JP2008161797A - Operation method of freshwater production apparatus, and freshwater production apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical freshwater production method and apparatus which can efficiently remove boron using a semipermeable membrane to obtain freshwater of high water quality. <P>SOLUTION: In the freshwater production method, raw water or pretreated water obtained by pretreating the raw water is treated with a first semipermeable membrane unit (A) to obtain a plurality of streams of permeating water different in water quality a part (a1) of the plurality of the streams of permeating water is treated with a second semipermeable membrane unit (B1), and another stream of permeating water (a2) with water quality different from that of the part (a1) of the streams of permeating water is treated with a third semipermeable membrane unit (B2) with removal performance different from that of the second semipermeable membrane unit (B1). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fresh water production method and a fresh water production apparatus capable of obtaining fresh water from raw water at low cost using a semipermeable membrane such as a reverse osmosis membrane or a nanofiltration membrane, and more specifically, salt content and boron contained in the raw water The present invention relates to a fresh water production method and a fresh water production apparatus capable of efficiently removing desired components.

With the deterioration of the water environment that has become serious in recent years, water treatment technology has become more important than ever, and separation membrane utilization technology has been applied very widely. Seawater desalination has also been put to practical use mainly in the Middle East region, where water resources are extremely small and oil heat resources are extremely abundant. In the region, a desalination process using an energy efficient reverse osmosis membrane is adopted, and many plants have been built and put into practical use in the Caribbean and Mediterranean areas. Furthermore, recently, improvement in reliability and cost reduction have progressed due to technological advances in reverse osmosis, and many reverse osmosis seawater desalination plants have been constructed in the Middle East.
Recently, however, research on the effects of harmful substances on humans has progressed, and the inclusion of trace elements that have been overlooked so far in drinking water has been regulated, and even in seawater desalination, higher water quality is required. It is becoming like that. In particular, boron removal has been highlighted in recent years. Boron is generally contained in seawater in an amount of about 4.5 mg, and problems such as adverse effects on plant growth and infertility have been pointed out, and drinking water guidelines with a WHO of 0.5 mg / l or less are provided. In the Middle Eastern seawater with a high salinity concentration, the boron concentration is also high and becomes a concentration of 5 to 6%. Therefore, removal at a higher rate is required.

However, in the current seawater desalination reverse osmosis membrane, the boron removal rate is at most about 90%, and it cannot be said that it has sufficient boron removal performance. Currently, boron removal in a process using a reverse osmosis membrane is not possible. As a method, once the water that has permeated through the reverse osmosis membrane is treated again with the low pressure reverse osmosis membrane, the permeated water two-stage method (Patent Document 1) and the post-treatment of allowing the boron adsorbent to pass through are combined into a multistage process (Non-Patent Document 1) is adopted. Moreover, as a method for further reducing the boron concentration with a reverse osmosis membrane, an alkali addition method is proposed in which the raw water in the second stage is raised to pH 9.5 or higher to dissociate boron into borate ions and increase the removal rate ( Patent Document 2) has been put into practical use. Furthermore, in the seawater desalination process using reverse osmosis membranes, seawater is concentrated while 5 to 8 reverse osmosis membrane elements are arranged in series to obtain permeate from each element. The permeated water obtained has better water quality than the permeated water obtained by treating concentrated water, that is, the permeated water obtained from the rear. Therefore, a method has been proposed in which the first permeate having relatively good water quality is taken out separately and only the remaining permeate having relatively poor water quality is sent to the second-stage reverse osmosis membrane (Patent Document 3). ). However, if the raw water quality is poor, the reverse osmosis membrane is degraded, or the water quality is likely to deteriorate, the permeated water in the first stage can be maintained sufficiently below the standard even if it is the first one. However, in such a case, everything must be processed in the second stage, so after all, it is equipped with a second stage unit that can handle all the first stage permeate, and usually everything is handled. There is a problem that the equipment becomes expensive because it is not used (that is, useless equipment increases) or the first stage needs to be designed with safety in mind.
JP 2001-269543 A (paragraphs [0038] to [0039]) Japanese Patent No. 3319321 (paragraphs [0006] to [0013]) JP 11-10146 A (Claim 1) J. et al. J. Redondo et al., Desalination, 156, 2003, p229-238.

