JP4765843B2 - Seawater desalination method - Google Patents

Description

  The present invention relates to a desalination treatment using a reverse osmosis membrane of seawater. In particular, the present invention is effective in improving the removal rate of boron that is difficult to remove in a reverse osmosis membrane as compared with other inorganic salts.

  The reverse osmosis method is used in a wide range of fields such as desalination of seawater and brine, production of pure water for the semiconductor industry and pharmaceutical industry, ultrapure water, and municipal wastewater treatment. Compared to the evaporation method and electrodialysis method, it is advantageous in terms of energy saving and is widely spread. In particular, since the hollow fiber type reverse osmosis membrane can increase the membrane area per unit volume, the hollow fiber type reverse osmosis membrane has a shape suitable for membrane separation operation, and is widely used, for example, in the field of seawater desalination using a reverse osmosis membrane.

  Water treated by the reverse osmosis method is also used for drinking water, but with increasing safety awareness, compliance with water quality standards is required. Therefore, a two-stage method in which the permeated water of the reverse osmosis membrane is once collected and treated again with the reverse osmosis membrane has been studied. For example, in seawater desalination using a reverse osmosis membrane, the boron concentration of the permeated water may not meet the water quality standard, and a two-stage method may be applied.

Conventionally, all or part of the permeated water treated with the first-stage reverse osmosis membrane is treated with the second-stage reverse osmosis membrane, and the concentrated water of the second-stage reverse osmosis membrane is returned to the first-stage feed water. A processing method is disclosed. (See Patent Document 1). This is because the quality of the permeated water is improved by the two-stage method and the recovery rate of the entire two-stage system is increased. However, in this method, when the concentration of the concentrated water in the second-stage reverse osmosis membrane is high, the concentration of the first-stage feed water is high, and as a result, the concentration of the permeated water in the second-stage reverse osmosis membrane is high. This is not preferable. In particular, in the case of seawater desalination, in order to improve the removal performance of boron, by adding alkali to the supply water of the second-stage reverse osmosis membrane module, for example, the pH is set to 8.5 or more, and 2 When the boron removal performance of the reverse osmosis membrane module of the second stage is improved, the boron in the concentrated water of the reverse osmosis membrane module of the second stage is concentrated and differs depending on the recovery rate, but becomes higher than the boron concentration of the raw water. There is a case.
U.S. Pat. No. 4,574,049 (column 3, line 34 to column 4, line 4, FIG. 1)

Also disclosed is a two-stage method in which only the permeate of the reverse osmosis membrane element on the concentration side of the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module for the purpose of removing boron in seawater desalination. Has been. (Refer nonpatent literature 1). However, the permeated water from the first-stage reverse osmosis membrane module separates the supply side permeated water and the concentrated side permeated water outlet, but the division within the reverse osmosis membrane module is not clear, and the supply side permeate is not clear. There is a problem that the concentration of the water and the concentrated permeate cannot be controlled, and it is difficult to control the water supplied to the second stage.
New Membrane Technology Symposium 2002 Proceedings (Pages 6-1-1 to 6-1-10)

  On the other hand, all or part of the permeated water treated with the first-stage reverse osmosis membrane is treated with the second-stage reverse osmosis membrane, and the concentrated water of the second-stage reverse osmosis membrane is returned to the first-stage feed water. Furthermore, in the method of treating the permeated water of the second-stage reverse osmosis membrane module with an adsorption resin such as a chelate resin that selectively adsorbs ions, for example, boron is removed with an adsorption resin in seawater desalination. However, since the boron concentration itself is low, the boron adsorption amount per adsorbed resin amount is small and the efficiency is low. Further, impurities eluted from the adsorbent resin are mixed in the treated water, which may not be suitable for drinking water, and there is a problem that it is necessary to install activated carbon for the removal.

  The present invention has been made in view of such a point, and is a two-stage treatment with a reverse osmosis membrane, and a system for returning the concentrated water of the second-stage reverse osmosis membrane module to the first-stage supply water. In the second stage reverse osmosis membrane module is treated with an adsorption resin to suppress an increase in the solute concentration of the feed water of the first stage reverse osmosis membrane module, resulting in the second stage reverse osmosis. It is an object of the present invention to provide a treatment method capable of efficient treatment that reduces the concentration of permeated water of a membrane module and prevents contamination of permeated water by an adsorbent resin.

