JP5757110B2 - Water treatment method and water treatment system - Google Patents

Description

  The present invention relates to a water treatment method and a water treatment system using a reverse osmosis membrane module.

In the production of purified water using a reverse osmosis membrane, it is important to prevent fouling and scale generation on the primary side of the membrane in order to ensure a stable amount of permeated water (amount of fresh water). Scales are broadly classified into those mainly composed of calcium carbonate and those mainly composed of silica, but any permeation causes a decrease in the amount of permeated water.
In order to prevent the occurrence of silica-based scale, a method is known in which the pH of concentrated water is 6 or less and the silica concentration is maintained at 200 to 300 mg SiO ₂ / L (for example, see Patent Document 1).

Japanese Patent No. 3187629

However, the above-described method has a problem in that it is easy to increase the water production cost because it is necessary to constantly add an acid to the feed water for pH adjustment. Moreover, when an acid is excessively added with respect to supply water, the bicarbonate ion and carbonate ion in supply water may change to free carbonic acid (dissolved carbon dioxide gas). In this case, since free carbonic acid permeates the reverse osmosis membrane, there is a problem that the purity of purified water decreases.
Therefore, strong against purified water production that can simultaneously suppress the generation of silica-based and calcium carbonate-based scales in the reverse osmosis membrane without adding acid to the feed water or while minimizing the amount of acid added. There is a technical request.

  The present invention has been made in view of such circumstances, and the silica-based and calcium carbonate in the reverse osmosis membrane without adding an acid to the feed water or minimizing the amount of acid added. It aims at providing the water treatment method and water treatment system which can suppress generation | occurrence | production of system scale simultaneously.

The water treatment method according to the present invention is a water treatment method for purifying feed water containing silica and a hardness component, wherein a scale dispersant is added to the feed water, and a scale dispersant is added. The first reverse osmosis membrane separation step of separating the treated water into permeated water and concentrated water by the first reverse osmosis membrane module, and degassing the permeated water of the first reverse osmosis membrane separation step by the gas separation membrane module A reverse osmosis membrane separation step, characterized in that the separation operation is performed while maintaining the Langeria index of concentrated water at 0.3 or less and the silica concentration at 150 mgSiO ₂ / L or less.

Further, the water treatment system according to the present invention is a water treatment system for purifying feed water containing silica and a hardness component, and includes a dispersant addition device for adding a scale dispersant to the feed water, and a scale dispersant. A first reverse osmosis membrane module that separates the added treated water into permeated water and concentrated water; and a gas separation membrane module that degasses the permeated water separated by the first reverse osmosis membrane module. The separation operation is performed while maintaining the Langeria index of concentrated water separated by the first reverse osmosis membrane module to 0.3 or less and the silica concentration to 150 mgSiO ₂ / L or less.

According to the water treatment method and the water treatment system of the present invention, gas separation is performed by degassing dissolved gas such as free carbonic acid that cannot be removed by the first reverse osmosis membrane module from the permeated water by the gas separation membrane module at the subsequent stage. The purity of purified water (permeated water) obtained through the membrane (deaeration membrane) is increased, and the quality is improved.
In addition, by adding a scale dispersant to the feed water, the membrane surface treatment of the calcium carbonate scale is suppressed when membrane separation is performed in the first reverse osmosis membrane module in the previous stage, and a high water recovery rate (for example, 70% or more).
In addition, since the first reverse osmosis membrane module performs separation operation while maintaining the Langeria index of concentrated water at 0.3 or less and the silica concentration at 150 mg SiO ₂ / L or less, the silica concentration of the concentrated water exceeds the solubility. Moreover, precipitation can be suppressed to the RO membrane of a silica type scale.
Therefore, generation of silica-based and calcium carbonate-based scales in the reverse osmosis membrane can be simultaneously suppressed without adding an acid to the supply water or while minimizing the amount of acid added. As a result, the desired amount of fresh water can be ensured without impairing the purity of the purified water.

Moreover, the water treatment method according to the present invention may include a deionization treatment step in which the treated water in the deaeration treatment step is deionized with an electrodeionization module.
Moreover, the water treatment system which concerns on this invention WHEREIN: It is good also as including the electrodeionization module which deionizes the treated water deaerated by the said gas separation membrane module.

In this case, the treated water degassed by the gas separation membrane module can be deionized to be deionized water that is purified water with higher purity, and the quality of the purified water is improved.
In addition, since the electrodeionization module does not require so-called regeneration for maintaining the deionization performance, it is easy to handle and has a low running cost.

Moreover, the water treatment method according to the present invention may include a deionization treatment step of deionizing the treated water in the deaeration treatment step with an ion exchange resin mixed bed tower.
Moreover, the water treatment system which concerns on this invention WHEREIN: It is good also as including the ion exchange resin mixed bed tower which deionizes the treated water deaerated by the said gas separation membrane module.

In this case, the treated water degassed by the gas separation membrane module can be deionized to be deionized water that is purified water with higher purity, and the quality of the purified water is improved.
According to the present invention, not only the salt-forming cation but also the salt-forming anion that easily permeates the negatively charged RO membrane remains in the permeated water delivered from the first reverse osmosis membrane module. By deionizing these residual ions with high accuracy in the exchange resin mixed bed tower, the purity of the deionized water is sufficiently increased.

Moreover, the water treatment method according to the present invention may include a deionization process in which the treated water degassed by the gas separation membrane module is deionized by a single cation exchange resin bed tower.
Moreover, the water treatment system which concerns on this invention WHEREIN: It is good also as including the cation exchange resin single bed tower which deionizes the treated water deaerated by the said gas separation membrane module.

In this case, the treated water degassed by the gas separation membrane module can be deionized to be deionized water that is purified water with higher purity, and the quality of the purified water is improved.
Specifically, when the skin layer of the RO membrane in the first reverse osmosis membrane module is negatively charged, the permeated water separated by the RO membrane has a small residual ratio of salt constituent anions and residual salt constituent cations. A large percentage. Therefore, deionization treatment of salt constituent cations having a large residual ratio in a single cation exchange resin bed tower enables the residual ions in purified water to be accurately removed, and high-purity deionized water can be produced. Yes.
Moreover, since the initial cost of the cation exchange resin single-bed tower is low, the equipment cost can be reduced while sufficiently ensuring the quality of the deionized water.

In the water treatment method according to the present invention, the second reverse osmosis membrane separation further separates the treated water degassed by the gas separation membrane module into permeated water and concentrated water by the second reverse osmosis membrane module. It is good also as including a process.
The water treatment system according to the present invention may further include a second reverse osmosis membrane module that further separates the treated water deaerated by the gas separation membrane module into permeated water and concentrated water.

  In this case, since residual ions in the permeated water that could not be removed by the first reverse osmosis membrane module are accurately removed by the second reverse osmosis membrane module, purified water with higher purity can be produced.

Moreover, the water treatment method according to the present invention may include a deionization process in which the permeated water in the second reverse osmosis membrane separation process is deionized with an electrodeionization module.
Moreover, the water treatment system according to the present invention may include an electrodeionization module that deionizes the permeated water separated by the second reverse osmosis membrane module.

In this case, the permeated water of the second reverse osmosis membrane module can be deionized to obtain deionized water that is purified water of higher purity, and the quality of the purified water is improved.
In addition, since the electrodeionization module does not require so-called regeneration for maintaining the deionization performance, it is easy to handle and has a low running cost.

Moreover, the water treatment method according to the present invention may include a deionization treatment step in which the permeated water in the second reverse osmosis membrane separation step is deionized in an ion exchange resin mixed bed tower.
Moreover, the water treatment system according to the present invention may include an ion exchange resin mixed bed tower that deionizes the permeated water separated by the second reverse osmosis membrane module.

In this case, the permeated water of the second reverse osmosis membrane module can be deionized to obtain deionized water that is purified water of higher purity, and the quality of the purified water is improved.
According to the present invention, not only the salt cation but also the salt anion that has permeated through the negatively charged RO membrane remains in the permeate sent from the second reverse osmosis membrane module. By deionizing these residual ions with high precision in a resin mixed bed tower, the purity of deionized water is sufficiently increased.

Moreover, the water treatment method according to the present invention may include a deionization treatment step in which the permeated water in the first reverse osmosis membrane separation step is deionized using a single cation exchange resin bed tower.
Moreover, the water treatment system according to the present invention may include a single cation exchange resin bed tower that deionizes the permeated water of the first reverse osmosis membrane module.

In this case, the permeated water of the second reverse osmosis membrane module can be deionized to obtain deionized water that is purified water of higher purity, and the quality of the purified water is improved.
Specifically, when the skin layer of the RO membrane in the second reverse osmosis membrane module is negatively charged, the permeated water separated by the RO membrane has a small residual ratio of salt constituent anions and the residual salt constituent cations. A large percentage. Therefore, deionization treatment of salt constituent cations having a large residual ratio in a single cation exchange resin bed tower enables the residual ions in purified water to be accurately removed, and high-purity deionized water can be produced. Yes.
Moreover, since the initial cost of the cation exchange resin single-bed tower is low, the equipment cost can be reduced while sufficiently ensuring the quality of the deionized water.

In the water treatment method according to the present invention, the scale dispersant may be composed of a mixture of polycarboxylic acid and phosphonic acid.
In the water treatment system according to the present invention, the scale dispersant may be a mixture of polycarboxylic acid and phosphonic acid.

  By using a scale dispersant composed of a mixture of polycarboxylic acid and phosphonic acid, adhesion of calcium carbonate scale to the RO membrane surface can be effectively suppressed.

  According to the water treatment method and water treatment system of the present invention, generation of silica-based and calcium carbonate-based scales in a reverse osmosis membrane without adding an acid to supply water or while minimizing the amount of acid added. Can be suppressed simultaneously.

It is a figure showing the schematic structure of the water treatment system concerning a 1st embodiment of the present invention. It is a figure which shows the structure of the water treatment system of 1st Embodiment in detail. It is a figure explaining the structure of the Langeria index monitoring apparatus which concerns on 1st Embodiment. It is a figure which shows schematic structure of the water treatment system which concerns on 2nd Embodiment of this invention. It is a figure which shows schematic structure of the water treatment system which concerns on 3rd (4th) embodiment of this invention. It is a figure which shows schematic structure of the water treatment system which concerns on 5th Embodiment of this invention. It is a figure which shows the structure of the water treatment system of 5th Embodiment in detail. It is a figure which shows schematic structure of the water treatment system which concerns on 6th Embodiment of this invention. It is a figure which shows schematic structure of the water treatment system which concerns on 7th (8th) embodiment of this invention. It is a figure explaining the structure of the reference example of a water treatment system. It is a graph which shows the reference data regarding the water treatment system of FIG.

(First embodiment)
Hereinafter, with reference to FIGS. 1-3, the water treatment system 1 and the water treatment method which concern on 1st Embodiment of this invention are demonstrated.
FIG. 1 is a diagram illustrating a schematic configuration of a flow in the water treatment system 1 of the first embodiment, and FIGS. 2 and 3 are diagrams illustrating in detail the configuration of the water treatment system 1 of the first embodiment. .

