the mixture was left for 48 hours.

(Comparative Examples 2 and 3)
The silica removal treatment was carried out under the same conditions as in Example 1 except that the amount of iron (III) chloride added was changed as shown in Table 1 below.

(Comparative Example 4)
The silica removal treatment was carried out under the same conditions as in Example 1 except that the pH in the reaction vessel 10 was changed as shown in Table 1 below.

(Comparative Example 5)
The silica removal treatment was carried out under the same conditions as in Example 1 except that ^{the surface area (m 2} / l) of the precipitation aid 50 in the reaction vessel 10 was changed as shown in Table 1 below.

Table 1 below shows the conditions and experimental results of the silica removal treatment in Examples 1 to 13 and Comparative Examples 1 to 5, respectively. FIG. 4 shows the relationship between the iron concentration (mg / l, horizontal axis) and the silica removal rate (%, vertical axis) based on the experimental results of Examples 1 to 4 and Comparative Examples 2 and 3. FIG. 5 shows the relationship between the pH (horizontal axis) and the silica removal rate (%, vertical axis) in the reaction vessel 10 based on the experimental results of Examples 1, 5, 6 and 13 and Comparative Example 4. There is.

(Discussion)
In Example 1, the silica concentration of the treated water was 38 mg / l, and the silica removal rate was 62%. This silica removal rate did not change after 48 hours. Therefore, no increase in the silica removal rate due to the nuclear growth phenomenon of silica was observed, and it was confirmed that silica was removed to the metastable region in the initial treatment.

On the other hand, in Comparative Example 1, the silica concentration of the treated water was 48 mg / l, and the silica removal rate was 52%. The silica removal rate became 62% after 48 hours, and an increase of 10% was observed. This is because the retention of 6 hours removed only the silica in the unstable region, but by extending it to 48 hours, the nuclear growth reaction proceeded over a long period of time, so that the time point of 48 hours It is considered that this is because the silica in the metastable region was also removed. From these results, it was found that a high silica removal rate can be achieved in a short treatment time by further adding the precipitation aid 50 even when the addition amount of the silica remover is the same.

As shown in FIG. 4, when the iron concentration was less than 10 mg / l (Comparative Example 3), it was impossible to remove silica. On the other hand, as the iron concentration increased, the silica removal rate and the amount of sludge generated increased. However, in the range where the iron concentration exceeds 250 mg / l, the amount of sludge generated increases at almost the same rate, whereas the increase in the silica removal rate tends to saturate. Therefore, it was found that by setting the iron concentration in the range of 10 to 250 mg / l, the amount of sludge generated can be suppressed and a high silica removal rate (62%) can be achieved.

As shown in FIG. 5, when the pH was less than 6 (Comparative Example 4), silica removal was impossible, while the silica removal rate improved as the pH shifted to the alkaline side. However, even if the pH exceeds 10, the silica removal rate hardly increases, and in this case, a neutralization treatment of the treated water is required. Therefore, it was found that the pH range is preferably 6 to 10 from the viewpoint that silica can be removed and the subsequent neutralization treatment can be omitted.

As in Comparative Example 5, in the case the surface area of the deposition aid 50 in the reaction vessel 10 is outside the range of ^{0.5~1000m 2 / l (0.3m 2 /} l), the residence time of 6 hours Only 57% silica removal rate was obtained. Therefore, it is important not only to arrange the precipitation aid 50 in the reaction vessel 10 but also ^{to adjust the surface area of the precipitation aid 50 to the range of 0.5 to 1000 m 2} / l in order to improve the silica removal efficiency. It turned out.

Since a silica removal rate of 60% was obtained in Example 9, it was found that iron (II) chloride tetrahydrate can also be used as a silica remover.

Since a silica removal rate of 58% was obtained in Example 10, it was found that iron (II) sulfate heptahydrate can also be used as a silica remover.

In Example 11, since a silica removal rate of 63% was obtained, it was found that filtered sand can also be used as the precipitation aid 50.