The inventors of the present invention have arrived at the present invention as a result of intensive studies to overcome the above problems. That is, the present invention has the following configuration.
(1) In a seawater desalination facility having a two-stage reverse osmosis membrane module, a route for returning at least a part of the concentrated water obtained from the second-stage reverse osmosis membrane module to the first-stage reverse osmosis membrane module A seawater desalination facility comprising an adsorption resin tower.
(2) The seawater desalination facility according to (1), wherein the adsorption resin has an action of selectively adsorbing and collecting an object to be removed in an aqueous solution.
(3) The seawater desalination facility according to (1) or (2), wherein the removal target is boron.
(4) The seawater desalination facility according to any one of (1) to (3), wherein the first-stage reverse osmosis membrane module is made of a hollow fiber membrane made of a cellulose acetate polymer.
(5) The seawater desalination facility according to any one of (1) to (4), wherein the second-stage reverse osmosis membrane module is made of a membrane made of polyamide polymer.
(6) The seawater desalination facility according to any one of (1) to (5), further comprising means for adding alkali to the supply water of the second-stage reverse osmosis membrane module.
(7) A seawater desalination method using the seawater desalination facility according to any one of (1) to (6), wherein the concentration of the removal target in the concentrated water flowing into the adsorption resin tower is 5 mg / L or more. A seawater desalination method characterized in that:
(8) The seawater desalination method according to (7), wherein the removal target is boron.
(9) When the space velocity SV is a value obtained by dividing the flow rate of concentrated water in the adsorption resin tower by the adsorption resin volume, SV is 2 to 20H ⁻¹ (7) or (8) The seawater desalination method according to 1.
(10) The seawater desalination method according to any one of (7) to (9), wherein the concentrated water flowing into the adsorption resin tower has a pH of 7 to 10.

  In the two-stage membrane treatment method in which the permeate treated with the reverse osmosis membrane is treated again with the reverse osmosis membrane, the concentrated water of the second-stage reverse osmosis membrane module is treated with the adsorption resin tower, and the reverse of the first stage. By adopting a system that returns to the supply water of the osmosis membrane module, the adsorption resin is highly efficient under the conditions that the concentration of the coexisting ion components that inhibit the adsorption of the adsorption resin is low and the concentration of the object to be removed is high. The processing is possible, and the separation operation with high efficiency becomes possible as a whole. In addition, since the eluate from the adsorbent resin can be removed with a reverse osmosis membrane, application to drinking water or the like that requires safety is also suitable.

  The concentration of seawater in the present invention varies depending on the region. For example, in the case of standard seawater near Japan, the salt concentration is about 35 g / L, the boron concentration is 4 mg / L to 5 mg / L, and high concentrations such as the Middle East. Concentrated seawater may have a salt concentration of about 50 g / L and a boron concentration of 6 mg / L to 7 mg / L.

  The reverse osmosis membrane in the present invention is a separation membrane in a region having a molecular weight separation characteristic of several tens of daltons, and specifically, 90% or more of salt can be removed at an operating pressure of 0.5 MPa or more. Is. The hollow fiber type reverse osmosis membrane used for seawater desalination has a large operating pressure, and the removal rate of salt is generally 99% or more.

  The two-stage reverse osmosis treatment in the present invention is a treatment method in which the raw water is once subjected to the reverse osmosis treatment and the permeated water is again subjected to the reverse osmosis treatment. This is a treatment method for returning to the supply water of the reverse osmosis membrane module in the stage, and a pressure increasing operation is required between the reverse osmosis membrane module in the first stage and the reverse osmosis membrane module in the second stage.

  In the present invention, the first-stage reverse osmosis membrane module and the second-stage reverse osmosis membrane module may have the same characteristics or different characteristics. The removal rate of the second-stage reverse osmosis membrane module is preferably higher than the removal rate of the first-stage reverse osmosis membrane module. Moreover, in order to improve the removal performance in the second stage, an additive may be injected between the first stage and the second stage into the feed water of the second stage reverse osmosis membrane module. For example, in the case of seawater desalination, the boron removal rate is generally not as high as the salt removal rate in the neutral region. However, when alkali is added and the pH is raised to 8.5 or more, boron in water is dissociated and ionized to significantly increase the boron removal rate, so that alkali may be added. In addition, when the first-stage reverse osmosis membrane module has chlorine resistance and residual chlorine exists in the supply water and permeate, a reducing agent may be injected. Examples of the alkali include sodium hydroxide and calcium hydroxide, and sodium hydroxide is most preferable. Examples of the reducing agent include sodium bisulfite and sodium thiosulfate, and sodium bisulfite is most preferable.