  As shown in FIG. 1, the water treatment system 1 of the present embodiment includes a first reverse osmosis membrane module 2 that separates supply water W1 into permeate water W2 and concentrated water W3, and a first reverse osmosis membrane module. And a gas separation membrane module 3 for degassing the permeated water W2. The water treatment system 1 also includes a pH adjuster adding device 4 that adds a pH adjuster to the supply water W1 and a dispersant adding device 12 that adds a scale dispersant to the supply water W1.

The raw water (feed water W1) purified by the water treatment system 1 contains silica and hardness components (calcium ions and magnesium ions) as contaminant components. In the present application, silica means all silicas defined in “44. Silica (SiO ₂ )” of JIS K0101: 1998 “Industrial Water Test Method”.
As raw water, for example, industrial water, tap water, ground water (shallow well water, deep well water, spring water, underground water, etc.) and surface water (river water, lake water, etc.), fresh water, or factory drainage or any combination thereof The mixed water can be treated.

  Further, as shown in FIG. 2, the water treatment system 1 includes a Langeria index monitoring device 30 that monitors the Langeria index of the concentrated water W3, a silica concentration monitoring device 40 that monitors the silica concentration of the concentrated water W3, and a first And a concentrated water drain valve 15 which is a recovery rate adjusting means for adjusting the recovery rate of the reverse osmosis membrane module 2.

The first reverse osmosis membrane module 2 is not particularly limited, but includes a reverse osmosis membrane (hereinafter also referred to as “RO membrane”) in which a negatively charged skin layer made of a crosslinked wholly aromatic polyamide is formed on the membrane surface. What it has is preferable. The reverse osmosis membrane has a water permeability coefficient of 1.3 × 10 5 when a sodium chloride aqueous solution having a concentration of 500 mg / L, pH 7.0, and temperature of 25 ° C. is supplied at an operating pressure of 0.7 MPa and a recovery rate of 15%. Those having ⁻¹¹ m ³ · m ⁻² · s ⁻¹ · Pa ⁻¹ or higher and a salt removal rate of 99% or higher are preferable. Such a reverse osmosis membrane also includes a nanofiltration membrane with loose pores (having a larger water permeability coefficient).

Here, the operating pressure is an average operating pressure defined by JIS K3802-1995 “Membrane Term”. The operating pressure refers to the average value of the primary side inlet pressure and the primary side outlet pressure of the reverse osmosis membrane module.
The recovery rate refers to the ratio (%) of the flow rate (B) of the permeated water to the flow rate (A) of water (here, sodium chloride aqueous solution) supplied to the reverse osmosis membrane module (ie, B / A × 100). . The above “recovery rate 15%” is a value used as an example (standard) for defining the RO membrane to the last, and is a first reverse osmosis membrane module 2 (first reverse osmosis membrane device 11 described later). ) Is different from the “recovery rate (water recovery rate)”.
The water permeation coefficient is a value obtained by dividing the permeated water amount [m ³ / s] by the membrane area [m ² ] and the effective pressure [Pa], and is an index indicating the water permeation performance in the reverse osmosis membrane. That is, the water permeation coefficient means the amount of water that permeates the unit area of the membrane per unit time when a unit effective pressure is applied. The effective pressure is defined by JIS K3802-1995 “Membrane Term” and is a pressure obtained by subtracting the osmotic pressure difference and the secondary pressure from the operating pressure (average operating pressure).
The salt removal rate is a value calculated from the concentration of specific salts before and after permeating the membrane (here, the sodium chloride concentration), and is an index indicating the solute blocking performance in the reverse osmosis membrane. The salt removal rate is determined by (1−C ₂ / C ₁ ) × 100 from the inlet concentration (C ₁ ) and the permeated water concentration (C ₂ ) of the reverse osmosis membrane module.

  A reverse osmosis membrane satisfying the conditions of the water permeability coefficient and the salt removal rate as described above is commercially available as an RO membrane element. As the RO membrane element, for example, Toray Co., Ltd. model name “TMG20-400”, Unjin Chemical Co., Ltd. model name “RE8040-BLF”, Nitto Denko Corporation “ESPA1”, etc. can be used.

  The first reverse osmosis membrane module 2 includes a single or a plurality of RO membrane elements, and a membrane separation process is performed on the supply water W1 by the RO membrane elements to produce permeated water W2 that is highly purified water. At the same time, the concentrated water W3 in which the concentration of contaminant components in the supply water W1 is increased is produced. The shape of the RO membrane element is not particularly limited. For example, in addition to the spiral element, any of a tubular element, a hollow fiber element, a flat plate element, and a pleated element may be used.

The first reverse osmosis membrane module 2 is disposed in communication with the primary side of the RO membrane, and the water supply line W1 supplies the supply water W1 to the RO membrane, and the supply water W1 is concentrated by the RO membrane. The drainage line 6 for discharging the concentrated water W3 thus formed to the outside of the system and the secondary side of the RO membrane are disposed, and the supply water W1 is separated from the concentrated water W3 by permeating the RO membrane. A high-purity permeated water W2 is connected to a water flow line 7 for sending it to the next process.
The “line” in this specification is a general term for lines capable of flowing a fluid such as a flow path, a path, and a pipe (pipe).

A pressure pump 10 is provided on the upstream side of the first reverse osmosis membrane module 2. The pressurizing pump 10 is provided in the vicinity of the downstream end of the water flow line 5, and is configured to pressurize the feed water W <b> 1 and send it to the first reverse osmosis membrane module 2.
Thus, the water treatment system 1 is provided with the first reverse osmosis membrane device 11 including the pressure pump 10 and the first reverse osmosis membrane module 2 on the downstream side thereof.

  Although not particularly illustrated, the water treatment system 1 is provided in the water flow line 7 and detects the flow rate of the permeate W2 sent from the first reverse osmosis membrane module 2 and the rotation speed of the pressure pump 10. It is preferable to include an inverter that varies the frequency according to the output frequency and a flow rate control unit that outputs a command signal to the inverter based on a flow rate detection signal from the flow rate sensor. According to this configuration, it is possible to perform control so as to keep the flow rate of the permeate water W2 constant by feedback control based on the flow rate of the permeate water W2 detected by the flow sensor. Further, even when the treatment flow rate changes due to fluctuations in the water temperature or the like, the number of rotations of the pressure pump is automatically adjusted by the flow rate control unit, and the flow rate of the permeated water W2 can be controlled to be constant.

As shown in FIG. 2, a pH adjuster addition device 4 and a dispersant addition device 12 are connected to the water flow line 5 in order from the upstream side.
The pH adjuster addition device 4 is a device that adds a pH adjuster to the supply water W <b> 1 that flows toward the first reverse osmosis membrane module 2. The pH adjuster addition device 4 is configured to add a predetermined acidic agent (for example, hydrochloric acid or sulfuric acid), which is a pH adjuster, to the supply water W <b> 1 flowing through the water passage line 5.

  The dispersant addition device 12 is a device that adds a scale dispersant to the feed water W <b> 1 that flows toward the first reverse osmosis membrane module 2. The dispersant adding device 12 is configured to add the scale dispersant to the supply water W <b> 1 that flows through the water flow line 5. The dispersant addition device 12 adds calcium carbonate-based scale in the concentrated water W3 in the first reverse osmosis membrane module 2 (particularly, deposits on the RO membrane) by adding a scale dispersant to the supply water W1. ).

  The type of the scale dispersant is not particularly limited as long as it is water-soluble, and preferred examples include a mixture of polycarboxylic acid and phosphonic acid. A scale dispersant composed of a mixture of polycarboxylic acid and phosphonic acid is commercially available, for example, from BWA WATER ADDITIVES under the trade name “Furocon 260” (Furocon: registered trademark). This product is a 33-37% by weight aqueous solution of the mixture. Then, by adding about 1 to 5 mg / L of this aqueous solution to the supply water W1, adhesion of the calcium carbonate scale to the RO membrane surface can be effectively suppressed.

  In addition, when using an acidic chemical | medical agent (pH adjuster) and a scale dispersing agent together like this embodiment, if the acid type scale dispersing agent is used, the usage-amount of an acidic chemical | medical agent can be suppressed. As the acid-type scale dispersant, for example, polysulfonic acid can be used in addition to the above-described one.

  The gas separation membrane module 3 includes a gas separation membrane having a property of allowing the dissolved gas (gas) G to pass through without allowing the liquid to pass therethrough. This gas separation membrane includes a plurality of hollow fiber membranes having a skin layer on the surface, for example, carbon dioxide gas, oxygen from the permeated water W2 flowing outside the tubes of these hollow fiber membranes into a vacuum (depressurized) tube It is configured to deaerate dissolved gas G such as gas. As such a gas separation membrane module, for example, an external perfusion type (external pressure type) decarbonation membrane (deaeration membrane) module in which the hollow fiber membrane is made of PMP (polymethylpentene) can be used. Examples of commercially available gas separation membrane modules include DIC Corporation product names “SEPAREL EF-002A-P”, “SEPAREL EF-040P”, and the like.

  Further, the gas separation membrane module 3 is disposed on the upstream side of the gas separation membrane, and is connected to a water flow line 7 for supplying the permeated water W2 to the gas separation membrane and a decompression means (not shown) such as a vacuum pump. Next, the vent line 8 for discharging the dissolved gas G separated from the permeated water W2 by the gas separation membrane, and the treated water W4 disposed downstream of the gas separation membrane and separated from the permeated water W2 by the treated water W4 A water flow line 9 for sending out to the process is connected.

The drainage line 6 is provided with a concentrated water drainage valve 15 as a recovery rate adjusting means capable of changing the recovery rate of the first reverse osmosis membrane module 2.
As described above, the recovery rate of the first reverse osmosis membrane module 2 is obtained by the following formula (1).
Recovery [%] = permeate flow rate / (permeate flow rate + drainage flow rate) × 100 = permeate flow rate / (feed water flow rate) × 100 (1)
In the present embodiment, the drainage flow rate in the recovery rate equation (1) corresponds to the flow rate of the concentrated water W3. The water supply flow rate corresponds to the flow rate of the supply water W1. The feed water flow rate can also be obtained from the recovery rate when the permeate flow rate is constant. The water supply flow rate may be measured by providing a flow rate sensor (not shown) in the water flow line 5.

The first reverse osmosis membrane device 11 is operated with such a recovery rate set in a predetermined range. If the silica concentration of the concentrated water W3 exceeds the solubility, silica is likely to precipitate on the RO membrane surface, and therefore the recovery rate is set in a range where silica is not precipitated. In the present embodiment, the recovery rate of the first reverse osmosis membrane module 2 is set so that the silica concentration of the concentrated water W3 is 150 mgSiO ₂ / L or less.