In Example 12, a silica removal rate of 62% was obtained, indicating that bentonite can also be used as the precipitation aid 50.

It should be understood that the embodiments and examples disclosed this time are exemplary in all respects and are not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1,2,3 Silica-containing water treatment device 10 Reaction tank 20 Raw water supply means 30 Remover supply means 40 pH adjustment means 50 Precipitation aid 51 Sludge 70 Solid-liquid separation means 71 Sedimentation tank 73 Membrane filtration device 74 Reverse osmosis membrane device 80 Return means 91 Raw water

Claims (12)

A raw water supply step that supplies silica-containing raw water to the reaction vessel,
A removal agent supply step of supplying a silica removing agent containing an iron component to the reaction vessel, and
A pH adjustment step for adjusting the pH in the reaction vessel and
A silica removing step of removing silica contained in raw water with the silica removing agent is provided.
The reaction vessel contains a precipitation aid having a surface area of 0.5 m ² / l or more and 1000 m ^{2 / l or less in the reaction vessel.}
In the silica removal step, silica contained in raw water is removed under treatment conditions in which the pH in the reaction vessel is 6 or more and the iron concentration in the reaction vessel is 10 mg / l or more and 250 mg / l or less. A method for treating silica-containing water. The method for treating silica-containing water according to claim 1, wherein the pH in the reaction vessel is 10 or less in the silica removal step. The method for treating silica-containing water according to claim 1 or 2, further comprising a solid-liquid separation step of solid-liquid separating the treated water from which silica has been removed and taken out from the reaction vessel. At least a part of the precipitation aid is in a state where it can flow in the raw water.
In the solid-liquid separation step, solid-liquid separation is performed by precipitating sludge contained in the treated water.
The method for treating silica-containing water according to claim 3, further comprising a return step of returning at least a part of the sludge precipitated in the solid-liquid separation step to the reaction vessel. The method for treating silica-containing water according to claim 3, wherein in the solid-liquid separation step, the treated water is solid-liquid separated by membrane filtration. The method for treating silica-containing water according to any one of claims 3 to 5, further comprising a filtration step of filtering the solid-liquid separated treated water with a reverse osmosis membrane. Reaction tank and
A raw water supply means for supplying raw water containing silica to the reaction vessel, and
A removing agent supplying means for supplying a silica removing agent containing an iron component to the reaction vessel,
A pH adjusting means for supplying a pH adjusting agent to the reaction vessel,
A precipitation aid contained in the reaction vessel and having a surface area of 0.5 m ² / l or more and 1000 m ² / l or less in the reaction vessel is provided.
The pH adjusting means is configured to supply the pH adjusting agent to the reaction vessel so that the pH in the reaction vessel becomes 6 or more.
The silica removing agent supply means is configured to supply the silica removing agent to the reaction vessel so that the iron concentration in the reaction vessel is 10 mg / l or more and 250 mg / l or less. Containing water treatment equipment. The silica-containing water according to claim 7, wherein the pH adjusting means is configured to supply the pH adjusting agent to the reaction vessel so that the pH in the reaction vessel becomes 10 or less. Processing equipment. A means for taking out the treated water from which silica has been removed from the reaction vessel, and
The silica-containing water treatment apparatus according to claim 7 or 8, further comprising a solid-liquid separation means for solid-liquid separation of the treated water. At least a part of the precipitation aid can flow in the raw water and
The solid-liquid separation means is composed of a settling tank for precipitating sludge contained in the treated water.
The silica-containing water treatment apparatus according to claim 9, further comprising a return means for returning at least a part of the precipitated sludge from the settling tank to the reaction tank. The silica-containing water treatment device according to claim 9, wherein the solid-liquid separation means is composed of a membrane filtration device. The silica according to any one of claims 9 to 11, further comprising a reverse osmosis membrane device arranged on the downstream side of the solid-liquid separating means and filtering the treated water separated by solid-liquid. Containing water treatment equipment.

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