  In the present invention, the adsorption resin is an ion exchange resin that adsorbs and removes ions in an aqueous solution by an ion exchange function, a metal ion such as a transition metal or alkaline earth metal in an aqueous solution, or a certain anion. It is a chelate resin that can selectively adsorb and collect specific ionic species by utilizing the action of forming a complex by causing an interaction with a (ligand) and a coordinate bond. Since these functional groups and the material of the base resin are different depending on the target ions, they are not particularly limited. For example, when boron is to be removed, an ion exchange resin having an N-methylglucamine group as a functional group that is a boron adsorbing resin based on a chelate mechanism and a hydrous cerium oxide that is a boron adsorbing resin based on an ion exchange mechanism are used as a polymer substance. Although there is what was carried, etc., it is not particularly limited. Examples of the material of the base resin include, but are not limited to, ethylene vinyl alcohol copolymer, styrene-divinylbenzene copolymer, polystyrene, polyphenol, and cellulose. Those that are durable to acids and alkalis are preferred because they repeatedly come into contact with alkalis and acids during adsorption and desorption (regeneration). For example, in the case of boron, the amount of adsorption increases under alkaline conditions where the pH is about 7 to 10. More preferably, it is in the range of 7.5 to 9.5. In addition, since many impurities are eluted during the treatment, it becomes a problem when the treated water is used for drinking, and in general, activated carbon or the like is placed downstream of the adsorption resin tower as a safety measure when impurities are generated. In the present invention, the treated water by the adsorption resin is returned to the supply water of the first-stage reverse osmosis membrane module, and impurities can be removed by the reverse osmosis membrane module, so that the activated carbon is not necessary. . In addition, in order to prevent microbial contamination in the adsorption resin tower, it may be periodically sterilized with chlorine, which is an oxidizer, but depending on the material of the adsorption resin, the base material may be deteriorated by the oxidizer and impurities. May leak. For example, when a base material obtained by crosslinking a polystyrene material with divinylbenzene is used, the crosslinking agent divinylbenzene may be oxidatively decomposed and impurities may flow out into the treated water of the adsorption resin. In addition, microorganisms may grow in the adsorption resin tower and the microorganisms may flow out into the treated water. However, in the method of returning the treated water of the adsorption resin to the supply water of the reverse osmosis membrane as in the present invention, since it is processed by the reverse osmosis membrane, such impurities and microorganisms can flow out as production water as they are. It can be prevented.

  The shape of the adsorption resin in the present invention is not particularly limited, although there are granular, fibrous, and other shapes. Further, the size of the resin is not particularly limited as long as the performance of the adsorption resin is efficiently expressed.

  In the present invention, the resin tower is not limited in its size, shape, and quantity as long as it can be efficiently treated with an adsorption resin.

  It is preferable that the adsorption capacity of the adsorption resin in the present invention is high. The amount of adsorption per unit amount of the adsorption resin is, for example, in the case of boron, the higher the boron concentration in the liquid to be treated, the larger the amount of adsorption of boron per unit amount of the adsorption resin. A larger tendency is preferable because the effect of the present invention is increased. Since the concentration of boron in the concentrated water in the second-stage reverse osmosis membrane module is higher than that in the permeated water, the effect is greater than when the permeated water is treated. Also, since the first-stage reverse osmosis membrane module permeated water that has been desalted by 99% or more in the first-stage reverse osmosis membrane module and the salt concentration has decreased is treated in the second stage, the second-stage reverse osmosis membrane module The concentration of concentrated water is not so high. Therefore, there are few substances, such as a fluorine ion, a phosphate ion, and a silica which may become an obstacle when adsorption resin adsorbs boron. Further, when removing boron with the second-stage reverse osmosis membrane module, in order to ionize boron into borate ions, generally, alkali is added to the supply water of the second-stage reverse osmosis membrane module to adjust the pH to 8. However, since the concentrated water of the reverse osmosis membrane module in the second stage has a high pH, it is convenient for treatment with an adsorption resin that is adsorbed on the alkali side.