  The concentrated water drain valve 15 adjusts the recovery rate of the first reverse osmosis membrane device 11 by opening and closing the drain line 6. Specifically, the concentrated water drain valve 15 adjusts the recovery rate of the first reverse osmosis membrane device 11 by adjusting the flow rate at which the concentrated water W3 is discharged under the condition that the flow rate of the permeated water W2 is constant. When the opening degree of the concentrated water drain valve 15 is large, the recovery rate is low because the flow rate of the concentrated water W3 is large. When the opening degree of the concentrated water drain valve 15 is small, the recovery rate is high because the flow rate of the concentrated water W3 is small.

  The concentrated water drain valve 15 is composed of, for example, a proportional control valve, and is configured to adjust the drain flow rate steplessly under the control of a silica concentration monitoring device 40 described later. The concentrated water drain valve 15 can also be configured to adjust the drain flow rate stepwise by a plurality of on-off valves such as a plurality of solenoid valves arranged in parallel with the drain line 6.

  In addition, although illustration is abbreviate | omitted, in the above-mentioned water flow line 5, 7, 9, etc., the pump which sends the water which distribute | circulates each water flow line, the valve which opens and closes a flow path, etc. are provided suitably. . These pumps and valves are controlled by a control device (not shown).

The Langeria index monitoring device 30 is a device that monitors the concentrated water W3, calculates the Langeria index of the concentrated water W3, and controls the pH adjuster addition device 4 based on the calculated Langeria index.
As shown in FIG. 3, the Langeria index monitoring device 30 includes a water quality detection device 20 as a water quality detection means, a Langeria index control unit 31, and a Langeria index storage unit 35. The Langeria index control unit 31 is electrically connected to the pH adjuster addition device 4.

  The water quality detection device 20 detects the water quality of the concentrated water W3. The water quality detection device 20 detects information about water quality used when calculating the Langeria index. Information on the detected value of the water quality detected by the water quality detection device 20 is output to a Langeria index control unit 31 described later.

  As shown in FIG. 2, the water quality detection device 20 is connected to the drainage line 6 through the sampling line 6a. In FIG. 3, the water quality detection device 20 includes a pH value sensor 21, a temperature sensor 22, an electrical conductivity sensor 23, a calcium hardness sensor 24, and a total alkalinity sensor 25.

  The detection values detected by the pH value sensor 21, the temperature sensor 22, the electrical conductivity sensor 23, the calcium hardness sensor 24, and the total alkalinity sensor 25 are detected by a Langeria index calculation unit 32 (to be described later) of the Langeria index monitoring device 30. It is used when calculating

  The pH value sensor 21 is a sensor that detects the pH value of the concentrated water W <b> 3 flowing through the drain line 6. The temperature sensor 22 is a sensor that detects the water temperature of the concentrated water W <b> 3 flowing through the drain line 6. The electrical conductivity sensor 23 is a sensor that detects the electrical conductivity of the concentrated water W <b> 3 flowing through the drain line 6.

  The calcium hardness sensor 24 is a sensor that detects the calcium hardness of the concentrated water W <b> 3 flowing through the drain line 6. As the calcium hardness sensor 24, for example, coloring when a reagent containing 2-hydroxy-1- (2′-hydroxy-4′-sulfo-1′-naphthylazo) -3-naphthoic acid (abbreviation: HSNN) is added. Thus, a colorimetric sensor for detecting calcium hardness is used. A colorimetric sensor adds a reagent to a transparent container containing a predetermined amount of sample water, and measures the color change of the sample water due to the reaction between calcium ions and HSNN from the absorbance when irradiated with light of a specific wavelength. . The colorimetric sensor measures (detects) the calcium hardness in the sample water based on the measured absorbance.

The total alkalinity sensor 25 is a sensor that detects the total alkalinity of the concentrated water W <b> 3 flowing through the drain line 6. The total alkalinity is expressed by converting the amount of alkali components such as bicarbonate, carbonate, hydroxide, etc. contained in water into the amount of calcium carbonate (CaCO ₃ ). It is referred to as consumption (pH 4.8). As the total alkalinity sensor 25, for example, a colorimetric sensor that detects the total alkalinity by color development when a reagent containing methyl orange is added is used. A colorimetric sensor adds a reagent to a transparent container containing a predetermined amount of sample water, and measures the degree of coloration of the sample water due to the reaction between the alkali component and methyl orange from the absorbance when irradiated with light of a specific wavelength. . The colorimetric sensor measures (detects) the total alkalinity in the sample water based on the measured absorbance.

The Langeria index monitoring device 30 calculates a Langeria index (hereinafter also referred to as “LSI”) of the concentrated water W3 and controls the Langeria index of the concentrated water W3 to be maintained within a predetermined range. The Langeria index is mainly used as an index for evaluating the corrosion tendency and scale tendency of water in the water system. The Langeria index (LSI) is obtained by the following equation (2).
LSI = pH-pHs (2)
Here, pH is the actual pH value of water. Moreover, pHs is a theoretical pH value when it is in an equilibrium state in which calcium carbonate is not dissolved or precipitated in water.

pHs is obtained by the following equation (3).
pHs = 9.3 + A value + B value−C value−D value (3)
Here, the A value is a correction value determined by the evaporation residue concentration. Since the evaporation residue concentration has a correlation with the electric conductivity, the evaporation residue concentration can be obtained from the electric conductivity using a predetermined conversion formula. The B value is a correction value determined by the water temperature. The C value is a correction value determined by the calcium hardness. The D value is a correction value determined by the total alkalinity. The A to D values can be obtained from the detection values of the water quality detection device 20 using a relational expression or referring to a numerical table.

  In general, the Langeria index indicates a positive (plus) value and a larger absolute value indicates that calcium carbonate is more likely to precipitate. In addition, the Langeria index is a negative (minus) value, and the smaller the absolute value, the harder the calcium carbonate precipitates. Further, when the Langeria index is 0 (zero), the calcium carbonate is in an equilibrium state where neither precipitation nor dissolution occurs. From this, when the Langeria index of the concentrated water W3 is less than 0, it is difficult to generate a calcium carbonate scale on the RO membrane surface. Conversely, when it exceeds 0, the calcium carbonate scale on the RO membrane surface. Is easy to generate.

By the way, the inventors of the present invention have found that the Langeria index is not only an index for the precipitation of calcium carbonate but also an index for the precipitation of silica. That is, it has been found through experiments and the like that when the Langeria index is adjusted to a predetermined range, the precipitation of silica can be suppressed as well as the precipitation of calcium carbonate can be suppressed.
Specifically, precipitation of calcium carbonate scale in the concentrated water W3 is suppressed by performing membrane separation treatment with the first reverse osmosis membrane device 11 while maintaining the Langeria index of the concentrated water W3 within a range of 0.3 or less. And precipitation of silica-based scale can be suppressed.

As is clear from the above equation (2), the Langeria index of the concentrated water W3 decreases as the pH of the concentrated water W3 decreases and increases as the pH increases. Therefore, the Langeria index of the concentrated water W3 can be controlled by adjusting the pH of the concentrated water W3.
Specifically, for example, the concentrated water W3 is added by adding a predetermined acidic agent (pH adjuster) to the supply water W1 supplied to the first reverse osmosis membrane device 11 using the pH adjuster adding device 4. The pH value of can be lowered.

The Langeria index controller 31 includes a Langeria index calculator 32 as a calculator for calculating the Langeria index, a Langeria index determiner 33, and a pH adjuster controller 34 as a controller for controlling the pH adjuster addition device 4. Have
The Langeria index storage unit 35 stores predetermined parameters related to the Langeria index, various tables, and the like. Information stored in the Langeria index storage unit 35 is referred to by the Langeria index control unit 31.

  The Langeria index calculation unit 32 refers to a correction table 35a (described later) stored in the Langeria index storage unit 35, and detects the water quality detection device 20 (pH value sensor 21, temperature sensor 22, electrical conductivity sensor 23, calcium hardness sensor). 24. The detected value detected by the total alkalinity sensor 25) is corrected or converted into information for calculating the Langeria index. The Langeria index calculator 32 calculates the Langeria index based on the information corrected by the Langeria index calculator 32 and the formula (2) for the Langeria index.

  The Langeria index determination unit 33 determines whether or not the Langeria index of the concentrated water W3 is 0.3 or less based on the information on the Langeria index calculated by the Langeria index calculation unit 32.

  Based on the determination result of the Langeria index determination unit 33, the pH adjuster control unit 34 adjusts the pH so that the Langeria index of the concentrated water W3 calculated by the Langeria index calculation unit 32 is maintained in a range of 0.3 or less. The regulator addition device 4 is controlled.

  The Langeria index storage unit 35 stores predetermined parameters related to the Langeria index, various tables, and the like. Specifically, the Langeria index storage unit 35 stores information on the amount of pH adjuster added by the pH adjuster adding device 4 controlled by the pH adjuster control unit 34.

  The Langeria index storage unit 35 has a correction table 35a. In the correction table 35a, the Langeria index calculation unit 32 stores the detection values detected by the water quality detection device 20 (pH value sensor 21, temperature sensor 22, electrical conductivity sensor 23, calcium hardness sensor 24, total alkalinity sensor 25). A table for correcting to the A to D values used when calculating the Langeria index is stored.

The silica concentration monitoring device 40 is a device that monitors the concentration of silica in the concentrated water W3, and controls the concentrated water drain valve 15 based on the detected silica concentration.
As shown in FIG. 2, the silica concentration monitoring device 40 includes a silica concentration sensor 26 and a silica concentration control unit 41. The silica concentration control unit 41 is electrically connected to the concentrated water drain valve 15.

  The silica concentration sensor 26 is a sensor that detects the silica concentration of the concentrated water W <b> 3 flowing through the drain line 8. The silica concentration sensor 26 is connected to a portion located on the upstream side of the concentrated water drain valve 15 in the drain line 6. Specifically, the drain line 6 is provided with a sampling line 6a on the upstream side of the concentrated water drain valve 15, and the silica concentration sensor 26 is connected to the drain line 6 through the sampling line 6a.

  As the silica concentration sensor 26, for example, a colorimetric sensor that detects the concentration by color development when a reagent containing hexaammonium heptamolybdate is added is used. The colorimetric sensor adds the reagent to a transparent container containing a predetermined amount of sample water, and measures the degree of coloration of the sample water due to the reaction between silica and hexaammonium heptamolybdate when it is irradiated with light of a specific wavelength. Measure from The colorimetric sensor is configured to measure (detect) the silica concentration in the sample water based on the measured absorbance.

  The silica concentration control unit 41 includes a silica concentration determination unit 42 and a recovery rate adjustment control unit 43 as control means for controlling the concentrated water drain valve 15.

Based on the detection value of the silica concentration sensor 26, the silica concentration determination unit 42 determines whether or not the silica concentration of the concentrated water W3 is 150 mgSiO ₂ / L or less.

