JP2006075667A - Operation method of semipermeable membrane apparatus and semipermeable membrane apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical fresh water manufacturing method capable of obtaining fresh water of high quality by efficiently removing boron using a semipermeable membrane, and a fresh water making apparatus. <P>SOLUTION: When raw water is treated using a first semipermeable membrane and the transmitted water due to the first semipermeable membrane is treated using a second semipermeable membrane device to obtain fresh water, the raw water is refluxed to the first semipermeable membrane while changing the inhibitor rates of the first semipermeable membrane and the second semipermeable membrane so that the concentration of a specific component of the concentrated water of the second semipermeable membrane becomes lower than that of the raw water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semipermeable membrane device capable of efficiently obtaining high quality fresh water from raw water using a reverse osmosis membrane (semipermeable membrane), and a method for operating the same, and more specifically, boron which is contained in seawater and is not easily removed. The present invention relates to a method for operating a semipermeable membrane device and a semipermeable membrane device that are suitable for removing water.

  In recent years, the depletion of water resources has become serious, and the utilization of water resources that have not been used is being studied. In particular, so-called “seawater desalination”, which is the most familiar technology for producing drinking water from seawater that could not be used as it is, has been attracting attention. Seawater desalination has been put to practical use mainly in the Middle East region, where water resources are extremely small and oil heat resources are extremely abundant, but the heat source is not as abundant as in the Middle East. In other areas, energy-efficient reverse osmosis is used, and many plants have been built and put into practical use in the Caribbean and Mediterranean areas. Recently, improvement in reliability and cost reduction have progressed due to technological advances in reverse osmosis, and many reverse osmosis seawater desalination plants have begun to be built in the Middle East.

  However, since the evaporation method is composed of evaporation and condensation of water, the water obtained theoretically does not contain solid components, whereas the reverse osmosis method is separation by sieving through the molecular gap of the membrane, so Solute prevention is difficult. In other words, the reverse osmosis method is essentially difficult to be superior in water quality to the evaporation method, and even with the recently improved desalination performance of reverse osmosis membranes, it depends on operating conditions and water quality standards. Does not satisfy sufficient removal performance for all components.

  In particular, about 4.5 mg of boron contained in seawater has adverse effects on plant growth and problems such as infertility, and drinking water guidelines with a WHO of 0.5 mg / l or less have been established. In Japan, a water quality standard value of 1.0 mg / l or less was set in 2003, but in normal seawater, it exists as non-dissociated boric acid, so the electrical surface on the membrane surface There is no mechanical repulsive force, and the blocking performance is low compared to other salts. Removal of boron is regarded as the biggest problem in seawater desalination using the current reverse osmosis membrane.

  Therefore, in order to increase the boron removal rate, a multi-stage process (non-stage method) is combined with a permeated water two-stage method (Patent Document 1) in which the permeate is treated again with a low-pressure reverse osmosis membrane and a post-treatment in which a boron adsorbent is passed. Patent Document 1) is adopted. However, although a high removal rate can be obtained, the boron adsorbent has a problem in cost, and even in a two-stage treatment with a low pressure reverse osmosis membrane, it can be operated at a lower cost than the boron adsorbent (Non-patent Document 2). While the adsorbent can treat seawater with a reverse osmosis membrane and collect almost all of the permeated water, the two-stage treatment with a low-pressure reverse osmosis membrane, in principle, discharges concentrated water. However, since this concentrated water generally has a lower osmotic pressure than seawater, a method is adopted in which the concentrated water is recirculated and mixed with seawater and used as raw water (Patent Document 2).

  As a method for reducing the boron concentration with a reverse osmosis membrane, an alkali addition method has been proposed in which the raw water in the second stage is raised to pH 9.5 or higher to dissociate boron into borate ions to increase the removal rate (Patent Document 3). ) Has been put to practical use. However, this alkali addition method is limited in its pH adjustment operation due to the problems of the alkali resistance of the reverse osmosis membrane used and the increase in operating cost due to an increase in the amount of chemicals. For example, in the case of polyamide-based semipermeable membranes, those having excellent high pH durability have been developed recently, but in general, continuous operation at pH 10 or higher is difficult. Furthermore, if the pH becomes too high, the removal performance of the total salt concentration is abruptly reduced, leading to a decrease in water quality. In addition, as in the Middle East, it contains a high concentration of solute (total salt concentration 4 to 5% by weight, boron concentration 5 to 7 mg / l), and pH 10 in harsh environments such as the summer high temperature period (30 to 40 ° C.) Even boron cannot be removed sufficiently.

  For this reason, a special boron removal process such as a special four-stage method (Patent Document 4) has been proposed, but there is a problem that the process is complicated, and it is not easy to control fluctuations in operating conditions such as seasonal fluctuations. There's a problem.

Although a method of adding alkali to the first stage of the reverse osmosis membrane is also conceivable, the recovery rate of the first stage is lower than that of the second stage. Will take.
Therefore, if the boron removal performance at the first stage is low, the pH at the second stage needs to be very high, but since the pH is a logarithm of the hydrogen ion concentration, the chemical input required for pH adjustment increases the pH. Exponentially increases with time. Further, the fact that the first stage cannot be sufficiently removed means that the concentration of the feed water in the second stage is high, and this means that the concentration of the second stage concentrated water refluxed in the first stage is increased.
That is, depending on the removal performance of the first-stage and second-stage reverse osmosis membranes, there is a problem that the concentration of boron in the second-stage concentrated water is higher than that of seawater. As a result, the load on the reverse osmosis membrane was increased, and as a result, the quality of the final treated water was deteriorated.
This is true not only for boron but also for various salinities. In the case of a hardness component, the scale is likely to precipitate.
JP 2001-269543 A (paragraphs [0038] to [0039]) JP-A-9-10766 (paragraph [0009]) Japanese Patent No. 3319321 (paragraphs [0006] to [0013]) International Publication No. 02/068338 Pamphlet (1st page abstract) J. et al. J. Redondo et al., Desalination, 156, 2003, p229-238. Y. Y. Fusaoka, M. Taniguchi et al., Boron removal in seawater RO desalination, EDS 2004 draft

  The object of the present invention is to solve the above-mentioned problems, and even when the raw water has a high concentration and high temperature, boron can be efficiently removed using a semipermeable membrane, and high quality fresh water can be obtained. The object is to provide a practical method for operating a fresh water production apparatus and a fresh water production apparatus.

The present invention for solving the above-described problems is characterized by the following (1) to (11).
(1) Raw water is treated with the first semipermeable membrane unit, the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain permeated water, and the second semipermeable membrane is used. In the operation method of the semipermeable membrane device capable of refluxing and mixing at least a part of the concentrated water of the membrane unit to the raw water of the first semipermeable membrane unit, the specific component concentration of the concentrated water of the second semipermeable membrane unit A method for operating a semipermeable membrane device, wherein the blocking rate of specific components of the first semipermeable membrane unit and the second semipermeable membrane unit is changed so that the concentration of the semipermeable membrane unit is lower than that of the raw water.

  (2) The method for changing the rejection rate is the control of the recovery rate, which is the permeate flow rate relative to the raw water flow rate, or at least one temperature, pH, or flow rate selected from raw water, permeate water, and concentrated water. The operation method of the semipermeable membrane device according to (1), characterized by being controlled.