  In the present invention, the concentration of the object to be adsorbed and removed by the adsorption resin tower is preferably 5 mg / L or more, and more preferably 8 mg / L or more. If the concentration is low, the amount of adsorption per adsorbent resin amount is small, and the adsorbent resin may not be used effectively. An example of an adsorption isotherm of boron at pH 8.5 and a water temperature of 20 ° C. is shown in FIG. The higher the concentration of boron in the water to be treated, the more the amount of boron adsorbed per adsorbed resin tends to increase, and the amount of adsorbed boron can be increased even with the same amount of resin. In particular, when the object to be removed is boron, the tendency is large with a cerium-based adsorption resin, which is a preferable example. However, the concentration dependence of the adsorption amount decreases as the boron concentration increases. The boron concentration in sea water is 10 mg / L at the highest, and when the boron removal rate in the first-stage reverse osmosis membrane is 50%, the boron concentration in the permeated water is 5 mg / L. If the recovery rate is 95% when this is treated with the second-stage reverse osmosis membrane, the concentrated water of the second-stage reverse osmosis membrane is concentrated up to 20 times, and the boron concentration is concentrated to a maximum of 100 mg / L. There is a possibility that. Here, when the recovery rate of the reverse osmosis membrane in the second stage is 95% or more, the flow rate in the membrane module and the membrane surface flow rate become small, which is not practical operation. Therefore, in the present invention, it is appropriate that the concentration of the object to be removed in the adsorption resin tower is 100 mg / L or less.

In the present invention, space velocity (SV) is an important operating condition when a removal target is processed in an adsorption resin tower. This space velocity (SV) is a value obtained by dividing the flow rate (L / H) of the liquid to be treated in the adsorption resin tower by the adsorption resin volume (L) of the adsorption resin tower, and has a unit of H- ¹ . Here, the resin volume is an apparent resin volume. If this value is small, the adsorption efficiency with the adsorption resin is high, but if the flow rate of the non-treatment liquid is small or the flow rate of the liquid to be treated is the same, a large amount of the adsorption resin is required, which is not preferable. On the contrary, if the flow rate is large, the flow rate of the liquid to be treated is large and the amount of treatment is large, but the liquid to be treated that flows between the resins in the adsorption resin tower drifts, and the adsorption efficiency may be lowered. Therefore, although depending on the configuration and specifications of the adsorption resin tower, the space velocity (SV) is preferably 2 to 20, and more preferably 5 to 15.

  Examples of the cellulose acetate polymer in the present invention include cellulose acetate, cellulose triacetate, and a mixture of both. From the viewpoint of performance and stability of performance, cellulose triacetate is preferable. Moreover, since these materials are excellent in chlorine resistance, it is possible to add chlorine as a disinfectant to the supply water. Injecting intermittently is preferable because the amount of disinfection by-products and the amount of chemicals used are reduced.

  Examples of the polyamide polymer in the present invention include a linear polyamide polymer, a crosslinked polyamide polymer, and the like, and any may be used as long as the removal performance is excellent. In addition, when removing boron as a 2nd-stage reverse osmosis membrane module, since pH may be used at 8.5 or more, a thing excellent in alkali resistance is preferable and a thing excellent in the removal performance of boron is preferable.

  A first embodiment of the present invention will be described with reference to FIG. In FIG. 1, the total amount of permeated water from the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module, and the total amount of concentrated water from the second-stage reverse osmosis membrane module is treated with an adsorption resin tower. The case where the separation operation is performed by returning to the feed water of the reverse osmosis membrane module at the stage is shown. The feed water 7 of the first-stage reverse osmosis membrane module obtained by combining the raw water 6 with the treated water 13 of the adsorption resin tower is boosted by the high-pressure pump 4 and supplied to the first-stage reverse osmosis membrane module 1. The concentrated water 9 of the first-stage reverse osmosis membrane module is flow-regulated by a flow-regulating valve 18 and discharged out of the system, and the permeated water 8 is pH-adjusted by injecting alkali from the alkali-injecting device 14 and second-stage. The water 10 is supplied to the reverse osmosis membrane module 2, and is pressurized by the low-pressure pump 5 and supplied to the second-stage reverse osmosis membrane module 2. The permeated water 11 is taken out as production water, the concentrated water 12 whose flow rate is adjusted by the flow rate adjusting valve 20 is supplied to the adsorption resin tower 3, and the treated water 13 is returned to the supply water 7 of the first osmosis membrane module 1. Is done.