Based on the determination result of the silica concentration determination unit 42, the recovery rate adjustment control unit 43 concentrates the drainage of the concentrated water so that the silica concentration of the concentrated water W3 detected by the silica concentration sensor 26 is maintained at 150 mgSiO ₂ / L or less. The opening degree of the valve 15 is controlled.
Specifically, the recovery rate adjustment control unit 43 increases the opening of the concentrated water drain valve 15 and decreases the recovery rate when the silica concentration of the concentrated water W3 exceeds 150 mgSiO ₂ / L. Control. Conversely, the silica concentration of concentrated water W3 is in the case of less than 150mgSiO ₂ / L, the silica concentration in the range not exceeding 150mgSiO ₂ / L, and controls to increase the recovery rate to the maximum.

By the way, as described above, when the silica concentration of the concentrated water W3 exceeds the solubility, the silica may be deposited on the membrane surface of the RO membrane, which may hinder the operation of the first reverse osmosis membrane device 11. The solubility of silica varies depending on the pH value of the concentrated water W3 and the water temperature conditions, but is generally calculated by a predetermined function formula. For example, the representative value of the solubility of silica is 128 mg SiO ₂ / L when the pH value is 7 and the water temperature is 25 ° C.

However, the present invention operates to maintain the Langeria index of the concentrated water W3 at 0.3 or lower and the silica concentration at 150 mgSiO ₂ / L or lower. Therefore, even when the silica concentration in the concentrated water W3 exceeds the solubility of silica (for example, the silica concentration is in the range of 128 mgSiO ₂ / L or more and 150 mgSiO ₂ / L or less), silica is deposited on the membrane surface of the RO membrane. The water treatment system 1 which suppresses this and can maintain the flow volume of the permeate W2 stably over a long period of time is realized.

Next, operation | movement of the water treatment system 1 of 1st Embodiment, ie, the water treatment method, is demonstrated with reference to FIG.1 and FIG.2.
When the water treatment system 1 is operated and a pump (not shown) is activated, water treatment is performed as described below to produce purified water.

(PH adjuster addition step)
First, an acidic agent (for example, hydrochloric acid or sulfuric acid) is added to the supply water W1 flowing through the water flow line 5 by the pH adjuster addition device 4. The supply water W1 is not subjected to water softening treatment by, for example, a water softening device, and the supply water W1 contains silica (total silica) and hardness components (calcium ions and magnesium ions) as contaminant components. Here, the addition amount of the acidic agent added to the supply water W1 from the pH adjuster addition device 4 is controlled by the Langeria index monitoring device 30 so that the Langeria index of the concentrated water W3 is 0.3 or less. However, if the addition amount of the acidic agent exceeds a predetermined value, the hydrogen carbonate ions and carbonate ions in the feed water W1 are easily converted to carbon dioxide gas, and are released into the permeate water W2 produced in the first reverse osmosis membrane separation step. Since carbonic acid remains, it is preferable that the addition amount of the acidic chemical is controlled so that the Langeria index of the concentrated water W3 becomes 0 or more.
In addition, this pH adjuster addition process may be deleted when the Langereria index of the concentrated water W3 can be controlled to 0.3 or less without adding an acidic chemical to the supply water W1.

(Dispersant addition process)
Further, a scale dispersant (for example, a mixture of polycarboxylic acid and phosphonic acid) is added to the supply water W <b> 1 that is raw water flowing through the water flow line 5 by the dispersant addition device 12. Here, the addition amount of the scale dispersant added to the feed water W1 from the dispersant addition device 12 is about 1 to 5 mg / L of the 33-37 wt% aqueous solution of the mixture with respect to the feed water W1.
In addition, a dispersing agent addition process can also be performed before a pH adjuster addition process.

(First reverse osmosis membrane separation step)
The feed water W1 that has undergone the pH adjusting agent addition step and the dispersant addition step is circulated from the water flow line 5 to the first reverse osmosis membrane device 11 and purified. That is, the first reverse osmosis membrane device 11 separates the supply water W1 into the permeated water W2 and the concentrated water W3 by the first reverse osmosis membrane module 2.
In the first reverse osmosis membrane module 2, the separation operation is performed while maintaining the Langeria index of the concentrated water W3 to 0.3 or less and the silica concentration to 150 mgSiO ₂ / L or less. Thereby, the permeated water W2 which is the purified water from which contaminant components, such as dissolved salt, were removed can be obtained.

  The permeated water W <b> 2 produced by the first reverse osmosis membrane device 11 flows into the water flow line 7. On the other hand, the concentrated water W3 produced by the first reverse osmosis membrane device 11 is drained out of the water treatment system 1 through the drain line 6 by opening and closing the concentrated water drain valve 15 as appropriate.

(Deaeration process)
The permeated water W <b> 2 produced by the first reverse osmosis membrane device 11 is supplied to the gas separation membrane module 3 through the water passage line 7. When the permeated water W2 flows through the gas separation membrane module 3, the dissolved gas G such as carbon dioxide in the permeated water W2 is deaerated. Thus, the treated water W4 from which the dissolved gas G has been degassed from the permeated water W2 is supplied to the demand point through the water passage line 9.

In the water treatment method described above, the following operation is performed.
In the water treatment system 1 of the first embodiment, the flow rate of the permeated water W2 is maintained constant by the flow rate control unit described above. That is, the flow rate control unit controls the rotation speed of the pressurizing pump 10 with an inverter while feeding back a flow rate detection signal from a flow rate sensor provided in the water flow line 7, and the flow rate of the permeated water W2 is set in advance. Control is performed to achieve the target value (constant flow control).

The water treatment system 1 controls the pH adjuster addition device 4 while performing constant flow rate control to maintain the Langeria index of the concentrated water W3 within a range of 0.3 or less, and the concentrated water drain valve 15 Is controlled so as to maintain the silica concentration of the concentrated water W3 in the range of 150 mgSiO ₂ / L or less.

  The adjustment of the Langeria index of the concentrated water W3 will be specifically described. The water quality detection device 20 detects the water quality of the concentrated water W3 flowing through the drainage line 6. The water quality detection device 20 includes a pH value sensor 21, a temperature sensor 22, an electrical conductivity sensor 23, a calcium hardness sensor 24, and a total alkalinity sensor 25, and the detected water quality information (pH value, The temperature, electrical conductivity, calcium hardness, and total alkalinity) are output to the Langeria index calculator 32 of the Langeria index controller 31.

  The Langeria index calculation unit 32 first refers to the correction table 35a of the Langeria index storage unit 35 to obtain correction values (AD values) relating to temperature, electrical conductivity, calcium hardness, and total alkalinity. And the Langeria index calculation part 32 calculates a Langeria index based on the above-mentioned Formula (2) and (3).

The Langeria index determination unit 33 determines whether the Langeria index of the concentrated water W3 is in the range of 0.3 or less.
When the Langeria index is 0.3 or less and 0 or more, the pH adjuster control unit 34 continues the addition while maintaining the addition amount of the acidic agent in the pH adjuster addition device 4 at the initial value. When the Langelia index exceeds 0.3, the pH adjuster control unit 34 increases the amount of the acidic agent added to the pH adjuster addition device 4 from the initial value. If the Langeria index is less than 0, the pH adjuster control unit 34 stops the addition of the acidic agent in the pH adjuster adding device 4.
Here, when the Langelia index is 0.3 or less, even if the silica concentration of the concentrated water W3 exceeds the solubility, the silica deposition on the membrane surface of the RO membrane is suppressed. In addition, when the Langeria index is 0.3 or less and 0 or more, the precipitation of calcium carbonate on the RO membrane surface is usually facilitated, but by adding the scale dispersant in the dispersant addition step, In this state, precipitation of calcium carbonate is suppressed.

  The adjustment of the silica concentration of the concentrated water W3 will be specifically described. The silica concentration sensor 26 detects the silica concentration of the concentrated water W3 flowing through the drain line 6. Information on the silica concentration detected by the silica concentration sensor 26 is output to the silica concentration determination unit 42 of the silica concentration control unit 41.

The silica concentration determination unit 42 determines whether the silica concentration is equal to or lower than a predetermined threshold (150 mgSiO ₂ / L) based on the silica concentration information input from the silica concentration sensor 26.
When the silica concentration of the concentrated water W3 exceeds 150 mgSiO ₂ / L, the recovery rate adjustment control unit 43 increases the opening of the concentrated water drain valve 15 and decreases the recovery rate. In addition, when the silica concentration of the concentrated water W3 is less than 150 mgSiO ₂ / L, the recovery rate adjustment control unit 43 decreases the opening of the concentrated water drain valve 15 so that the silica concentration does not exceed 150 mgSiO ₂ / L. , Increase recovery to the maximum.

  As described above, according to the water treatment system 1 of the present embodiment and the water treatment method using the water treatment system 1, dissolved gas such as free carbonic acid that cannot be removed by the first reverse osmosis membrane module 2 is removed from the downstream gas separation membrane. By degassing the permeated water W2 with the module 2, the purity of the obtained purified water (treated water W4) is increased and the quality is improved.

  Further, since the scale dispersant is added from the dispersant addition device 12 to the supply water W1, the calcium carbonate to the RO membrane when the supply water W1 is subjected to membrane separation treatment by the first reverse osmosis membrane module 2 is used. Precipitation of the system scale is effectively suppressed, and a high water recovery rate (for example, 70% or more) can be ensured.

In addition, since the first reverse osmosis membrane module 2 performs the separation operation while maintaining the Langeria index of the concentrated water W3 at 0.3 or less and the silica concentration at 150 mgSiO ₂ / L or less, the silica concentration of the concentrated water W3 has a solubility. Even if it exceeds, precipitation of a silica-type scale can be suppressed.

  Therefore, generation of silica-based and calcium carbonate-based scales can be suppressed at the same time without adding an acid to the feed water or while minimizing the amount of acid added. As a result, the desired amount of fresh water can be ensured without impairing the purity of the purified water.

  In addition, the water treatment system 1 includes a Langeria index monitoring device 30, calculates the Langeria index of the concentrated water W3 based on the detected value of the water quality of the concentrated water W3, and the Langeria index is a predetermined value (0. 3) It is comprised so that the pH adjuster addition apparatus 4 may be controlled so that it may be maintained in the following ranges. Thereby, the water treatment system 1 can maintain the Langeria index of the concentrated water W3 accurately and stably at a predetermined value or less.

  In addition, for example, when the fluctuation of the water quality of the supply water W1 is large, the pH adjuster adding device 12 can be controlled using the Langeria index as a feedback value. Thereby, it can suppress that a scale precipitates on the RO membrane surface of the 1st reverse osmosis membrane module 2. FIG.

Further, the water treatment system 1 includes a silica concentration monitoring device 40, and the silica concentration is maintained within a predetermined value (150 mgSiO ₂ / L) or less based on the detected value of the silica concentration of the concentrated water W4. Thus, the concentrated water drain valve 15 is configured to be controlled. Thereby, the water treatment system 1 can maintain the silica density | concentration of the concentrated water W3 accurately and stably below a predetermined value.

  Further, for example, when the water quality fluctuation of the supply water W1 is large, the concentrated water drain valve 15 can be controlled using the silica concentration as a feedback value. Thereby, it can suppress that a scale precipitates on the RO membrane surface of the 1st reverse osmosis membrane module 2. FIG.