(3) The recovery rate of the first semipermeable membrane unit is R ₁ , the rejection rate of the specific component is r ₁ , the recovery rate of the second semipermeable membrane unit is R ₂ , and the rejection rate of the specific component is r ₂ . When

The method for operating the semipermeable membrane device according to (1) or (2), wherein:

  (4) The method for operating a semipermeable membrane device according to (1) or (2), wherein the raw water is seawater or saltwater pretreated from seawater.

(5) Method of operating a semipermeable membrane device in which raw water is treated with a first semipermeable membrane unit, and the permeated water from the first semipermeable membrane unit is treated with a second semipermeable membrane unit to obtain permeated water. , The rejection rate of the specific component of the first semipermeable membrane unit is r ₁ , the rejection rate of the specific component of the second semipermeable membrane unit is r ₂ , the raw water concentration is C _F , and the target permeated water concentration of the specific component is when the following C _P,

In any one of (1) to (4), the semipermeable membrane and the area of the semipermeable membrane constituting the first semipermeable membrane unit are determined so as to satisfy the conditions, and operating conditions are determined. Method of semi-permeable membrane device.

  (6) The method for operating a semipermeable membrane device according to any one of (1) to (5), wherein the specific component is boron.

  (7) The recovery rate in the first semipermeable membrane unit is 35% to 45%, and the recovery rate in the second semipermeable membrane unit is 80% to 90%, (1) to (6) The operation | movement method of the semipermeable membrane apparatus in any one of.

  (8) Raw water is treated with the first semipermeable membrane unit, and the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain permeated water, and the second semipermeable membrane. In the operation method of the semipermeable membrane device capable of circulating and mixing at least a part of the concentrated water of the unit with the supply water of the first semipermeable membrane unit,

If the above condition is not satisfied, the concentrated water of the second semipermeable membrane unit is not reflux mixed with the supply water of the first semipermeable membrane unit.

  (9) The operation method of the semipermeable membrane device according to any one of (4) to (8), wherein the TDS concentration of the raw water is 4% by weight or more and the boron concentration is 5 mg / l or more.

  (10) Raw water is treated with the first semipermeable membrane unit, and the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain permeated water, and the second semipermeable membrane. A semipermeable membrane device capable of recirculating and mixing at least a portion of the concentrated water of the unit with the supply water of the first semipermeable membrane unit, wherein a specific component concentration of the concentrated water of the second semipermeable membrane unit is While having a mechanism that can change the blocking rate of the first semipermeable membrane unit and the second semipermeable membrane unit so as to have a lower concentration than the raw water,

The semipermeable membrane device has a mechanism that prevents the concentrated water of the second semipermeable membrane unit from being reflux mixed with the supply water of the first semipermeable membrane unit when the condition is not satisfied.

(11) The raw water is treated with the first semipermeable membrane unit, the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain the permeated water, and the second semipermeable membrane. A semipermeable membrane device capable of refluxing and mixing at least a part of the concentrated water of the unit with the supply water of the first semipermeable membrane unit, wherein the first semipermeable membrane unit has a total salt concentration of 3.5. Pure water permeability coefficient is 3.0 × 10 ⁻¹² m ³ / m ² · Pa · s or more when simulated seawater of weight%, pH 7.0, temperature 25 ° C. is permeated at a pressure of 5.5 MPa, boron permeability coefficient A semipermeable membrane device using a semipermeable membrane of 400 × 10 ⁻⁹ m / s or less.

  According to the present invention, high quality permeated water from raw water, in particular, fresh water suitable for drinking with reduced boron concentration from seawater can be efficiently obtained.

  An example of a semipermeable membrane device to which the present invention is applicable is shown in FIG. The semipermeable membrane device shown in FIG. 1 includes a pretreatment means 2 such as a filter for pretreating seawater 1, a first semipermeable membrane unit 5 for treating pretreated water, and a first semipermeable membrane unit 5. Intermediate water tank 7 that temporarily stores the permeated water (primary permeated water 6), and a second semipermeable membrane unit 12 that processes the primary permeated water 6 stored in the intermediate water tank 7. In front of the first semipermeable membrane unit 5 and the second semipermeable membrane unit 12, a high pressure pump 4 and a booster pump 11 are provided for increasing the pressure of the supplied water. In addition, a first alkali addition means 3 for increasing the pH of the water supplied to the first semipermeable membrane unit 5 is provided in the preceding stage of the first semipermeable membrane unit 5. The second stage of the semipermeable membrane unit 12 is provided with a second alkali addition means 10 for further raising the pH of the primary permeate 6 before supplying it to the second semipermeable membrane unit 12. An acid addition means 14 for lowering the pH of the permeated water (secondary permeated water 13) of the second semipermeable membrane unit 12 is provided at the subsequent stage of the permeable membrane unit 12. Further, on the concentrated water (primary concentrated water 8) side of the first semipermeable membrane unit 5, energy recovery means 9 for recovering energy held by the primary concentrated water 8 is provided. In such a semipermeable membrane device, the pH of the seawater 1 is increased as it is or after being pretreated by the pretreatment means 2 depending on its turbidity or the like, depending on circumstances. Then, it is supplied to the first semipermeable membrane unit 5 through the high-pressure pump 4. In the first semipermeable membrane unit 5, most of the solute in the seawater can be removed, and the primary permeated water 6 from which the solute has been removed is temporarily stored in the intermediate water tank 7. On the other hand, the concentrated water (primary concentrated water 8) of the first semipermeable membrane unit 5 is discharged into the sea after the pressure energy is recovered by the energy recovery means 9.

  Subsequently, the pH of the primary permeated water 6 stored in the intermediate tank 7 is raised again by the second alkali addition means 10 in some cases, and is higher than the pH of the water supplied to the first semipermeable membrane unit 5. After being raised, the pressure is raised by the booster pump 11 and supplied to the second semipermeable membrane unit 12. In the second semipermeable membrane unit 12, the solute is further removed and the secondary permeated water 13 having a high water quality can be obtained. The secondary permeated water 13 is obtained as product water 15 after the pH is lowered by the acid addition means 14.

On the other hand, the concentrated water (secondary concentrated water 16) of the second semipermeable membrane unit 12 can be discharged into the sea as it is, but in the second semipermeable membrane unit, the primary permeated water is raw water (treated water). Therefore, turbidity and the like are sufficiently removed, and the total solute concentration is sufficiently lower than seawater, and the pH is sufficiently high, so that alkali is added as supply water to the first semipermeable membrane unit 5 Reflux before means 3. As a result, the total solute concentration of water supplied to the first semipermeable membrane unit 5 can be reduced and the pH can be raised, so that the load of osmotic pressure in the first semipermeable membrane unit 5 is reduced. In addition, the amount of alkali added in the alkali adding means 3 can be reduced. Although the valve 18 is normally closed, in the unlikely event that concentrated water having a high concentration that is not suitable for reflux flows, the valve 18 is opened and the valve 17 is closed to prevent the quality of the product water from deteriorating.
The specific component concentration of the concentrated water of the second semipermeable membrane unit aimed at in the present invention and the method of making the concentration lower than seawater or salt water pretreated with seawater include the permeated water of the first semipermeable membrane unit 5. The concentration of the second semipermeable membrane unit can be reduced or the concentration of the second semipermeable membrane unit can be reduced. More specifically, the recovery rate of the first semipermeable membrane unit 5 (ratio of the amount of permeated water to the amount of raw water) , Increase the recovery rate of the second semipermeable membrane unit 12 (ratio of the amount of permeated water to the amount of raw water), increase the raw water flow rate in the first semipermeable membrane unit, or the first semipermeable membrane unit 5 And changing the raw water pH of the second semipermeable membrane unit 12 may be performed alone or in combination. Moreover, although it is not very advantageous in terms of energy, the second aspect which is the gist of the present invention can be achieved by lowering the temperature in the first semipermeable membrane unit 5 or raising the temperature in the second semipermeable membrane unit 12. The specific component concentration of the concentrated water of the semipermeable membrane unit and the seawater or the saltwater pretreated with the seawater can be set to a lower concentration.