  FIG. 2 is similar to FIG. 1, and the permeated water 8 of the first-stage reverse osmosis membrane module 1 is supplied to the second-stage reverse osmosis membrane module 2 by the flow rate adjusting valves 19, 21. It is separated into a part 15 that is not treated by the reverse osmosis membrane module 2 of the eye. Depending on the quality of the permeated water of the first-stage reverse osmosis membrane module 1, if it is not necessary to treat the entire amount with the second-stage reverse osmosis membrane module 2, the flow rate adjustment valve 19 is throttled and the flow rate adjustment valve 20 is opened. Thus, it is possible to adjust the amount of water to be treated by the second-stage reverse osmosis membrane module 2, and it is possible to reduce the quantity of the second-stage reverse osmosis membrane module 2.

  FIG. 3 is similar to FIG. 1, and the concentrated water 12 of the second-stage reverse osmosis membrane module 1 is not treated with the feed water 17 of the adsorption resin tower 3 and the adsorption resin by the flow rate adjusting valves 20, 22, 23. Separated into concentrated water 16. By adjusting the flow rate adjusting valves 22 and 23 and discharging the concentrated water of the high-concentration second-stage reverse osmosis membrane module 2, the concentration and the adsorption of the supply water 7 of the first-stage reverse osmosis membrane module 1 are reduced. The amount of resin can be reduced.

  FIG. 4 is similar to FIGS. 2 and 3, and the concentrated water 12 of the reverse osmosis membrane module 2 in the second stage is supplied with the supply water 17 of the adsorption resin tower 3 and the adsorption resin by the flow rate adjusting valves 20, 22 and 23. It is separated into concentrated water 16 which is not treated by the above. As in the case of FIG. 2, depending on the quality of the permeated water of the first-stage reverse osmosis membrane module 1, when it is not necessary to treat the entire amount with the second-stage reverse osmosis membrane module 2, the flow rate adjustment valve 19 is throttled, By opening the flow rate adjusting valve 20, the amount of water to be treated by the second-stage reverse osmosis membrane module 2 can be adjusted, and the number of second-stage reverse osmosis membrane modules 2 can be reduced. Similarly to the case of FIG. 3, by adjusting the flow rate adjusting valves 22, 23 to discharge the concentrated water of the high-concentration second-stage reverse osmosis membrane module 2, the first-stage reverse osmosis membrane module 1 The concentration of the feed water 7 can be reduced and the amount of adsorbed resin can be reduced.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. In addition, an Example shows the case of the reverse osmosis membrane for seawater desalination.

Example 1
In the two-stage reverse osmosis membrane system as shown in FIG. 1, a hollow fiber in which two high-pressure hollow fiber type reverse osmosis membrane elements made of cellulose triacetate are mounted in a pressure vessel as a first-stage reverse osmosis membrane module. Type reverse osmosis membrane module, one HB10255FI manufactured by Toyobo Co., Ltd. As a second-stage reverse osmosis membrane module, an aromatic polyamide spiral reverse osmosis membrane element having an outer diameter of 8 inches is used as a pressure vessel. Using one installed spiral-type reverse osmosis membrane module, the adsorption resin of the adsorption resin tower has boron adsorption performance in the range of boron concentration of 50 to 300 mg / L, that is, boron adsorption per adsorption resin volume. 42 L of an adsorption resin mainly composed of hydrous cerium oxide having an adsorption capacity of 9 g / L (wet resin) was used. Here, the spiral reverse osmosis membrane element has an operating pressure of 0.7 MPa, a temperature of 25 ° C., a salt concentration of 500 mg / L, a recovery rate of 15%, a salt removal rate of 99.7%, and a permeate flow rate of 30 m ³ / day. It is what has. The pretreated seawater from which the seawater has been turbidized by the ultrafiltration membrane module is adjusted to pH 6.5 by sulfuric acid injection, then supplied to the first-stage reverse osmosis membrane module, and NaOH is added to the permeated water. Then, the pH was set to 9 and supplied to the second-stage reverse osmosis membrane module for processing. The pH was measured by the glass electrode method. The concentrated water of the second-stage reverse osmosis membrane module was treated in the adsorption resin tower, and then returned to the supply water of the first-stage reverse osmosis membrane module. Adsorption in the adsorption resin tower had a pH of 9 and a space velocity SV of 14H- ¹ , and two adsorption resin towers divided into three towers were subjected to adsorption treatment and one tower was regenerated with acid. However, the operating conditions in this case were as follows. Raw water seawater temperature 25 ° C., total dissolved substance concentration, TDS concentration 34500 mg / L, boron concentration 4.7 mg / L, first stage operating pressure 7.5 MPa, second stage operating pressure 1.5 MPa, first stage The recovery rate of the reverse osmosis membrane module of the eye is 61.5%, and the recovery rate of the reverse osmosis membrane module of the second stage is 85%. The quality of the produced water obtained as the two-stage treatment, that is, the permeated water of the reverse osmosis membrane module of the second stage is TDS 4 mg / L, boron 0.8 mg / L, which sufficiently satisfies the standard of tap water quality of boron of 1 mg / L or less. It was something to do. The adsorption capacity of boron per adsorption resin volume was 3 g / LR (wet resin). As a result of analyzing the produced water, cerium that was likely to be eluted from the adsorption resin was not detected, and the number of general bacteria was 100 or less. The water quality in the first and second stages is shown in Table 1. Here, the TDS concentration of seawater is a converted value of salinity from electrical conductivity. (Ocean Observation Guidelines (Part 1) Japan Meteorological Agency, 1999, Item 38) The TDS concentration of the permeated water was determined as a soluble evaporation residue according to the weight method (official water method). The boron concentration was measured by an absorptiometric method (water supply official method). The recovery rate indicates the ratio of the permeate flow rate to the feed water flow rate of the reverse osmosis membrane module. Further, the amount of boron adsorbed per adsorbed resin amount was calculated from the resin amount of the adsorbing resin tower, the difference between the boron concentration in the treated water and the boron concentration in the treated water, and the flow rate. Further, cerium was quantified by inductively coupled plasma optical emission spectrometry (ICP method), and when it was 0.02% or less, it was determined as not detected. The number of general bacteria was measured using a standard agar medium method, that is, a method of measuring the number of colonies of bacteria that formed colonies in the medium when cultured at 36 ± 1 ° C. for 24 ± 2 hours.