(Second Embodiment)
Next, with reference to FIG. 4, the water treatment system 51 which concerns on 2nd Embodiment of this invention, and the water treatment method using the same are demonstrated. In addition, the same code | symbol is attached | subjected to the same member as above-mentioned embodiment, and the description is abbreviate | omitted.

As shown in FIG. 4, the water treatment system 51 of the present embodiment includes the gas separation membrane module 3 on each component of the water treatment system 1 described in the first embodiment and the downstream side of the water flow line 9. The deionization process (deionization process) of the treated water W4 is included.
Although not particularly shown in FIG. 4, in the water treatment system 51 of the present embodiment as well as the water treatment system 1 of the first embodiment, the pressurizing pump 10, the Langeria index monitoring device 30, the silica concentration A monitoring device 40 and a concentrated water drain valve 15 are provided (see FIG. 2). About the structure and effect of these members, since it is the same as that of what was demonstrated in 1st Embodiment, the description is abbreviate | omitted.

  The electrodeionization module 52 is connected to the downstream side of the gas separation membrane module 3 in the water passage line 9. The electrodeionization module 52 performs a membrane separation process in which the treated water W4 produced by the gas separation membrane module 3 is separated into deionized water W5 and concentrated water (not shown) by an ion exchange membrane.

  Specifically, the electrodeionization module 52 includes a demineralization chamber and a concentration chamber. The desalting chamber and the concentration chamber are formed by alternately arranging a cation exchange membrane and an anion exchange membrane. In the desalting chamber, mixed bed ion exchange resins or ion exchange fibers are accommodated. The electrodeionization module 52 circulates ions in the permeated water W2 that could not be removed by the first reverse osmosis membrane device 11 through the gas separation membrane module 3 by passing a direct current through the desalination chamber and the concentration chamber. The deionized water is removed from the treated water W4, and deionized water (high-purity purified water) W5 can be produced.

According to the water treatment system 51 and the water treatment method of the present embodiment, the same operational effects as those of the first embodiment described above can be obtained.
Furthermore, the treated water W4 of the gas separation membrane module 3 can be deionized to obtain deionized water W5, which is purified water with higher purity, and the quality of the purified water is improved.
Further, since the electrodeionization module 52 does not require so-called regeneration for maintaining the deionization performance, it is excellent in handleability and low in running cost.

As described above, when the skin layer of the RO membrane in the first reverse osmosis membrane module 2 is negatively charged, the permeated water W2 separated by the RO membrane has a small residual ratio of salt-constituting anions. The residual ratio of salt-forming cations is large. Therefore, for example, the electrodeionization module 52 may be configured to be capable of deionizing only salt-forming cations having a large residual ratio. That is, the demineralization chamber of the electrodeionization module 52 may be formed by accommodating only a cation exchange resin or a cation exchange fiber.
In this case, the initial cost of the electrodeionization module 52 can be reduced while sufficiently ensuring the quality of the deionized water W5.

(Third embodiment)
Next, with reference to FIG. 5, the water treatment system 55 which concerns on 3rd Embodiment of this invention, and the water treatment method using the same are demonstrated. In addition, the same code | symbol is attached | subjected to the same member as above-mentioned embodiment, and the description is abbreviate | omitted.

  As shown in FIG. 5, the water treatment system 55 of the present embodiment replaces the electrodeionization module 52 of the water treatment system 51 according to the second embodiment with the deionization treatment of the treated water W4 of the gas separation membrane module 3. A cation exchange resin single-bed column 56 (deionization process) is provided. Since others are the same as that of 2nd Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The cation exchange resin single bed column 56 is connected to the downstream side of the gas separation membrane module 3 in the water flow line 9. The cation exchange resin single bed column 56 is provided with an ion exchange resin bed consisting only of cation exchange resin beads in the column, and treated water W4 produced by the gas separation membrane module 3 is used as this ion exchange resin bed. By making it distribute | circulate, it is comprised so that the deionized water W5 which is purified water of high purity may be manufactured. Specifically, the cation exchange resin single-bed column 56 produces high-purity purified water by deionizing the salt-forming cations remaining in the treated water W4.

According to the water treatment system 55 and the water treatment method of the present embodiment, the same operational effects as those of the first embodiment described above can be obtained.
Furthermore, the treated water W4 of the gas separation membrane module 3 can be deionized to obtain deionized water W5, which is purified water with higher purity, and the quality of the purified water is improved.

Here, as described above, when the skin layer of the RO membrane in the first reverse osmosis membrane module 2 is negatively charged, the permeated water W2 separated by the RO membrane has a residual ratio of salt-forming anions. There are few, and the residual ratio of a salt structure cation is large. Therefore, by deionizing a salt-containing cation having a large residual ratio in the cation exchange resin single-bed column 56, residual ions in the purified water are accurately removed, and purified water with high purity can be produced. Yes.
In addition, since the initial cost of the cation exchange resin single-bed column 56 is low, the water treatment system 55 can reduce the equipment cost while sufficiently ensuring the quality of the deionized water W5.

(Fourth embodiment)
Next, with reference to FIG. 5, the water treatment system 60 which concerns on 4th Embodiment of this invention, and the water treatment method using the same are demonstrated. In addition, the same code | symbol is attached | subjected to the same member as above-mentioned embodiment, and the description is abbreviate | omitted.

  As shown in FIG. 5, the water treatment system 60 of the present embodiment includes the gas separation membrane module 3 on each component of the water treatment system 1 described in the first embodiment and on the downstream side of the water flow line 9. The ion-exchange resin mixed bed tower 61 which deionizes the treated water W4 (deionization process) is included. Since others are the same as that of 2nd Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The ion exchange resin mixed bed tower 61 is connected to the downstream side of the gas separation membrane module 3 in the water flow line 9. The ion exchange resin mixed bed column 61 includes an ion exchange resin bed made of cation exchange resin beads and anion exchange resin beads in the column, and ion-exchanges the treated water W4 produced by the gas separation membrane module 3. By flowing through the resin bed, deionized water W5, which is high-purity purified water, is produced. Specifically, the ion-exchange resin mixed bed tower 61 deionizes salt-forming cations remaining in the treated water W4 with cation-exchange resin beads, and anion exchanges salt-formed anions remaining in the treated water W4. High-purity purified water is produced by deionizing with resin beads.

According to the water treatment system 60 and the water treatment method of the present embodiment, the same operational effects as those of the first embodiment described above can be obtained.
Furthermore, the treated water W4 of the gas separation membrane module 3 can be deionized to obtain deionized water W5, which is purified water with higher purity, and the quality of the purified water is improved.
And according to this embodiment, not only the salt constituent cation but also the salt constituent anion that permeated through the negatively charged RO membrane remained in the permeated water W2 delivered from the first reverse osmosis membrane module 2. However, the residual ions are accurately deionized from the treated water W4 in the ion-exchange resin mixed bed column 61, and the purity of the deionized water W5 is sufficiently increased.

(Fifth embodiment)
Next, with reference to FIG.6 and FIG.7, the water treatment system 65 which concerns on 5th Embodiment of this invention, and the water treatment method using the same are demonstrated. FIG. 6 is a diagram for explaining in detail the configuration of the water treatment system 65 of the fifth embodiment, and FIG. 7 is a diagram for explaining the configuration of the water treatment system 65 of the fifth embodiment in detail. In addition, the same code | symbol is attached | subjected to the same member as above-mentioned embodiment, and the description is abbreviate | omitted.

As shown in FIG. 6, the water treatment system 65 of the present embodiment includes the gas separation membrane module 3 on each component of the water treatment system 1 described in the first embodiment and the downstream side of the water flow line 9. The second reverse osmosis membrane module 16 is further included for separating the treated water W4 into permeated water W6 and concentrated water W7.
Moreover, the water treatment method of this embodiment is the same as each process of the water treatment method demonstrated in 1st Embodiment, and the treated water W4 of a deaeration process process, and also the permeated water W6 by the 2nd reverse osmosis membrane module 16. And a second reverse osmosis membrane separation step that separates into concentrated water W7.

Further, as shown in FIG. 7, the water treatment system 65 includes a pH adjuster adding device 17 that adds a pH adjuster to the treated water W4, and the treated water W4 on the downstream side of the addition position of the pH adjuster adding device 17. And a pH value sensor 27 for detecting the pH value.
In the following description, the pH adjuster adding device 17 is referred to as a second pH adjuster adding device 17 in distinction from the pH adjuster adding device 4 described in the first embodiment. Further, the pH value sensor 27 is referred to as a second pH value sensor 27 in distinction from the pH value sensor 21 described in the first embodiment.

The second reverse osmosis membrane module 16 has the same configuration as the first reverse osmosis membrane module 2 described in the first embodiment. The RO membrane of the second reverse osmosis membrane module 26 is preferably the same as the RO membrane of the first reverse osmosis membrane module 2, but other RO membranes may be used. The second reverse osmosis membrane module 16 includes a single or a plurality of RO membrane elements, and the treated water W4 is subjected to membrane separation treatment by the RO membrane elements to obtain permeated water W6, which is purified water with higher purity. While manufacturing, the concentrated water W7 in which the concentration of impurities in the treated water W4 is increased is manufactured.

  Further, the second reverse osmosis membrane module 16 is disposed in communication with the primary side of the RO membrane, and the water passage line 9 for supplying the treated water W4 to the RO membrane, and the treated water W4 by the RO membrane. A concentrated water W7 is disposed in communication with the secondary side of the RO membrane, and the concentrated water W7 passes through the RO membrane. Is connected to a water flow line 14 for sending the separated permeated water W6 having high purity to the next process.

A pressure pump 18 is provided on the upstream side of the second reverse osmosis membrane module 16. The pressurizing pump 18 is provided in the vicinity of the downstream end of the water flow line 9, pressurizes the treated water W <b> 4 sent from the gas separation membrane module 3, and sends it to the second reverse osmosis membrane module 16. Is configured to do.
As described above, the water treatment system 65 is provided with the second reverse osmosis membrane device 19 including the pressure pump 18 and the second reverse osmosis membrane module 16 on the downstream side thereof.
The water treatment system 65 of this embodiment increases the purity of the permeated water W6 produced by providing the first reverse osmosis membrane device 11 and the second reverse osmosis membrane device 19 in two stages in series. Is.

As shown in FIG. 7, a second pH adjuster addition device 17 and a second pH value sensor 27 are connected to the water flow line 9.
The second pH adjuster addition device 17 is a device that adds a pH adjuster to the treated water W <b> 4 sent from the gas separation membrane module 3 toward the second reverse osmosis membrane module 16. The second pH adjuster addition device 17 is configured to add a predetermined alkaline agent (for example, sodium hydroxide) that is a pH adjuster to the treated water W <b> 4 that flows through the water passage line 9.