As a condition setting for controlling the specific component concentration of the concentrated water of the second semipermeable membrane unit and the concentration to be lower than that of seawater or saltwater pretreated with seawater, the present inventors have intensively studied, as a result of the following formula ( I found out that I should satisfy 1).
(1):

In addition,
R ₁ = recovery rate in the first semipermeable membrane unit [= permeate flow rate / raw water flow rate]
R ₂ = recovery rate in the second semipermeable membrane unit r ₁ = rejection rate in the first semipermeable membrane unit [= 1-2 × C _p / (C _f + C _b )]
r ₂ = reception rate in the second semipermeable membrane unit C _p = permeated water concentration C _f = raw water concentration C _b = concentrated water concentration.

Here, the specific control method is not particularly limited, but the operating condition of the first semipermeable membrane unit is almost determined based on the energy efficiency in consideration of the osmotic pressure of raw water, It is preferable to set the recovery rate R ₂ and the rejection rate r ₂ of the second semipermeable membrane unit based on the recovery rate R ₁ and the rejection rate r ₁ of the first semipermeable membrane unit set here. However, even if this condition is satisfied and the concentration of the specific component of the concentrated water of the second semipermeable membrane unit can be controlled to be lower than that of the raw water, the permeated water (product water) of the second semipermeable membrane unit can be controlled. If the concentration does not satisfy the required water quality, it cannot be said that sufficient performance as an apparatus is exhibited. Also in this regard, when the present inventors examined,
(2):

If r ₂ is set so as to satisfy, the object of the present invention can be achieved while satisfying the quality of the produced water, which is very preferable.

The raw water suitable for the present invention is not particularly limited to seawater, brine, river water, groundwater, drainage and treated water, but raw water containing high-concentration salinity such as seawater or seawater treated water. Application to is preferable.
In the present invention, it is desirable to increase the recovery rate (ratio of the permeated water amount to the supplied water amount) in each semipermeable membrane unit as much as possible. However, on the other hand, the higher the recovery rate, the higher the concentration of the feed water and the higher the membrane surface osmotic pressure. As a result, energy loss increases and solute precipitation occurs due to the concentration limit. Therefore, in the case of seawater with a total salt concentration of 4 to 5% by weight, the limit of the recovery rate is about 50%, and considering energy efficiency etc., it is not preferable to make it 45% or more, but if the recovery rate is lowered, it is concentrated This is also not preferable because of the increased drainage of water. Therefore, in the present invention, the recovery rate in the first semipermeable membrane unit 5 is preferably 35% or more and 45% or less. In particular, when the seawater temperature is 25 ° C. or higher, there is no problem even with a recovery rate of 45%. However, when the temperature is low, the recovery rate is lowered to around 35% according to membrane aging or changes in membrane permeability due to fouling. May be preferred and can vary depending on the situation. Subsequently, in the second semipermeable membrane unit 12, the total salt concentration is considerably reduced, so the problem of osmotic pressure due to concentration is smaller than that of the first semipermeable membrane unit 5. Since it is processed by the membrane unit 5, that is, cost is high, it is preferable to collect as much as possible. Therefore, eventually, precipitation of scale due to high concentration becomes a problem. This is greatly affected by the quality of the permeated water of the first semipermeable membrane unit and the pH due to the alkali addition in front of the second semipermeable membrane unit, but when the recovery rate is increased, the supply water flow rate decreases, Since the concentration polarization also increases, the scale is liable to precipitate, which is not preferable. Therefore, in view of these, in the second semipermeable membrane unit, it is preferable to be 80% or more and 90% or less.

  In general, the recovery rate is generally adjusted by controlling the concentrated water valve or the pump pressure. However, as disclosed in Japanese Patent Laid-Open No. 2000-093751, it is possible to control the pressure applied to the semipermeable membrane by adjusting the recovery rate by providing a back pressure by providing a valve on the permeate side. is there.

  The pretreatment means 2 may be installed according to the quality of the seawater supplied to the first semipermeable membrane unit 5 as necessary, such as sand filtration, microfiltration membrane, ultrafiltration membrane, activated carbon adsorption tower, chelate An agent addition means, an ion exchange resin tower, etc. can be used.

  It does not specifically limit as the 1st alkali addition means 3 and the 2nd alkali addition means 10, A general chemical injection pump can be used. Sodium hydroxide is generally used as the alkali to be added, but potassium hydroxide, sodium bicarbonate, ammonium hydroxide and the like can also be used. Although not shown, it is also preferable to prevent scale deposition at the addition port by providing an in-line mixer immediately after the alkali addition means 3 or by directly contacting the alkali addition port with the flow of seawater. Of course, it is also preferable to add a scale inhibitor to the seawater before adding the alkali.

  The scale inhibitor is a compound that forms a complex with a metal, metal ion, or the like in a solution and solubilizes the metal or metal salt, and an organic or inorganic ionic polymer or monomer can be used. As organic polymers, synthetic polymers such as polyacrylic acid, sulfonated polystyrene, polyacrylamide, and polyallylamine, and natural polymers such as carboxymethylcellulose, chitosan, and alginic acid can be used, and ethylenediaminetetraacetic acid can be used as a monomer. Moreover, polyphosphate etc. can be used as an inorganic type scale inhibitor.

  Among these scale inhibitors, polyphosphate and ethylenediaminetetraacetic acid (EDTA) are particularly preferably used from the viewpoints of availability, ease of operation such as solubility, and cost. The polyphosphate refers to a polymerized inorganic phosphate material having two or more phosphorus atoms in a molecule typified by sodium hexametaphosphate and bonded with an alkali metal, an alkaline earth metal and a phosphate atom. Typical polyphosphates include tetrasodium pyrophosphate, disodium pyrophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, sodium heptapolyphosphate, sodium decapolyphosphate, sodium metaphosphate, sodium hexametaphosphate, and potassium salts thereof. Etc.

  Further, the acid addition means 14 is not particularly limited, and a general chemical injection pump can be used. As the acid to be added, carbon dioxide gas or hydrochloric acid is convenient.

  The energy recovery means 9 is not particularly limited as long as the energy recovery means 9 can recover energy typified mechanically and electrically by a turbine, a water turbine or the like, thereby reducing the energy load in the system.