(Example 2)
Seawater was treated in the same manner as in Example 1 except that the reverse osmosis membrane module was placed in FIG. However, 20% of the concentrated water to the second-stage reverse osmosis membrane module was discharged out of the system without being treated in the adsorption resin tower. The amount of resin was set to 80% so that the amount of treated water per adsorbed resin volume was the same as in Example 1. The quality of the produced water as the two-stage treatment obtained, that is, the water quality of the permeated water 11 of the second-stage reverse osmosis membrane module is TDS 4 mg / L, boron 0.8 mg / L, and the tap water quality standard of boron is 1 mg / L or less Was sufficiently satisfied. The adsorption capacity of boron per adsorption resin volume was 3 g / LR (wet resin). As for the quality of the produced water, cerium was not detected, and the number of general bacteria was 100 / mL or less. In addition, the water quality of the first and second stages are shown in Table 1.

(Example 3)
Implemented except that N-methylglucamine group introduced into porous cross-linked polystyrene substrate, and chelating resin for boron adsorption with a total exchange capacity of 0.6 meq / mL-R (wet resin) or more was used as the adsorption resin Seawater was treated as in Example 1. However, 44 L of adsorbed resin was used. The quality of the produced water as the two-stage treatment obtained, that is, the water quality of the permeated water 11 of the second-stage reverse osmosis membrane module is TDS 4 mg / L, boron 0.8 mg / L, and the tap water quality standard of boron is 1 mg / L or less Was sufficiently satisfied. The adsorption capacity of boron per adsorption resin volume was 2.9 g / LR (wet resin). As a result of analyzing the produced water, no styrene, which is likely to be eluted from the adsorption resin, was detected, and the number of general bacteria was 100 / mL or less. In addition, the water quality of the first and second stages are shown in Table 1. Here, styrene was quantified by the headspace GC-MS method, and was not detected if it was 0.002 mg / L or less.

Example 4
Except for using an MR type styrene-based anion exchange resin having an N-methylglucamine group for adsorption of boron with a total exchange capacity per volume of 0.6 meq / mL-R (wet resin) or more as the adsorption resin. Seawater was treated in the same manner as in Example 1. However, 44 L of adsorbed resin was used. The quality of the produced water as the two-stage treatment obtained, that is, the water quality of the permeated water 11 of the second-stage reverse osmosis membrane module is TDS 4 mg / L, boron 0.8 mg / L, and the tap water quality standard of boron is 1 mg / L or less Was sufficiently satisfied. The adsorption capacity of boron per adsorption resin volume was 2.9 g / LR (wet resin). As a result of analyzing the produced water, no styrene, which is likely to be eluted from the adsorption resin, was detected, and the number of general bacteria was 100 / mL or less. In addition, the water quality of the first and second stages are shown in Table 1.