The second pH value sensor 27 is a sensor that detects the pH value of the treated water W <b> 4 that flows through the water passage line 9. The second pH value sensor 27 is connected to the downstream side of the addition position of the pH adjusting agent to which the second pH adjusting agent adding device 17 is connected in the water flow line 9. The second pH value sensor 27 is configured to detect the pH value of the treated water W4 to which the pH adjusting agent has been added by the second pH adjusting agent adding device 17. The pH value detected by the second pH value sensor 27 is output to the pH adjuster control unit 36.
In the following description, the pH adjuster control unit 36 is referred to as a second pH adjuster control unit 36 in distinction from the pH adjuster control unit 34 described in the first embodiment.

  Based on the pH value information detected by the second pH value sensor 27, the second pH adjuster control unit 36 maintains the pH value of the concentrated water W3 within a predetermined range (for example, the pH value is 8 or more). In addition, the second pH adjuster addition device 17 is controlled. Specifically, the addition amount of the alkaline chemical is increased so that the pH value of the concentrated water W3 is maintained within the predetermined range.

  Although not specifically shown, the water treatment system 65 is provided in the water flow line 14 and detects the flow rate of the permeated water W6 delivered from the second reverse osmosis membrane module 16, and the rotation speed of the pressure pump 18. It is preferable to include an inverter that varies the frequency according to the output frequency and a flow rate control unit that outputs a command signal to the inverter based on a flow rate detection signal from the flow rate sensor. According to this configuration, it is possible to perform control so as to keep the flow rate of the permeate water W6 constant by feedback control based on the flow rate of the permeate water W6 detected by the flow rate sensor. Further, even when the treatment flow rate changes due to fluctuations in the water temperature or the like, the rotational speed of the pressurizing pump is automatically adjusted by the flow rate control unit, and the flow rate of the permeated water W6 can be controlled to be constant.

  In addition, although illustration is abbreviate | omitted, the water supply lines 9 and 14 etc. which were mentioned above are suitably provided with the pump which sends the water which distribute | circulates through each water flow line, the valve which opens and closes a flow path, etc. These pumps and valves are controlled by a control device (not shown).

  Since the Langeria index monitoring device 30 and the silica concentration monitoring device of the water treatment system 65 in this embodiment have the same configuration as that of the first embodiment described above, the same reference numerals are given and detailed description is omitted. .

Next, with reference to FIG.6 and FIG.7, operation | movement of the water treatment system 65 of 5th Embodiment, ie, the water treatment method, is demonstrated.
When the water treatment system 65 is operated and a pump (not shown) is started, water treatment is performed as described below to produce purified water.

First, a pH adjuster addition step, a dispersant addition step, a first reverse osmosis membrane separation step, and a deaeration treatment step are performed. Since these steps are the same as those described in the first embodiment, a description thereof will be omitted.
In the following description, in order to distinguish from the pH adjusting agent adding step described in the first embodiment (pH adjusting agent adding step of adding an acidic agent to the supply water W1 by the first pH adjusting agent adding device 4), The pH adjusting agent adding step in which the alkaline agent is added to the treated water W4 by the second pH adjusting agent adding device 17 is referred to as a second pH adjusting agent adding step.

(Second pH adjuster addition step)
An alkaline agent (for example, sodium hydroxide) is added by the second pH adjuster addition device 17 to the treated water W4 that is sent from the gas separation membrane module 3 and flows through the water passage line 9. Here, the addition amount of the alkaline agent added to the treated water W4 from the second pH adjuster adding device 17 is adjusted by the second pH adjuster control unit 36 based on the pH value detected by the second pH value sensor 27. The The adjustment of the addition amount here can use, for example, feedback control.

(Second reverse osmosis membrane separation step)
The treated water W4 to which the alkaline agent has been added through the second pH adjuster addition step is circulated from the water passage line 9 to the second reverse osmosis membrane device 19 and further purified. That is, the second reverse osmosis membrane device 19 separates the treated water W4 into the permeated water W6 and the concentrated water W7 by the second reverse osmosis membrane module 16. Thereby, the permeated water W6 which is the purified water from which contaminant components, such as dissolved salt, were further removed can be obtained.

The permeated water W6 produced by the second reverse osmosis membrane device 19 is supplied to the demand point through the water passage line 14. On the other hand, the concentrated water W7 produced by the second reverse osmosis membrane device 19 flows into the water flow line 5 through the return line 13, and is mixed with the supply water W1 and reused.
The concentrated water W7 may be drained out of the water treatment system 65 through the return line 13.

The water treatment system 65 of the present embodiment is controlled by the Langeria index monitoring device 30 so that the Langeria index of the concentrated water W3 is 0.3 or less. The silica concentration monitoring device 40 controls the concentrated water W3 so that the silica concentration is 150 mgSiO ₂ / L or less. Thereby, it is suppressed that a silica-type scale deposits on the membrane surface of the RO membrane in the first reverse osmosis membrane module 2. Further, since the permeated water W2 is water in which the silica concentration of the supply water W1 is reduced to, for example, 10% or less by the first reverse osmosis membrane module 2, the RO membrane in the second reverse osmosis membrane module 16 There is no fear that silica is deposited on the film surface.

Further, in the water treatment method of the present embodiment, the following operation is performed. In addition, the detailed description is abbreviate | omitted about the operation | movement similar to the operation | movement of the water treatment method demonstrated in 1st Embodiment.
As the same operation as described above, the Langeria index monitoring device 30 monitors and controls the Langeria index (adjustment to the target Langeria index (0.3 or less) by control of the first pH adjuster addition device 12), and the silica concentration monitoring device 40. The silica concentration is monitored and controlled by the control (adjustment to the target silica concentration (150 mg SiO ₂ / L or less) by controlling the concentrated water drain valve 15).

  In the water treatment system 65 of the fifth embodiment, the flow rate of the permeated water W6 is kept constant by the flow rate control unit described above. That is, the flow rate control unit controls the rotation speed of the pressurization pump 18 with an inverter while feeding back a flow rate detection signal from a flow rate sensor provided in the water flow line 14, and the flow rate of the permeated water W 6 is set in advance. Control is performed to achieve the target value (constant flow control).

  Further, the second pH value sensor 27 detects the pH value of the treated water W4 flowing through the water passage line 9. Information on the pH value detected by the second pH value sensor 27 is output to the second pH adjuster controller 36.

Based on the pH value information input from the second pH value sensor 27, the second pH adjuster control unit 36 determines whether the pH value of the treated water W4 is within a predetermined range (for example, the pH value is 8 or more). Determine.
Further, the second pH adjuster control unit 36 controls the second pH adjuster adding device 17 based on the pH value information input from the second pH value sensor 27 to readjust the addition amount of the alkaline agent. Specifically, the addition amount of the alkaline chemical is increased or decreased so that the pH value of the treated water W4 is maintained within the predetermined range.

Here, the reason for maintaining the pH value of the treated water W4 in a predetermined range (pH value 8 or more) will be described.
In the present embodiment, when the acidic chemical is added from the first pH adjuster addition device 12 to the supply water W1 in advance, the hydrogen carbonate ions and carbonate ions in the supply water W1 change into dissolved carbon dioxide gas. There is. As a result, the amount of dissolved carbon dioxide to be removed by the gas separation membrane module 3 is relatively increased, and the dissolved carbon dioxide tends to remain in the treated water W4. As a result, the purity of the treated water W4 may be lowered. Therefore, by setting the pH value of the treated water W4 to 8 or more, the remaining dissolved carbon dioxide gas is reionized into hydrogen carbonate ions and carbonate ions. Thereby, in the second reverse osmosis membrane module 16, the dissolved carbon dioxide gas derived from the treated water W4 can be almost completely removed, and the purity of the permeated water W6 can be improved.

According to the water treatment system 65 and the water treatment method of the present embodiment, the same operational effects as those of the first embodiment described above can be obtained.
Furthermore, since contaminant components such as dissolved salts remaining in the permeated water W2 that could not be removed by the first reverse osmosis membrane module 2 are removed from the treated water W4 by the second reverse osmosis membrane module 16, the higher Permeated water W6, which is pure purified water, can be produced.
In addition, with respect to the concentrated water W7 produced by membrane separation treatment of the treated water W4 while producing high-purity purified water in this way, the water flow line 5 on the upstream side of the first reverse osmosis membrane module 2 is used. Since it is reused, the cost of fresh water is reduced.

(Sixth embodiment)
Next, with reference to FIG. 8, the water treatment system 70 which concerns on 6th Embodiment of this invention, and the water treatment method using the same are demonstrated. In addition, the same code | symbol is attached | subjected to the same member as 5th Embodiment, and the description is abbreviate | omitted.

  As shown in FIG. 9, the water treatment system 70 of the present embodiment includes a second reverse osmosis membrane on each component of the water treatment system 65 according to the fifth embodiment and on the downstream side of the water flow line 14. It includes an electrodeionization module (electrodeionization device) 52 that deionizes the permeated water W6 of the module 16 (deionization process).

  Further, the water treatment system 70 includes a second pH value sensor 27, a second pH adjuster controller 36, pressurizing pumps 10 and 18, a Langeria index monitoring device 30, and a silica concentration monitoring device according to the water treatment system 65 of the fifth embodiment. 40 and a concentrated water drain valve 15 (see FIG. 7). About the structure and effect of these members, since it is the same as that of what was demonstrated in 5th Embodiment, the description is abbreviate | omitted.

  The electrodeionization module 52 is connected to the downstream side of the second reverse osmosis membrane module 16 in the water flow line 14. The electrodeionization module 52 converts the permeated water W6 produced by the second reverse osmosis membrane module 16 (second reverse osmosis membrane device 19) into deionized water W8 and concentrated water (not shown) using an ion exchange membrane. A membrane separation treatment is performed. Since the configuration of the electrodeionization module 52 is the same as that described in the second embodiment, the description thereof is omitted.

According to the water treatment system 70 and the water treatment method of the present embodiment, the same effects as those of the fifth embodiment described above are achieved.
Furthermore, the permeated water W6 of the second reverse osmosis membrane module 16 can be deionized to obtain deionized water W8, which is purified water of higher purity, and the quality of the purified water is improved.
Further, since the electrodeionization module 52 does not require so-called regeneration for maintaining the deionization performance, it is excellent in handleability and low in running cost.

As described above, when the skin layers of the RO membranes in the first and second reverse osmosis membrane modules 2 and 16 are negatively charged, the permeated water W6 separated by the RO membranes is a salt-constituting anion. The residual ratio of the salt is small, and the residual ratio of the salt-forming cation is large. Therefore, for example, the electrodeionization module 52 may be configured to be capable of deionizing only salt-forming cations having a large residual ratio. That is, the demineralization chamber of the electrodeionization module 52 may contain only a cation exchange resin or a cation exchange fiber.
In this case, the initial cost of the electrodeionization module 52 can be reduced while sufficiently ensuring the quality of the deionized water W8.

(Seventh embodiment)
Next, with reference to FIG. 9, the water treatment system 75 which concerns on 7th Embodiment of this invention, and the water treatment method using the same are demonstrated. In addition, the same code | symbol is attached | subjected to the same member as 6th Embodiment, and the description is abbreviate | omitted.