  Here, with respect to pH adjustment in the alkali addition means 3 and 10, boron contained in the water supplied to the semipermeable membrane unit is removed in order to remove boron as efficiently as possible even in an environment where boron removal is difficult due to high concentration and high temperature. It is necessary to dissociate the acid as much as possible, but not to raise the pH too much to generate scale. Qualitatively, the dissociation degree of boric acid shifts to the lower pH side as the solute is contained at a higher concentration, and the boric acid dissociation degree shifts to the higher pH side as the temperature becomes higher. Therefore, as a result of intensive studies by the present inventors, in the neutral region, all the solute removal performance including the boron in the semipermeable membrane itself decreases as the temperature increases, but on the other hand, the feed water containing the solute at a high concentration In the alkaline region, it was found that the boron removal rate is less likely to decrease than other solutes. Based on these results, the present inventors conducted quantitative studies, and as a result, when processing seawater with a total salt concentration of 4 to 5% by weight and a boron concentration of 5 to 7 mg / l currently assumed in the Middle East, In the assumed temperature range of 40 ° C. or lower, it has been found preferable to adjust the pH of the water supplied to the first semipermeable membrane unit 5 to 8 or more by adjusting the pH in the first alkali addition means 3. As a result, it is possible to always achieve a boron concentration reduction in the production water which is the object of the present invention, specifically 0.5 mg / l or less. On the other hand, it was also found that the pH is preferably 9 or less in order to suppress the generation of scale.

  Further, in the second semipermeable membrane unit 12, since the total salt concentration of the raw water is low and the temperature is high, the dissociation of boric acid is shifted to the high pH side and the boron removal rate is lowered. Since the boron removal performance of the first semipermeable membrane unit 5 is improved, it is possible to sufficiently remove boron by setting the pH of the supplied water, that is, the primary permeated water 6 to 9.5 or higher. Become. The permeated water (secondary permeated water 13) of the second semipermeable membrane unit 12 is suitable for drinking by adding an acid component and adjusting the pH because the pH is shifted to the alkali side. Fresh water (product water 15) can be used.

  By the way, in the present invention, it is preferable to perform pretreatment such as removal of turbid components and sterilization according to the quality of seawater supplied to the first semipermeable membrane unit as described above. By these processes, it is possible to prevent the performance of the semipermeable membrane units 5 and 12 and the subsequent process from being deteriorated, and the processing apparatus can be stably operated over a long period of time. What is necessary is just to select a specific process suitably with the property of seawater.

  When it is necessary to remove turbidity, sand filtration, microfiltration membranes, and ultrafiltration membranes are effective. At this time, when there are many microorganisms such as bacteria and algae, it is preferable to add a bactericidal agent. Chlorine is preferably used for sterilization. For example, chlorine gas or sodium hypochlorite may be added to the raw water so as to be in the range of 1 to 5 mg / l as free chlorine. In this case, it is preferable to add as much upstream as possible with respect to the flow direction of the feed water. If the chlorine concentration is high, the semipermeable membrane is deteriorated. Therefore, the residual chlorine concentration is near the raw water inlet side of the first semipermeable membrane unit 5. It is preferable to control the amount of chlorine gas and sodium hypochlorite added based on this measured value, or to add a reducing agent such as sodium bisulfite. When bacteria, proteins, natural organic components, etc. are contained in addition to the suspended matter, it is also effective to add a flocculant such as polyaluminum chloride, sulfate band, iron (III) chloride. The agglomerated feed water is then allowed to settle with a slanted plate, etc., and then sand filtered, or filtered with a microfiltration membrane or an ultrafiltration membrane in which a plurality of hollow fiber membranes are bundled. Supply water suitable for passing through the semipermeable membrane can be obtained. In particular, when adding the flocculant, it is preferable to adjust the pH so that the flocculent is easy to flocculate, and the pH is generally 5 or more and less than 8, and preferably 7 or less. In the present invention, when the pH is lowered in the addition of the flocculant, the boron removal rate decreases unless the pH is raised before the first semipermeable membrane. It is very important to add an alkali to ensure that the pH is 8 or more.

  On the other hand, when seawater contains a lot of soluble organic substances, these organic substances can be decomposed by adding chlorine gas or sodium hypochlorite, but they can also be removed by activated carbon filtration. . In addition, when a large amount of soluble inorganic substance is contained, a chelating agent such as an organic polymer electrolyte or sodium hexametaphosphate may be added, or exchanged with soluble ions using an ion exchange resin or the like. Further, when iron or manganese is present in a soluble state, it is preferable to use an aeration oxidation filtration method or a contact oxidation filtration method.

  The high-pressure pump 4 is not particularly limited and can be appropriately selected and used according to the required output. However, in the present invention, it is necessary to apply a pressure higher than the osmotic pressure to the supply water. The pressure of 3 MPa is indispensable, and it is necessary to output a pressure of 5 MPa or more at a necessary flow rate. The booster pump 11 is not particularly limited, but is for supplying the permeated water of the first semipermeable membrane unit, and it is not necessary to consider the osmotic pressure. And low pressure and low flow rate. The specific pressure is preferably one at which a maximum pressure of 2 MPa can be applied.

However, if a pressure significantly higher than the osmotic pressure of the supplied raw water 1 is applied, the permeation flux at the inlet portion of the first semipermeable membrane is too large, and organic substances and the like present in a minute amount in the raw water are present on the membrane surface. It is not preferable because the film is deposited and adsorbed to deteriorate the film performance. Therefore, specifically, the local permeation flux at the inlet of the first semipermeable membrane unit 5 is 1.0 m ³ / m ² · day or less, preferably 0.5 m ³ / m ² · day or less. It is preferable to apply pressure.

By the way, the specific component according to the present invention can be exemplified by boron, bromine, calcium, magnesium and the like, but is not particularly limited. Among these, when the present invention is applied to boron, which is the biggest problem when drinking water is obtained from seawater, the effect is large and preferable.
The first semipermeable membrane unit 5 and the second semipermeable membrane unit 12 use a fluid separation element (element) in which a hollow fiber membrane or a flat membrane is housed in a housing for easy handling. When the fluid separation element is formed of a flat membrane, for example, as shown in FIG. 5, a semipermeable membrane 30 and a permeate flow channel such as a tricot are formed around a cylindrical central pipe 29 having a large number of holes. It is preferable that a membrane unit including a material 32 and a supply water flow path material 31 such as a plastic net is wound, and these are housed in a cylindrical casing. It is also preferable to form a separation membrane module by connecting a plurality of fluid separation elements in series or in parallel. In this fluid separation element, the supply water 25 is supplied into the unit from one end, and the permeated water 27 that has permeated through the semipermeable membrane 30 before reaching the other end is supplied to the central pipe 30. The flow is withdrawn from the central pipe 29 at the other end. On the other hand, the supply water 25 that has not permeated the semipermeable membrane 30 is taken out as concentrated water 26 at the other end.

  As the material of the semipermeable membrane 30, polymer materials such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer can be used. In addition, the membrane structure has a dense layer on at least one side of the membrane, and on the asymmetric membrane having fine pores gradually increasing from the dense layer to the inside of the membrane or the other side, or on the dense layer of the asymmetric membrane. Either a composite film having a very thin functional layer formed of another material may be used.

  However, among them, a composite membrane having a functional layer of polyamide having high pressure resistance, high water permeability, and high solute removal performance and having an excellent potential is preferable. In particular, in the case of the first semipermeable membrane unit, in order to obtain fresh water from seawater, it is necessary to apply a pressure equal to or higher than the osmotic pressure, and an operating pressure of at least 5 MPa is substantially required. In order to maintain high water permeability and blocking performance against this pressure, a structure in which polyamide is used as a functional layer and is held by a support made of a porous membrane or nonwoven fabric is suitable. As the polyamide semipermeable membrane, a composite semipermeable membrane having a functional layer of a crosslinked polyamide obtained by polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide on a support is suitable.