(Example 5)
Seawater was treated in the same manner as in Example 1 except that a chelating resin having an N-methylglucamine group as a base was used as the adsorption resin. However, since the bulk density was small, SV was carried out at 6H- ¹ . Further, the adsorption capacity of boron per 1 g of dry weight at pH 8 of this chelating agent was 0.73 mmol / g-dry fiber, and the amount of adsorbed resin was 44 kg. The quality of the produced water as the two-stage treatment obtained, that is, the water quality of the permeated water 11 of the second-stage reverse osmosis membrane module is TDS 4 mg / L, boron 0.8 mg / L, and the tap water quality standard of boron is 1 mg / L or less Was sufficiently satisfied. The adsorption capacity of boron per adsorption resin weight was 2.9 g / kg-R (wet resin). Analysis of the produced water revealed no organic matter that could be eluted from the adsorption resin. In addition, the water quality of the first and second stages are shown in Table 1. Here, the organic substance was measured with a TOC meter (automatic measurement: wet oxidation method), and was not detected if it was 5 mg / L or less.

(Example 6)
In the module arrangement of FIG. 1, the two-stage reverse osmosis membrane treatment was performed in the same manner as in Example 1 except that raw water was treated with another adsorption resin and only the boron concentration was reduced to 3.7 mg / L in advance. The quality of the produced water as the two-stage treatment obtained was TDS 4 mg / L, boron 0.6 mg / L, and sufficiently satisfied the standard of tap water quality of boron of 1 mg / L or less. The boron adsorption capacity was 2.8 g / LR (wet resin), and the adsorption efficiency was slightly lower than those of Examples 1 and 2. As for the quality of the produced water, cerium was not detected, and the number of general bacteria was 100 / mL or less. The water quality in the first and second stages is shown in Table 1.

(Comparative Example 1)
5 except that the concentrated water of the second-stage reverse osmosis membrane module was returned to the feed water of the first-stage reverse osmosis membrane module without being treated in the adsorption resin tower. A two-stage reverse osmosis membrane treatment was performed. The quality of the produced water as the obtained two-stage treatment was TDS 4 mg / L and boron 1 mg / L, which satisfied boron tap water quality standards of 1 mg / L or less, but had no margin. As for the quality of the produced water, cerium was not detected, and the number of general bacteria was 100 / mL or less. The water quality in the first and second stages is shown in Table 1.

(Comparative Example 2)
In the module arrangement of FIG. 6, the concentrated water of the second-stage reverse osmosis membrane module is returned to the supply water of the first-stage reverse osmosis membrane module without being treated in the adsorption resin tower, and the second-stage reverse osmosis membrane is A two-stage reverse osmosis membrane treatment was performed in the same manner as in Example 1 except that the permeated water of the module was treated in the adsorption resin tower. The quality of the produced water as the obtained two-stage treatment was TDS 4 mg / L and boron 0.5 mg / L. However, the adsorption capacity of boron per adsorbent resin volume was 2 g / L, and the efficiency of adsorption was significantly lower than in Examples 1 and 2. About 0.03% of cerium, which is considered to be caused by elution from the adsorption resin, was detected in the produced water quality, and the number of general bacteria was 100 / mL or more. For direct use in drinking water, additional treatment such as activated carbon treatment was required. The water quality in the first and second stages is shown in Table 1.

(Comparative Example 3)
In the module arrangement of FIG. 1, the two-stage reverse osmosis membrane treatment was performed in the same manner as in Example 1 except that the raw water was treated with another adsorption resin and only the boron concentration was reduced to 1.6 mg / L in advance. The quality of the produced water as the two-stage treatment thus obtained was TDS 4 mg / L, boron 0.5 mg / L, which sufficiently satisfied the tap water quality standard of 1 mg / L or less of boron. The boron adsorption capacity was 2.2 g / LR (wet resin), and the efficiency of adsorption was significantly lower than in Examples 1 and 2. As for the quality of the produced water, cerium was not detected, and the number of general bacteria was 100 / mL or less. The water quality in the first and second stages is shown in Table 1.