  The object of the present invention is to solve the above-mentioned problems and to effectively remove TDS and boron by a two-stage treatment using a semipermeable membrane, and to obtain high-quality fresh water at low cost. And providing a fresh water production method and a fresh water production apparatus.

This invention for solving the said subject is characterized by either of following (1)-(9).
(1) Raw water or pretreated water obtained by pretreating raw water is treated with the first semipermeable membrane unit (A) to obtain a plurality of permeated waters having different water qualities, and a part of the plurality of permeated waters While treating (a1) with the second semipermeable membrane unit (B1), another permeated water (a2) having a water quality different from that of part of the permeated water (a1) is supplied to the second semipermeable membrane unit ( The fresh water manufacturing method characterized by processing by the 3rd semipermeable membrane unit (B2) from which removal performance differs from B1).
(2) The fresh water production method according to (1) above, wherein the concentrated water of the second semipermeable membrane unit (B1) is mixed with the supply water of the third semipermeable membrane unit (B2).
(3) The osmotic pressure of the concentrated water of the second semipermeable membrane unit (B1) is 90% to 110% of the osmotic pressure of the permeated water (a2). Fresh water production method.
(4) The first semipermeable membrane unit (A) is composed of at least two subunits (A1) and (A2) having different removal performances, and the permeated water (a1) is obtained from the subunit (A1). The fresh water production method according to any one of (1) to (3), wherein the permeated water (a2) is obtained from the subunit (A2).
(5) The fresh water production method according to (4), wherein the raw water is seawater and the pressure applied to the subunit (A2) is larger than the pressure applied to the subunit (A1).
(6) The fresh water production method according to any one of (1) to (5), wherein the specific component concentration of the permeated water (a1) is lower than the specific component concentration of the permeated water (a2). .
(7) The specific component concentration of the permeated water of the second semipermeable membrane unit (B1) is 90% to 110% of the specific component concentration of the permeated water of the third semipermeable membrane unit (B2). The method for producing fresh water according to any one of (1) to (6).
(8) A first semipermeable membrane unit (A) for treating raw water or pretreated water obtained by pretreating raw water to obtain a plurality of permeated waters having different water qualities, and a part of the plurality of permeated waters A second semipermeable membrane unit (B1) for treating (a1) and a third semipermeable membrane (a2) for treating another permeated water (a2) having a different water quality from part of the permeated water (a1). A fresh water producing apparatus having a permeable membrane unit (B2), wherein the second semipermeable membrane unit (B1) and the third semipermeable membrane unit (B2) have different removal performances.

  According to the present invention, high quality permeated water can be efficiently obtained from raw water. Therefore, for example, fresh water suitable for drinking with reduced boron concentration from seawater can be efficiently obtained at low cost.

  An example of the fresh water producing apparatus of the present invention is shown in FIG. A fresh water producing apparatus shown in FIG. 1 includes a pretreatment means 2 such as a filter for pretreating raw water 1 and a first semipermeable membrane unit 6 (first semipermeable membrane unit (A)) for treating pretreated water. ), A second semipermeable membrane unit 14 (second semipermeable membrane unit (B1)) for treating a part of the permeated water obtained from the first semipermeable membrane unit 6, and the first A third semipermeable membrane unit 21 (third semipermeable membrane unit (B2)) for treating the remaining permeated water obtained from the semipermeable membrane unit 6 is configured as a main device.