  The separation functional layer is preferably made of a cross-linked polyamide having high chemical stability with respect to acid or alkali, or made of a cross-linked polyamide as a main component. The crosslinked polyamide is preferably formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide, and at least one of the polyfunctional amine or the polyfunctional acid halide component preferably contains a trifunctional or higher functional compound.

  Here, the polyfunctional amine refers to an amine having at least two primary and / or secondary amino groups in one molecule. For example, two amino groups are any of ortho, meta, and para positions. Aromatic polyfunctional amines such as phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene and 3,5-diaminobenzoic acid bonded to benzene in the positional relationship of Aliphatic amines such as ethylenediamine and propylenediamine, alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 1,3-bispiperidylpropane and 4-aminomethylpiperazine be able to. Of these, aromatic polyfunctional amines are preferred in view of selective separation, permeability, and heat resistance of the membrane. Examples of such polyfunctional aromatic amines include m-phenylenediamine, p-phenylenediamine, 1, 3,5-triaminobenzene is preferably used. Furthermore, it is more preferable to use m-phenylenediamine (hereinafter referred to as m-PDA) from the standpoint of availability and ease of handling. These polyfunctional amines may be used alone or in combination.

  The polyfunctional acid halide refers to an acid halide having at least two carbonyl halide groups in one molecule. Examples of trifunctional acid halides include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, 1,2,4-cyclobutanetricarboxylic acid trichloride, and bifunctional acid halides include biphenyl dicarboxylic acid. Aromatic difunctional acid halides such as acid dichloride, biphenylene carboxylic acid dichloride, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalene dicarboxylic acid chloride, aliphatic difunctional acid such as adipoyl chloride, sebacoyl chloride Mention may be made of alicyclic bifunctional acid halides such as halides, cyclopentane dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, tetrahydrofuran dicarboxylic acid dichloride. Considering the reactivity with the polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional acid chloride, and considering the selective separation property and heat resistance of the membrane, the polyfunctional aromatic acid chloride is preferable. Preferably there is. Among them, it is more preferable to use trimesic acid chloride from the viewpoint of easy availability and easy handling. These polyfunctional acid halides may be used alone or in combination.

In the present invention, it is desirable that the semipermeable membrane used in the first semipermeable membrane unit 5 can highly remove solutes such as ions in seawater. In particular, boron having a low rejection rate compared to other components preferably has a high rejection performance. Specifically, as the semipermeable membrane of the first semipermeable membrane unit 5, pure seawater when a simulated seawater having a total salt concentration of 3.5% by weight, pH 7.0, and temperature of 25 ° C. is supplied at an operating pressure of 5.5 MPa. By applying a material having a water permeability coefficient of 3 × 10 ⁻¹² m ³ / m ² · Pa · s or more and a boron permeability coefficient of 400 × 10 ⁻⁹ m / s or less, which can express the performance. While realizing the operation control of the invention, high quality fresh water can be obtained.

Here, the simulated seawater having a total salt concentration of 3.5% by weight is NaCl = 2.926 g / l, Na ₂ SO ₄ = 4.006 g / l, KCl = 0.538 g / l, NaHCO ₃ = 0.196 g. / L, MgCl ₂ = 5.072 g / l, CaCl ₂ = 1.147 g / l, and H ₃ BO ₃ = 0.0286 g / l.

The pure water permeability coefficient L _p and the boron permeability coefficient P _b can be obtained by the following method in consideration of the concentration polarization phenomenon occurring on the film surface. For example, in the case of measuring with a flat membrane, a flat membrane cell shown in Reference 1 (J. M. Taniguchi et al., Journal of Membrane Science, Vol. 183, 2000, p259-267), etc. Measure the permeation flux and blocking performance of the simulated seawater, and calculate L _p and P _b by the following equations.
J _v = L _p (ΔP−Δπ)
J _s = P (C _m −C _p )
J _sb = P _b (C _mb −C _pb )
Δπ = π (C _m ) −π (C _p )
_{(C m -C p) / (} C f -C p) = exp (J v / k)
_{(C mb -C p) / (} C fb -C pb) = exp (J v / k b)
J _v : pure water permeation flux [m ³ / m ² · s]
J _s : TDS permeation flux [kg / m ² · s]
J _sb : Boron permeation flux [kg / m ² · s]
L _p : Pure water permeability coefficient [m ³ / m ² · Pa · s]
P: TDS transmission coefficient [m / s]
P _b : Boron permeability coefficient [m / s]
π (): TDS osmotic pressure [Pa]
Δπ: Osmotic pressure difference [Pa]
ΔP: Operating pressure difference [Pa]
C _m : TDS raw water film surface concentration [kg / m ³ ]
C _f : TDS raw water bulk concentration [kg / m ³ ]
C _p : TDS permeated water concentration “kg / m ³ ”
C _mb : Boron raw water film surface concentration [kg / m ³ ]
C _fb : Boron raw water bulk concentration [kg / m ³ ]
C _pb : Boron permeated water concentration “kg / m ³ ”
k: TDS mass transfer coefficient [m / s]
k _b : Boron mass transfer coefficient [m / s].

Here, the osmotic pressure π is determined by the so-called “Miyake's formula” shown in Reference 1 and Reference 2 (AIChE Journal by M. Taniguchi et al., Vol. 46, 2000, p1967-1973). I can know. The TDS mass transfer coefficient k is a value determined by the evaluation cell, but the membrane surface flow rate Q [m ³ / s] or the membrane surface flow velocity u [m / m] is determined by the osmotic pressure method or the flow velocity change method shown in Reference Document 2. s] as a function.

In the case of the flat membrane cell shown in Reference 1,
k = 1.63 × 10 ⁻³ · Q ^0.4053
It is. Subsequently, as is a boron mass-transfer coefficient k _b, which is also shown in the literature,
k / k _b = (D / D _b ) ^0.75
D: TDS diffusion coefficient [m ² / s]
D _b : Boron diffusion coefficient [m ² / s]
It can be calculated from

Therefore, the unknowns L _p , P, P _b , C _m , and C _mb can be calculated from the above formula. In the case of a membrane element, as shown in Reference Document 2, L _p and P can be calculated by fitting while integrating in the length direction of the membrane element.

  In order to obtain such a composite semipermeable membrane suitable for the first semipermeable membrane in the present invention and capable of obtaining such a high boron-blocking performance, for example, a method in which an aliphatic acyl group is present inside or on the surface may be mentioned. For example, a separation functional layer having a separation performance of ions or the like is provided on a microporous support membrane having substantially no separation performance, and an aliphatic acyl group is provided inside and / or on the surface of the separation function layer. To exist. The aliphatic acyl group may be present in the separation functional layer or on the surface of the separation functional layer by bonding.

  The method for causing the aliphatic acyl group to be present in the separation functional layer is not particularly limited. For example, the aliphatic acid group is formed on the surface of the separation functional layer formed by interfacial polycondensation between a polyfunctional amine and a polyfunctional acid halide. If the aliphatic acid halide is allowed to coexist in the separation functional layer by contacting the halide solution or coexisting the aliphatic acid halide during the interfacial polycondensation between the polyfunctional amine and the polyfunctional aromatic acid halide, Good.