(Comparative Example 4)
A two-stage reverse osmosis membrane treatment was carried out in the same manner as in Comparative Example 2 except that a fiber-like chelate resin based on cellulose similar to that used in Example 5 was used as the adsorbent resin, and the amount of resin was 44 kg. However, SV was carried out at 6H- ¹ . The quality of the produced water as the obtained two-stage treatment was TDS 4 mg / L and boron 0.5 mg / L. However, the adsorption capacity of boron per adsorbent resin weight was 2 g / kg-R (wet resin), which was smaller than that in Example 5, and the efficiency of adsorption was low. In addition, the production water quality was detected at 6 mg / L of organic matter that is considered to be due to elution from the adsorbent resin, and additional treatment such as activated carbon treatment was required for direct use in drinking water and the like. The water quality in the first and second stages is shown in Table 1.

In the seawater desalination method of the present invention, safe and efficient production water with few impurities can be obtained, so that it can be used for drinking water as well as industrial water.

In one example of the treatment method of the present invention, the total amount of permeated water of the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module, and the total amount of concentrated water of the second-stage reverse osmosis membrane module is adsorbed. The simple block diagram in the case of processing in the resin tower and returning to the feed water of the first-stage reverse osmosis membrane module is shown. In an example of the treatment method of the present invention, a part of the permeated water of the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module, and the total amount of concentrated water of the second-stage reverse osmosis membrane module is The simple block diagram in the case of processing in the adsorption resin tower and returning to the feed water of the first-stage reverse osmosis membrane module is shown. In an example of the treatment method of the present invention, the entire amount of permeated water of the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module, and a part of the concentrated water of the second-stage reverse osmosis membrane module is The simple block diagram in the case of processing in the adsorption resin tower and returning to the feed water of the first-stage reverse osmosis membrane module is shown. In one example of the treatment method of the present invention, a part of the permeated water of the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module, and a part of the concentrated water of the second-stage reverse osmosis membrane module. Is a simple configuration diagram in the case where is treated in the adsorption resin tower and returned to the feed water of the first-stage reverse osmosis membrane module. In an example of a conventional treatment method, the total amount of permeated water of the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module, and the total amount of concentrated water of the second-stage reverse osmosis membrane module is one-stage. The simple block diagram in the case of returning to the supply water of the reverse osmosis membrane module of eyes is shown. In an example of a conventional treatment method, the total amount of permeated water in the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module, and the total amount of permeated water in the second-stage reverse osmosis membrane module is adsorbed resin. A simple configuration diagram in the case where the entire amount of concentrated water of the second-stage reverse osmosis membrane module is returned to the supply water of the first-stage reverse osmosis membrane module after being processed in the tower is shown. The figure showing an example of the concentration dependence of the boron adsorption amount of adsorption resin is shown.

Explanation of symbols

1: 1st stage reverse osmosis membrane module 2: 2nd stage reverse osmosis membrane module 3: Adsorption resin tower 4: High pressure pump 5: Low pressure pump 6: Raw water 7: Feed water of 1st stage reverse osmosis membrane module 8 1st stage reverse osmosis membrane module permeated water 9: 1st stage reverse osmosis membrane module concentrated water 10: 2nd stage reverse osmosis membrane module feed water 11: 2nd stage reverse osmosis membrane module permeate Water 12: Concentrated water of the reverse osmosis membrane module of the second stage 13: Treated water of the adsorption resin tower 14: Alkaline injection device 15: Part of the permeated water of the reverse osmosis membrane module of the first stage 16: Reverse of the second stage Part of concentrated water of osmosis membrane module 17: Supply water of adsorption resin tower 18, 19, 20, 21, 22, 23: Flow control valve

Claims (3)

Seawater desalination method in which seawater having a boron concentration of 3.7 to 7 mg / L is treated with a first-stage reverse osmosis membrane module, and at least a part of the permeate obtained is treated with a second-stage reverse osmosis membrane module. The hydrated cerium-containing adsorbent resin tower provided in the path for returning at least a portion of the concentrated water obtained from the second-stage reverse osmosis membrane module to the first-stage reverse osmosis membrane module. PH of 7-10, boron concentration 5-100 mg / L, and the space velocity SV, which is a value obtained by dividing the flow rate of concentrated water in the hydrated cerium hydroxide-containing adsorption resin tower by the adsorption resin volume, is 2-20H- ¹ . A seawater desalination method characterized in that, by treating under conditions, product water having a boron concentration of 1 mg / L or less is obtained . The seawater desalination method according to claim 1 , wherein the first-stage reverse osmosis membrane module comprises a hollow fiber membrane made of a cellulose acetate polymer. The seawater desalination method according to claim 1 or 2, wherein the second-stage reverse osmosis membrane module comprises a membrane made of a polyamide polymer.

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