As shown in FIG. 9, the water treatment system 75 of this embodiment replaces the electrodeionization module 52 of the water treatment system 70 according to the sixth embodiment with the permeated water W6 in the second reverse osmosis membrane separation step. A cation exchange resin single-bed column 56 for deionization (deionization process) is provided. Since others are the same as that of 6th Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.
Moreover, since the structure of the cation exchange resin single bed column 56 is the same as that of what was demonstrated in 3rd Embodiment, the description is abbreviate | omitted.

According to the water treatment system 75 and the water treatment method of the present embodiment, the same operational effects as those of the fifth embodiment described above are achieved.
Furthermore, the permeated water W6 of the second reverse osmosis membrane module 16 can be deionized to obtain deionized water W8, which is purified water of higher purity, and the quality of the purified water is improved.

Here, as described above, when the skin layer of the RO membrane in the first and second reverse osmosis membrane modules 2 and 16 is negatively charged, the permeated water W6 separated by the RO membrane has a salt structure. The residual ratio of anions is small and the residual ratio of salt-forming cations is large. Therefore, by deionizing a salt-containing cation having a large residual ratio in the cation exchange resin single-bed column 56, residual ions in the purified water are accurately removed, and purified water with high purity can be produced. Yes.
In addition, since the initial cost of the cation exchange resin single-bed column 56 is low, the water treatment system 75 can reduce the equipment cost while sufficiently ensuring the quality of the deionized water W8.

(Eighth embodiment)
Next, with reference to FIG. 9, the water treatment system 80 which concerns on 8th Embodiment of this invention, and the water treatment method using the same are demonstrated.
As shown in FIG. 9, the water treatment system 80 of the present embodiment deionizes the permeated water W6 in the second reverse osmosis membrane separation step in place of the cation exchange resin single-bed column 56 according to the seventh embodiment. An ion-exchange resin mixed bed tower 61 for processing (deionization process) is provided. Since others are the same as that of 7th Embodiment, description is abbreviate | omitted.
Moreover, since the structure of the ion exchange resin mixed bed tower 61 is the same as that of what was demonstrated in 4th Embodiment, the description is abbreviate | omitted.

According to the water treatment system 80 and the water treatment method of the present embodiment, the same effects as those of the fifth embodiment described above are achieved.
Furthermore, the permeated water W6 of the second reverse osmosis membrane module 16 can be deionized to obtain deionized water W8, which is purified water of higher purity, and the quality of the purified water is improved.
And according to this embodiment, not only the salt constituent cation but also the salt constituent anion that permeated the negatively charged RO membrane was present in the permeated water W6 delivered from the second reverse osmosis membrane module 16. However, the residual ions are accurately deionized in the ion-exchange resin mixed bed column 61, and the purity of the deionized water W8 is sufficiently increased.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above-described embodiment, in the water treatment method, the first pH adjuster adding step in which the acidic agent is added by the first pH adjuster adding device 4 and the alkaline agent is added by the second pH adjuster adding device 17. Although the 2nd pH adjuster addition process was included, it is good also as a structure which is not provided with the 1st pH adjuster addition apparatus 4 and the 2nd pH adjuster addition apparatus 17, or both. That is, in the present invention, the pH adjusting agent adding step is not essential when the Langeria index of the concentrated water W3 can be maintained in the range of 0 to 0.3 without adding the pH adjusting agent.

  Moreover, in the said embodiment, although the case where an external perfusion type (external pressure type) decarboxylation membrane (deaeration membrane) was used as a gas separation membrane of the gas separation membrane module 3, it was limited to this. Instead, for example, an internal perfusion type (internal pressure type) decarboxylation film may be used. However, the use of an external perfusion-type decarbonation membrane is more preferable because gas such as free carbonic acid in the permeated water W2 can be accurately and efficiently removed.

  Moreover, in the said embodiment, although the case where the concentrated water W3 was discharged | emitted out of the system from the drainage line 6 was explained, for example, while a part of concentrated water W3 was discharged | emitted out of the system, the remainder is made into 1st. The configuration may be such that the water is returned to the water flow line 7 on the upstream side of the one reverse osmosis membrane module 2.

  Moreover, in the said embodiment, although the water quality detection apparatus 20 demonstrated the case where the water quality of the concentrated water W3 which distribute | circulates the drainage line 6 was demonstrated, the permeated water which the water quality detection apparatus 20 distribute | circulates the water flow line 7 was demonstrated. The water quality of W2 may be detected. However, when the water quality detection device 20 is connected to the water line 7, the value detected in the water line 7 is preferably converted into the detected value of the concentrated water W 3 when detected in the drain line 6. .

Further, for example, the electrical conductivity (evaporation residue), calcium hardness and total alkalinity are estimated and calculated by multiplying the detected value of the permeated water W2 flowing through the water passage line 7 by the concentration rate of the concentrated water W3. It may be a detected value.
The temperature may be a detected value by regarding the temperature of the permeated water W2 as the temperature of the concentrated water W3.
Further, the pH value may be converted based on a relational expression between the pH value of the permeated water W2 and the pH value of the concentrated water W3 at a predetermined concentration ratio in advance by experiments or the like.
In addition, the conversion formula, the relational expression, and the like may be stored in the Langeria index storage unit 35.

Further, the water quality detection device 20 may detect the water quality of the supply water W <b> 1 flowing through the water flow line 5. However, when the water quality detection device 20 is connected to the water line 5, it is preferable to convert the value detected in the water line 5 to the detected value of the treated water W 4 when detected in the drain line 6. .
In addition, the water quality detection device 20 has both the water quality of the concentrated water W3 flowing through the water flow line 6 and the water quality of the permeated water W2 (or supply water W1) flowing through the water flow line 7 (or water flow line 5). May be configured to detect.

  In addition, one water quality detection device 20 configured by any one or more of the pH value sensor 21, the temperature sensor 22, the electrical conductivity sensor 23, the calcium hardness sensor 24, and the total alkalinity sensor 25 is connected to the drain line 6. It is comprised so that the water quality of the concentrated water W3 which distribute | circulates may be detected, and it is comprised by any one or more among the pH value sensor 21, the temperature sensor 22, the electrical conductivity sensor 23, the calcium hardness sensor 24, and the total alkalinity sensor 25. Another water quality detection device 20 may be configured to detect the water quality of the permeated water W2 (or supply water W1) flowing through the water flow line 7 (or the water flow line 5).

  In addition, the water quality detection device 20 may be configured by omitting some of the sensors. For example, the electrical conductivity (evaporation residue) is an item having a small influence on pHs. Alternatively, the electrical conductivity sensor 23 may be omitted, and a set value of electrical conductivity may be stored in the Langeria index storage unit 36, and the value may be used.

  Further, regarding the calcium hardness, when the water quality of the supply water W1 is stable, the calcium hardness sensor 24 is omitted, and the set value of the calcium hardness is stored in the Langeria index storage unit 35 and used. You may comprise as follows.

  Further, when the water quality of the supply water W1 is stable with respect to the total alkalinity, the total alkalinity sensor 25 is omitted, and the set value of the total alkalinity is stored in the Langeria index storage unit 35, and the value May be used.

  Further, regarding the silica concentration monitoring device 40, when the silica concentration of the supply water W1 is stable, the silica concentration sensor 26 is omitted, and a set value of the silica concentration of the supply water W1 is set in the silica concentration determination unit 42. You may comprise so that it may memorize | store and control the recovery rate adjustment control part 43 based on the value.

  In addition, you may combine suitably the component demonstrated by the above-mentioned embodiment of this invention. In addition, the above-described components can be replaced with well-known components without departing from the spirit of the present invention.

<Experimental example>
Experimental Examples 1-3
A test water supply adjusted to a water quality of electrical conductivity 159 mS / m, hardness 414 mg CaCO ₃ / L, silica concentration 44 mg SiO ₂ / L, total alkalinity 90 mg CaCO ₃ / L, and pH 7.6 is stored in a water supply tank, This supplied water is continuously supplied to the reverse osmosis membrane module loaded with one reverse osmosis membrane element (manufactured by Eunjin Chemical Co., Ltd. model name “RE8040-BLF”) with a pressure pump, and the permeate flow rate is 1000 L / h, the recovery was 75%, and the temperature was 25 ° C. The permeate flow rate was controlled by adjusting the number of rotations of the pressure pump. The water flow to the reverse osmosis membrane module is a cross-flow method, and a part of the concentrated water is circulated to the primary side of the pressure pump so that the circulating flow rate in the system is five times the permeate flow rate. It was. During such a feed water treatment operation, a portion of the concentrated water is periodically collected as a sample, the silica concentration of the concentrated water is approximately 135 to 150 mg SiO ₂ / L, and the electrical conductivity of the concentrated water is approximately 510 to 150. It was confirmed that it was maintained at 530 mS / m.

  In this experimental example, the pH value of the water supplied to the reverse osmosis membrane module is adjusted to 6 to 6.6 by adding sulfuric acid, so that the pH value of the concentrated water is adjusted to about 8 to 9, and the Langeria index (LSI) Were controlled to -0.2 (Experimental Example 1), 0.1 (Experimental Example 2), and 0.3 (Experimental Example 3), respectively. In addition, as a scale dispersant, a trade name “Furocon 260” (Furocon: registered trademark) of BWA WATER ADDITIVES was added to the supplied water so as to have a concentration of 2.5 mg / L.

Comparative Experiment Example 1
The feed water was treated under the same conditions as in Experimental Examples 1 to 3 except that the Langeria index of concentrated water was controlled to 0.5 by adding sulfuric acid to the feed water.

Comparative Experiment Example 2
The feed water was treated under the same conditions as in Experimental Examples 1 to 3 except that the Langerian index of the concentrated water was not controlled by adding sulfuric acid to the feed water.

Comparative Experiment Example 3
Except for the point that the Langeria index of concentrated water was controlled to 0.2 by adding sulfuric acid to the feed water, and the recovery rate was increased to increase the silica concentration of the concentrated water to about 170 mg SiO ₂ / L. The feed water was treated under the same conditions as in No. 3.

Comparative Experiment Example 4
Except that the scale dispersant was not added to the feed water, the feed water was treated under the same conditions as in Experimental Example 3 in which the Langeria index was controlled to 0.3.

Comparative Experiment Example 5
The feed water was treated under the same conditions as in Experimental Examples 1 to 3, except that the Langeria index was not controlled by adding sulfuric acid to the feed water, and the scale dispersant was not added to the feed water.