  That is, in forming the polyamide separation functional layer on the microporous support membrane, the polyamide separation functional layer is composed of a polyfunctional amine aqueous solution, a polyfunctional acid halide organic solvent solution, and a carbon number different from this. Or an organic solvent solution of an aliphatic acid halide within the range of ˜4 on a microporous support membrane and interfacial polycondensation. A functional acid halide and an organic solvent solution containing an aliphatic acid halide having a different carbon number in the range from 1 to 4 are brought into contact with each other on a microporous support membrane and subjected to interfacial polycondensation. That's fine.

  In that case, the aliphatic acid halide used in the present invention usually has 1 to 4 carbon atoms, but preferably 2 to 4 carbon atoms. As the number of carbon atoms increases, the reactivity of the aliphatic acid halide decreases due to steric hindrance, and the access to the reaction point of the polyfunctional acid halide becomes difficult, thereby preventing smooth film formation. The performance of is reduced.

  Examples of the aliphatic acid halide include methanesulfonyl chloride, acetyl chloride, propionyl chloride, butyryl chloride, oxalyl chloride, malonic acid dichloride, succinic acid dichloride, maleic acid dichloride, fumaric acid dichloride, chlorosulfonylacetyl chloride, N, N -Dimethylaminocarbonyl chloride etc. are mentioned. These may be used alone or in combination of two or more. However, it is preferable that oxalyl chloride is a main component as a balanced structure that can form a dense structure and does not significantly reduce water permeability.

  The support including the microporous support membrane is a layer that does not substantially have separation performance, and is provided to give mechanical strength to the separation functional layer of the crosslinked polyamide having substantial separation performance. For example, a material in which a microporous support film is formed on a substrate such as a fabric or a nonwoven fabric is used.

  Moreover, as a support body used for a semipermeable membrane, the polysulfone microporous support membrane reinforced with the cloth can be illustrated. A microporous support membrane is a layer that has substantially no separation performance and is used to give mechanical strength to a functional layer that has substantially separation performance. It is preferable that the support film has a structure in which the fine pores gradually increase from one surface to the other surface, and the size of the fine pores is 100 nm or less on one surface. The microporous support membrane can be selected from various commercially available materials such as “Millipore Filter VSWP” (trade name) manufactured by Millipore and “Ultra Filter UK10” (trade name) manufactured by Toyo Roshi Kaisha, Usually, “Office of Saleen Water Research and Development Progress Report” No. 359 (1968). Polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride and other homopolymers or blends are usually used as the material. Polysulfone, which has high chemical, mechanical and thermal stability, is used. It is preferred to use. For example, a dimethylformamide (DMF) solution of the above polysulfone is cast on a densely woven polyester cloth or non-woven fabric to a certain thickness, and this is poured into an aqueous solution containing 0.5% by weight of sodium dodecyl sulfate and 2% by weight of DMF. By wet coagulation with, a microporous support membrane having a fine pore having a diameter of several tens of nm or less on the surface is obtained. As a material for the microporous support membrane, polyamide and polyester are preferably used in addition to polysulfone.

  The present invention can be further modified by an apparatus as shown in FIGS. However, the present invention is not limited to these embodiments.

  FIG. 2 shows an example of an apparatus in which the energy recovered by the energy recovery means 9 is utilized for the energy of the booster pump of the supply water. The energy recovery means 9 and the booster pump 11 in FIG. 1 are integrated. With this configuration, the permeated water of the first semipermeable membrane unit 5 can be boosted without power and supplied to the second semipermeable membrane unit 12, so that the recovered energy can be utilized without surplus. Other flows are the same as those in the apparatus shown in FIG. Although not shown, in the present invention, since the pressure energy of the concentrated water of the final semipermeable membrane unit is the largest, it is preferable to recover and reuse this energy.

  FIG. 3 shows a second semipermeable membrane in which the second semipermeable membrane unit is configured in two banks, and the concentrated water (first bank concentrated water 16) is processed after the second semipermeable membrane unit first bank 12. A membrane unit second bank 21 is provided. Here, by changing the configuration of the semipermeable membrane of the first bank and the second bank, it is possible to efficiently perform the processing in the second bank having a higher concentration. However, even in such a configuration, when the pH of the water supplied to the second semipermeable membrane unit is 9.5 or more and the recovery rate is 90% (that is, the concentration rate is about 10 times) or more, Therefore, the recovery rate is preferably 90% or less in the second semipermeable membrane unit. Furthermore, from the viewpoint of reliably preventing scale deposition, it is preferable to set the recovery rate of the second semipermeable membrane unit to 85% or less. As a result, the overall recovery rate of the present apparatus can be 30 to 40%. 3 is the same as that of the apparatus of FIG.

  FIG. 4 shows a configuration in which a back pressure valve 24 is provided in the permeate 6 of the first semipermeable membrane unit 5. In general, the recovery rate is generally adjusted by controlling the concentrated water valve and the pump pressure, but with this configuration, the first semipermeable membrane can be obtained without changing the output of the high-pressure pump 4. The pressure acting on 5 can be adjusted. Furthermore, it is also preferable to apply a back pressure to the permeated water of the second semipermeable membrane unit or the third semipermeable membrane unit. The other flows in FIG. 4 are the same as those in the apparatus in FIG.

The total salt concentration in the permeated water and the supply water is determined by measuring the electrical conductivity of each solution with an electrical conductivity meter (SC82 manufactured by Yokogawa Electric Corporation). Asked. In addition, the boron concentration and the cation (Na ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ ) concentration in the feed water and permeated water are measured with an ICP emission analyzer (P-4010 manufactured by Hitachi, Ltd.), and anions (Cl ⁻ , SO ₄ ²⁻ ) concentration was measured with an ion chromatograph (DX-210 manufactured by Nippon Dionex). The pH was measured using a PH82 manufactured by Yokogawa Electric.

  The fiber-reinforced polysulfone support (ultrafiltration membrane) used in the examples was produced by the following method.

Wet non-woven fabric (mixed fibers with monofilaments of 0.5 and 1.5 dtex, air permeability of 0.7 cm ³ / cm ² · s, average pore diameter of 7 μm or less) made of polyester fiber having a size of vertical 30 cm and horizontal 20 cm Immediately cast a 15% by weight dimethylformamide (DMF) solution of polysulfone (Udel (registered trademark) -P3500 manufactured by Union Carbide Co.) at a thickness of 200 μm at room temperature (20 ° C.), and immediately A fiber-reinforced polysulfone support (hereinafter abbreviated as FR-PS support) was prepared by immersing in pure water at room temperature and allowing to stand for 5 minutes. The permeation flux of the obtained FR-PS support (thickness 210 to 215 μm) was 1.7 m ³ / m ² · day as measured at a pressure of 0.1 MPa and a temperature of 25 ° C.