In each of Evaluation Experimental Examples 1 to 3 and Comparative Experimental Examples 1 to 5, changes in effective pressure acting on the reverse osmosis membrane element during the water treatment operation were measured over time. And the water permeation coefficient was computed for every predetermined time passage from the measured value of the effective pressure, the set value of the permeated water flow rate, and the effective membrane area of the reverse osmosis membrane element. Since the water permeability coefficient in the initial state varies somewhat depending on individual differences in the reverse osmosis membrane elements, the numerical value at the time when one hour has elapsed from the start of the water treatment operation is used as the initial value. Moreover, the electrical conductivity of the permeated water was measured after 24 hours from the start of the water treatment operation. The electrical conductivity is an index indicating the quality of the permeated water, and the lower the value, the smaller the ionic component (contaminated component) in the permeated water, that is, the better the water quality. The results are shown in Table 1. The Langerian index, the silica concentration, and the electrical conductivity of the concentrated water in the table are average values during the water treatment operation. In Comparative Experimental Example 5, the water permeation coefficient after 120 hours had dropped to less than 15% of the initial value, so the water treatment operation was stopped at this point.

  According to Table 1, in Experimental Examples 1 to 3, the water permeation coefficient after 150 hours was maintained at 96 to 97% of the initial value, and the scale adhesion of the reverse osmosis membrane element compared to Comparative Experimental Examples 1 to 5 It can be seen that occlusion is significantly suppressed. Moreover, as for Experimental Examples 1-3, the electrical conductivity of permeated water is a numerical value comparable as compared with Comparative Experimental Examples 1-5, and it turns out that the permeated water with favorable water quality is obtained. Further, in Experimental Examples 1 to 3, when the Langerian index of the concentrated water is less than 0, the electric conductivity of the permeated water tends to be slightly higher, so the Langerian index of the concentrated water is maintained at 0 or more. It can also be seen that it is preferable.

<Reference example>
Next, as a reference example of the present invention, a water treatment system 100 and a water treatment method using the same will be described with reference to FIGS. 10 and 11.

  In general, in an RO system (water treatment system) for producing purified water using a reverse osmosis membrane (RO membrane), the purity of purified water treated by a single (one-stage) reverse osmosis membrane device (RO device) is poor. If sufficient, a plurality of (for example, two-stage) RO devices are connected in series to perform water treatment. In such a multi-stage RO system, when aiming for further improvement in purity, decarbonation means and final purity are used for the purpose of removing carbonic acid components such as free carbonic acid that are difficult to remove only by water treatment with RO membranes. A polisher (ion exchange resin mixed bed tower) may be provided for the up.

As the decarboxylation means, for example, alkaline chemical injection (adding an alkaline chemical to the supply water) can be considered. In this case, due to the ionization promoting action of the carbonic acid component, hydrogen carbonate ions and carbonate ions are removed by the RO device on the downstream side, and the effect of improving purity is obtained. However, on the other hand, there is a risk of handling chemicals, and maintenance costs such as supplementing chemicals are increased.
In addition, when the polisher is provided for the purpose of increasing the purity, high-purity purified water can be obtained, but there are disadvantages in terms of cost such as chemical regeneration costs for ion exchange resins.

In view of such circumstances, the water treatment system 100 of the present reference example shown in FIG. 10 is a first reverse osmosis membrane device (RO in the figure) that separates feed water (for example, raw water) into permeate and concentrated water. Device (previous stage)), a decarbonation membrane device for degassing the permeated water of the first reverse osmosis membrane device, and a second for further separating the treated water of the decarbonation membrane device into permeated water and concentrated water A reverse osmosis membrane device (RO device in the figure (rear stage)) and a cation exchange resin single-bed tower (cationic polisher in the figure) for deionizing the permeated water of the second reverse osmosis membrane device. .
In addition, the water treatment method of the present reference example includes a first reverse osmosis membrane separation step in which feed water is separated into permeated water and concentrated water by a first reverse osmosis membrane device, and a first reverse osmosis membrane separation step. A degassing process for degassing the permeated water with a decarboxylation membrane device, and a second reverse osmosis membrane for separating the treated water of the degassing process with a second reverse osmosis membrane device into permeated water and concentrated water A separation step and a deionization treatment step of deionizing the permeated water of the second reverse osmosis membrane separation step with a cation exchange resin single-bed tower.
That is, the water treatment system 100 and the water treatment method of the present reference example have configurations similar to the water treatment system 75 and the water treatment method of the seventh embodiment described above (see FIG. 9).

  In FIG. 10, according to the water treatment system 100 and the water treatment method of the present reference example, since the decarbonation means is used instead of the alkaline chemical injection as the decarboxylation means described above, there is no danger of chemical handling, In addition, maintenance costs can be reduced.

Also, as a final purity improving means, a mixed-bed resin polisher is not used as in the prior art, but a cationic polisher is used in the present reference example, so that the purity can be improved without waste in accordance with the water quality. Further, since the reproduction cycle can be expected to be extended, it is possible to reduce the total cost as well as the initial.
Specifically, as in the water treatment system 100 shown in FIG. 10, when a plurality of RO devices are provided in series with a decarboxylation membrane device interposed therebetween, from the general property of RO membrane (negative charge), The treated water supplied to the subsequent RO device has a water quality rich in salt constituent cations. For such water quality, sufficient purity can be obtained only by using a cation exchange resin instead of using a mixed bed resin.

Here, the behavior of the multistage RO system accompanied by decarboxylation (degassing treatment) will be described in detail by the following 1-3.
1. Change in pH value of water by decarboxylation When CO ₂ is removed from water (permeated water) by decarboxylation, the pH value is increased by the following reaction.
CO ₂ + H ₂ O → (←) HCO ₃ ⁻ + H ⁺
That is, when the CO ₂ on the left side in the above equation is removed, the reaction in the above equation shifts to the left. That is, the pH value increases as H ⁺ decreases.
2. Change in chargeability of RO membrane surface depending on pH value A general RO membrane (for example, polyamide membrane) has a negative chargeability on the membrane surface, and this chargeability depends on the pH value of water on the membrane surface. That is, when the pH value increases, the negative chargeability of the membrane is further increased (ionization of carboxyl groups of the membrane is promoted).
3. Behavior of ion permeation due to RO membrane chargeability When the negative charge on the surface of the RO membrane increases, the removal rate of anions with the same sign increases, but cations with different signs can easily permeate the membrane and the removal rate is reduced. descend. In addition, this behavior becomes more prominent as the ion concentration on the film surface is lower.
Therefore, according to the above 1 to 3, the treated water in the multistage RO system with decarboxylation (permeated water that has passed through the subsequent RO device) has a water quality rich in salt constituent cations.

  As described above, according to the RO system 100 that combines the multi-stage RO device, the decarbonation membrane device, and the cation polisher as in this reference example, the production of purified water with high purity can be stably performed compared to the conventional RO system. It is possible to construct a low-cost system.

In addition, the graph shown in FIG. 11 is a test result using an alkaline chemical injection as a decarboxylation means as the purity data of the RO system using a cation polisher (that is, different from this reference example).
From this result, even when a decarbonation membrane device was used as a decarboxylation means instead of alkaline chemical injection (corresponding to this reference example), the pH value change of the permeated water obtained by the subsequent RO device (alkaline) It is considered that the same effect can be obtained.

1, 51, 55, 60, 65, 70, 75, 80 Pure water production system 2 First reverse osmosis membrane module 3 Gas separation membrane module 12 Dispersant addition device 16 Second reverse osmosis membrane module 52 Electrodeionization Module 56 Cation exchange resin single bed tower 61 Ion exchange resin mixed bed tower W1 Feed water W2 Permeated water in first reverse osmosis membrane separation step (first reverse osmosis membrane module) W3 First reverse osmosis membrane separation step ( Concentrated water of the first reverse osmosis membrane module) W4 Treated water W6 Permeated water of the second reverse osmosis membrane separation step (second reverse osmosis membrane module) W7 Second reverse osmosis membrane separation step (second reverse osmosis) Membrane module) concentrated water

Claims (18)

A water treatment method for purifying feed water containing silica and a hardness component comprising:
A dispersant addition step of adding a scale dispersant to the feed water;
A first reverse osmosis membrane separation step in which treated water to which a scale dispersant has been added is separated into permeated water and concentrated water by a first reverse osmosis membrane module;
A degassing treatment step of degassing the permeated water of the first reverse osmosis membrane separation step with a gas separation membrane module,
In the reverse osmosis membrane separation step, a water treatment method in which separation operation is performed while maintaining a Langelia index of concentrated water at 0.3 or less and a silica concentration at 150 mg SiO2 / L or less.   The water treatment method of Claim 1 including the deionization process process of deionizing the process water of a deaeration process process with an electrodeionization module.   The water treatment method of Claim 1 including the deionization process process of deionizing the process water of a deaeration process process with an ion exchange resin mixed bed tower.   The water treatment method of Claim 1 including the deionization process of deionizing the process water of a deaeration process with a cation exchange resin single bed tower.   The water treatment method according to claim 1, further comprising a second reverse osmosis membrane separation step in which the treated water in the deaeration treatment step is further separated into permeated water and concentrated water by the second reverse osmosis membrane module.   The water treatment method of Claim 5 including the deionization process process of deionizing the permeated water of a 2nd reverse osmosis membrane separation process with an electrodeionization module.   The water treatment method according to claim 5, comprising a deionization treatment step of deionizing the permeated water in the second reverse osmosis membrane separation step with an ion exchange resin mixed bed tower.   The water treatment method according to claim 5, comprising a deionization treatment step of deionizing the permeated water in the second reverse osmosis membrane separation step with a cation exchange resin single-bed tower.   The water treatment method according to any one of claims 1 to 8, wherein the scale dispersant comprises a mixture of polycarboxylic acid and phosphonic acid. A water treatment system for purifying feed water comprising silica and hardness components comprising:
A dispersant addition device for adding a scale dispersant to the feed water;
A first reverse osmosis membrane module that separates treated water to which a scale dispersant has been added into permeate and concentrated water;
A gas separation membrane module for degassing the permeated water separated by the first reverse osmosis membrane separation module,
A water treatment system configured to perform a separation operation while maintaining a Langelia index of concentrated water separated by the first reverse osmosis membrane module at 0.3 or less and a silica concentration at 150 mg SiO2 / L or less.   The water treatment system according to claim 10, comprising an electrodeionization module that deionizes the treated water degassed by the gas separation membrane module.   The water treatment system according to claim 10, comprising an ion exchange resin mixed bed tower for deionizing treated water degassed by the gas separation membrane module.   The water treatment system of Claim 10 containing the cation exchange resin single bed tower which deionizes the treated water deaerated by the said gas separation membrane module.   The water treatment system according to claim 10, further comprising a second reverse osmosis membrane module that separates the treated water degassed by the gas separation membrane module into permeated water and concentrated water.   The water treatment system of Claim 14 containing the electrodeionization module which deionizes the permeated water isolate | separated with the said 2nd reverse osmosis membrane module.   The water treatment system according to claim 14, comprising an ion-exchange resin mixed bed tower for deionizing the permeated water separated by the second reverse osmosis membrane module.   The water treatment system of Claim 14 including the cation exchange resin single bed tower which deionizes the permeated water isolate | separated by the said 2nd reverse osmosis membrane module.   The water treatment system according to any one of claims 10 to 17, wherein the scale dispersant is composed of a mixture of polycarboxylic acid and phosphonic acid.

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