  The FR-PS support thus obtained was immersed in a 3.4% by weight aqueous solution of m-phenylenediamine for 2 minutes, the support was slowly pulled up in the vertical direction, and nitrogen was blown from an air nozzle to form a support film. Excess aqueous solution was removed from the surface. Thereafter, an n-decane mixed solution of polyfunctional aromatic acid halide and aliphatic acid halide prepared with a composition of 0.15% by weight of trimesic acid chloride and 0.030% by weight of oxalyl chloride was completely wetted on the surface. Then, the membrane was left to stand for 1 minute, and then the membrane was held vertically for 1 minute to drain the liquid. Subsequently, the decane solvent was evaporated by air drying, and the remaining chemical solution in the membrane was washed with running water with tap water. Thereafter, it was washed with hot water at 90 ° C. for 2 minutes, immersed in a 200 mg / l sodium hypochlorite aqueous solution adjusted to pH 7 for 2 minutes, and then immersed in a 1,000 mg / l sodium hydrogen sulfite aqueous solution. Furthermore, this membrane was rewashed with hot water at 95 ° C. for 2 minutes.

This composite semipermeable membrane was formed using a flat membrane cell shown in Journal of Membrane Science, Vol. 183, 2000, p259-267 by M. Taniguchi et al. Evaluation was made at a flow rate of 3.5 l / min using simulated seawater (boron concentration 4.5 mg / l) with a supply pressure of 5.5 MPa, 25 ° C., pH 7.0, and a total solute concentration of 3.5 wt%. The flux was 0.67 m ³ / m ² · day, the permeated water TDS concentration was 63 ppm, and the permeated water boron concentration was 0.28 mg / l. The composite semipermeable membrane has a pure water permeability coefficient Lp = 3.69 × 10 ⁻¹² m ³ / m ² · Pa · s, a boron permeability coefficient Pb = 368 × 10 ⁻⁹ m / s, and the pure water permeability coefficient is It became a semipermeable membrane suitable for seawater desalination having a large boron permeability coefficient (this membrane is referred to as UTC-A).

Moreover, when the flat membrane used in the Toray Industries, Inc. SU-810 membrane element was similarly evaluated,
g / l. This composite semipermeable membrane has a pure water permeability coefficient Lp = 4.02 × 10 ⁻¹² m ³ / m ² · Pa · s and a boron permeability coefficient Pb = 543 × 10 ⁻⁹ m / s, which is higher than that of UTC-A. In addition, large values were obtained for both the pure water permeability coefficient and the boron permeability coefficient.

Subsequently, a membrane element (diameter 10 cm, total length 1 m) shown in FIG. 5 was produced using the obtained membrane (UTC-A). (Hereinafter, this membrane element is referred to as SU-A.)
Subsequently, a flow evaluation apparatus (hereinafter referred to as apparatus A) shown in FIG. 6 was constructed.

  The apparatus A includes a raw water tank 33, a high pressure pump 4, a first semipermeable membrane unit 5, a booster pump 11, a second semipermeable membrane unit 12, a second semipermeable membrane unit (second bank) 21, and the like. The output of the high-pressure pump 4 is controlled by an inverter, and the output of the booster pump 11 is not regulated, but is substantially controlled by the pressure regulating valve 40. The flow rate of the permeated water 6 of the first semipermeable membrane unit 5 can be adjusted by the first semipermeable membrane unit concentrated water valve 19, and the flow rate of the permeated water of the second semipermeable membrane unit can be adjusted by the pressure regulating valve. 40 and the back pressure valve 42 can be adjusted. The first semipermeable membrane unit 5 has a diameter of 10 cm and six membrane elements each having a total length of 1 m, connected in series, two in parallel, and the second semipermeable membrane unit (first bank) 12 has a diameter of 10 cm. , Two parallel 1m membrane elements connected in series, 2 parallel, second semipermeable membrane unit (second bank) 21 having two 10m diameter, 1m total membrane elements connected in series 1 It is structured as a column.

<Comparative Example 1>
Using apparatus A, pretreatment of seawater in the vicinity of Toray Industries, Inc. Ehime Factory to remove turbidity, and then concentrating through 6 units of Toray Industries, Inc. SU-820 connected in series, 40 A salt solution with a total solute concentration of 4.5% by weight (boron concentration of 5.4 mg / l), heated to ℃ and adjusted to pH 8.0, was used as the first membrane element for a semipermeable membrane unit at a flow rate of 60 m ³ / day. Using Toray Industries, Inc. SU-810 and Toray Industries, Inc. SU-710 as the membrane element for the second semipermeable membrane unit, the recovery rate of the first semipermeable membrane unit is 40%, and the second semipermeable membrane is used. The unit was operated at a recovery rate of 85% and a flow rate of the permeated water 22 of 21.7 m ³ / day. At this time, the pH was adjusted by the second alkali addition means 10 so that the permeated water boron concentration was 1 mg / l while measuring the permeated water boron concentration. The boron concentration in the concentrated water (refluxed water) of the second semipermeable membrane unit after 1 hour operation was 7.3 mg / l, which was higher than the raw water concentration 5.4 mg / l, and was not suitable for refluxing. At this time, r ₁ = 71.1%, r ₂ = 78.4%, and the formula (1) was not satisfied. Further, when the target permeated water boron concentration C _p = 1 mg / l, the expression (2) was satisfied, but when C _p = 0.5 mg / l, the expression (2) was not satisfied. The total salt concentration of the permeated water 22 was 54 ppm, and the pH of the raw water 6 of the second semipermeable membrane unit was 9.6.

<Example 1>
The same configuration and conditions as in Comparative Example 1 except that the recovery rate of the first semipermeable membrane unit is 43%, the recovery rate of the second semipermeable membrane unit is 75%, and the flow rate of the permeated water 22 is 21.7 m ³ / day. As a result, the boron concentration of the concentrated water (refluxed water) of the second semipermeable membrane unit was 4.1 mg / l, which was smaller than the raw water concentration of 5.4 mg / l, and was suitable for refluxing. At this time, r ₁ = 73.1% and r ₂ = 65.9% satisfied the expression (1). Further, when the target permeated water boron concentration C _p = 1 mg / l, the expression (2) was satisfied, but when C _p = 0.5 mg / l, the expression (2) was not satisfied. The total salt concentration of the permeated water 22 was 27 ppm, and the pH of the raw water 6 of the second semipermeable membrane unit was 9.3.

<Example 2>
Except for using SU-A as the membrane element for the first semipermeable membrane unit, the same concentration as in Comparative Example 1 was operated under the same conditions. As a result, the boron concentration in the concentrated water (refluxed water) of the second semipermeable membrane unit was The concentration was 4.0 mg / l, which was smaller than the raw water concentration of 5.4 mg / l, and was suitable for reflux. At this time, r ₁ = 78.1% and r ₂ = 63.4% were satisfied, and the formula (1) was satisfied. Further, when the target permeated water boron concentration C _p = 1 mg / l, the expression (2) was satisfied, but when C _p = 0.5 mg / l, the expression (2) was not satisfied. The total salt concentration of the permeated water 22 was 59 ppm, and the pH of the raw water 6 of the second semipermeable membrane unit was 9.2.

<Comparative example 2>
The concentrated water of the second semipermeable membrane unit was obtained as a result of operation under the same configuration and conditions as in Example 2 except that the pH was adjusted by the second alkaline means 10 so that the boron concentration of the permeated water was 0.5 mg / l. The boron concentration of (refluxed water) was 7.2 mg / l, which was higher than the raw water concentration of 5.4 mg / l and was not suitable for refluxing. At this time, r ₁ = 79.3% and r ₂ = 88.5%, and the expression (1) was not satisfied. Further, the formula (2) was satisfied when the target permeated water boron concentration C _p = 1 mg / l and C _p = 0.5 mg / l. The total salt concentration of the permeated water 22 was 84 ppm, and the pH of the raw water 6 of the second semipermeable membrane unit was 10.0.

<Example 3>
The same configuration and the same conditions as Comparative Example 2 except that the recovery rate of the first semipermeable membrane unit is 43%, the recovery rate of the second semipermeable membrane unit is 75%, and the flow rate of the permeated water 22 is 21.7 m ³ / day. As a result, the concentration of boron in the concentrated water (refluxed water) of the second semipermeable membrane unit was 3.9 mg / l, which was smaller than the raw water concentration of 5.4 mg / l, and was suitable for refluxing. At this time, r ₁ = 79.9% and r ₂ = 88.1% were satisfied with the expression (1). Further, the formula (2) was satisfied both when the target permeated water boron concentration C _p = 1 mg / l and when C _p = 0.5 mg / l. The total salt concentration of the permeated water 22 was 44 ppm, and the pH of the raw water 6 of the second semipermeable membrane unit was 9.7.

It is a schematic flowchart which shows one embodiment of the semipermeable membrane apparatus which concerns on this invention. It is a schematic flowchart which shows the other embodiment of the semipermeable membrane apparatus which concerns on this invention. It is a schematic flowchart which shows the other embodiment of the semipermeable membrane apparatus which concerns on this invention. It is a schematic flowchart which shows the other embodiment of the semipermeable membrane apparatus which concerns on this invention. . It is an example of the semipermeable membrane element used for the semipermeable membrane apparatus which concerns on this invention. It is a flowchart of the semipermeable membrane unit evaluation apparatus used in the Example.

Explanation of symbols

1: Raw water 2: Pretreatment 3: First alkali addition means 4: High-pressure pump 5: First semipermeable membrane unit 6: Second semipermeable membrane unit raw water 7: Intermediate water tank 8: First semipermeable Membrane unit concentrated water 9: Energy recovery means 10: Second alkali addition means 11: Booster pump 12: Second semipermeable membrane unit 13: Second semipermeable membrane unit permeated water 14: Acid addition means 15: Production water Tank 16: Second semipermeable membrane unit concentrated water 17: Second semipermeable membrane unit concentrated water reflux valve 18: Second semipermeable membrane unit concentrated water drain valve 19: First semipermeable membrane unit concentrated water valve 20: First semipermeable membrane unit permeate bypass valve 21: Second semipermeable membrane unit (second bank)
22: Second semipermeable membrane unit permeated water (second bank)
23: Second semipermeable membrane unit concentrated water (second bank)
24: Back pressure valve 25: Raw water 26: Concentrated water 27: Permeated water 28: Sealing material 29: Center pipe 30: Semipermeable membrane 31: Raw water channel material 32: Permeated water channel material 33: Raw water tank 34: Raw water pressure gauge 35: Concentrated water pressure gauge 36: First permeated water pressure gauge 37: Second supply water pressure gauge 38: Second permeated water pressure gauge 39: Second concentrated water pressure gauge 40: Pressure adjustment valve 41: Bypass valve 42: Permeation Water back pressure valve

  The operation method of the semipermeable membrane device of the present invention enables the production of fresh water from which high water quality, particularly boron is highly removed.

Claims (11)

The raw water is treated with the first semipermeable membrane unit, the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain the permeated water, and the second semipermeable membrane unit. In the operation method of the semipermeable membrane device capable of refluxing and mixing at least a part of the concentrated water to the raw water of the first semipermeable membrane unit, the specific component concentration of the concentrated water of the second semipermeable membrane unit is the above-described concentration. A method for operating a semipermeable membrane device, wherein the blocking rate of specific components of the first semipermeable membrane unit and the second semipermeable membrane unit is changed so as to have a lower concentration than the raw water. The method for changing the rejection rate is by controlling the recovery rate, which is the permeate flow rate relative to the raw water flow rate, or by controlling at least one temperature, pH, or flow rate selected from raw water, permeate water, and concentrated water. The method of operating a semipermeable membrane device according to claim 1. When the recovery rate of the first semipermeable membrane unit is R ₁ , the rejection rate of the specific component is r ₁ , the recovery rate of the second semipermeable membrane unit is R ₂ , and the rejection rate of the specific component is r ₂ ,

The method for operating the semipermeable membrane device according to claim 1, wherein: The method of operating a semipermeable membrane device according to claim 1 or 2, wherein the raw water is seawater or salt water pretreated from seawater. In the operating method of the semipermeable membrane device, the raw water is treated with the first semipermeable membrane unit, and the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain the permeated water. The rejection rate of the specific component of one semipermeable membrane unit is r ₁ , the rejection rate of the specific component of the second semipermeable membrane unit is r ₂ , the raw water concentration is C _F , and the target permeated water concentration of the specific component is C _P or less And when

The semipermeable membrane constituting the first semipermeable membrane unit and the area of the semipermeable membrane are determined so as to satisfy the conditions, and the operating conditions are defined. Operation method of the permeable membrane device. The method for operating a semipermeable membrane device according to claim 1, wherein the specific component is boron. The recovery rate in the first semipermeable membrane unit is 35% or more and 45% or less, and the recovery rate in the second semipermeable membrane unit is 80% or more and 90% or less. Method of semi-permeable membrane device. Raw water is treated with the first semipermeable membrane unit, and the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain permeated water, and the second semipermeable membrane unit is concentrated. In the operation method of the semipermeable membrane device capable of circulating and mixing at least part of the water with the supply water of the first semipermeable membrane unit,

If the above condition is not satisfied, the concentrated water of the second semipermeable membrane unit is not reflux mixed with the supply water of the first semipermeable membrane unit. The operation method of the semipermeable membrane device according to any one of claims 4 to 8, wherein the TDS concentration of the raw water is 4% by weight or more and the boron concentration is 5 mg / l or more. Raw water is treated with the first semipermeable membrane unit, and the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain permeated water, and the second semipermeable membrane unit is concentrated. A semipermeable membrane device capable of circulating and mixing at least a part of water with the supply water of the first semipermeable membrane unit, wherein the concentration of the specific component of the concentrated water of the second semipermeable membrane unit is the raw water In addition to having a mechanism that can change the blocking rate of the first semipermeable membrane unit and the second semipermeable membrane unit so that the concentration is lower than

The semipermeable membrane device has a mechanism that prevents the concentrated water of the second semipermeable membrane unit from being reflux mixed with the supply water of the first semipermeable membrane unit when the condition is not satisfied. Raw water is treated with the first semipermeable membrane unit, and the permeated water from the first semipermeable membrane unit is treated with the second semipermeable membrane unit to obtain permeated water, and the second semipermeable membrane unit is concentrated. A semipermeable membrane device capable of refluxing and mixing at least part of water with the supply water of the first semipermeable membrane unit, wherein the first semipermeable membrane unit has a total salt concentration of 3.5% by weight, The pure water permeability coefficient is 3.0 × 10 ⁻¹² m ³ / m ² · Pa · s or more when simulated seawater at pH 7.0 and temperature of 25 ° C. is permeated at a pressure of 5.5 MPa, and the boron permeability coefficient is 400 ×. A semipermeable membrane device using a semipermeable membrane of 10 ⁻⁹ m / s or less.

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