  Each semipermeable membrane unit is not particularly limited, but in order to facilitate handling, a hollow fiber membrane-like or flat membrane-like semipermeable membrane is housed in a housing to form a fluid separation element (element). It is preferable to use the one loaded in. When the fluid separation element is formed of a flat membrane, for example, as shown in FIG. 5, a semipermeable membrane 43 and a permeate flow passage material such as a tricot around a cylindrical central pipe 42 having a large number of holes. It is preferable to wind a membrane unit including 45 and a supply water flow path member 44 such as a plastic net, and to store these in a cylindrical casing. In the fluid separation element, the supply water 38 is supplied into the unit from one end, and passes through the semipermeable membrane 43 until reaching the other end, and the permeated water 40 that has permeated passes through the central pipe 42. To the center pipe 42 at the other end. On the other hand, the supply water 38 that has not permeated the semipermeable membrane 43 is taken out as concentrated water 39 at the other end. In addition, it is also preferable to configure a semipermeable membrane unit by connecting a plurality of fluid separation elements in series or in parallel. FIG. 6 illustrates a cross-sectional view of a semipermeable membrane unit in which a plurality of fluid separation elements shown in FIG. 5 are connected in series and loaded into a pressure vessel. In this figure, the central pipe 42 of each fluid separation element 46 is connected by a pipe joint 48, and when the supply water 38 sequentially passes through the fluid separation element 46, it passes through the membrane, and the water is collected in the central pipe 42. It is structured to be taken out as permeated water 40.

  As the material of the semipermeable membrane 43, a polymer material such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer, or the like can be used. The membrane structure has a dense layer on at least one side of the membrane, and on the asymmetric membrane having fine pores with gradually increasing pore diameters 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.

  And in FIG. 1, the 1st semipermeable membrane unit 6 is comprised so that the some permeated water from which water quality differs can be obtained. That is, a plug is interposed between the central pipes of a plurality of fluid separation elements constituting the first semipermeable membrane unit 6, and the permeated water with good water quality obtained from the upstream fluid separation element is discharged from the upstream end of the unit. The permeated water with poor water quality obtained from the downstream fluid separation element (permeated water obtained by treating the concentrated water while passing through the upstream fluid separation element) is removed from the downstream end of the unit. It is configured as follows. Specifically, as shown in FIG. 8, the permeated water outlet 50 is provided at both ends of the pressure vessel, the permeated water of the upstream fluid separation element with good water quality is taken out from the upstream outlet 50, and the rest is removed. It is configured to take out from the takeout port 50 on the downstream side. In this way, the permeated water of the first semipermeable membrane unit 6 can be divided.

  Moreover, in FIG. 1, the 2nd semipermeable membrane unit 14 and the 3rd semipermeable membrane unit 21 are comprised so that removal performance may mutually differ according to the quality of the water supplied to these units.

Further, in FIG. 1, scale preventing agent adding means 3, 10, 18 and pH adjusting means 4, 12, 19 is provided. The scale inhibitor addition means is preferably arranged upstream of the pH adjustment means. The scale inhibitor adding means and the pH adjusting means are not particularly limited, and a general chemical injection pump can be used. Although not shown, an in-line mixer may be provided immediately after the pH adjusting means, or a sudden pH change in the vicinity of the addition port may be prevented by making the addition port directly contact the flow of the supply water. preferable. The pH adjusting means is not essential in the practice of the present invention. For example, when the purpose is to remove boron, boron is ionized by adding alkali, and the removal rate of the semipermeable membrane is increased. However, since it is particularly easy for scales to precipitate in the alkaline state, it is necessary to consider the combined use of a scale inhibitor as described above.
And although it is not essential in implementation of this invention in FIG. 1, in order to collect | recover the energy which concentrated water holds according to economical efficiency, the concentrated water (primary concentrated water 25) of the 1st semipermeable membrane unit 6 is collected. An energy recovery means on the side is also provided.

  In such a fresh water production apparatus, the raw water 1 is first supplied by the first booster pump 5 after being pretreated by the pretreatment means 2 as it is or according to its turbidity. A plurality of primary permeates 7 and 16 (permeate (a1) and (a2)) having different water qualities are obtained and stored in the intermediate tanks 8 and 17, respectively. The primary permeate 7 (permeate (a1)) stored in the first intermediate tank 8 is sent to the second semipermeable membrane unit 14 by the second booster pump 13, and the first secondary permeate 15 is obtained. Is obtained. On the other hand, the primary permeated water 16 (permeated water (a2)) stored in the second intermediate tank 17 is removed by the third semi-permeable membrane unit 14 from the second semi-permeable membrane unit 14 and the third semi-permeable membrane. The second secondary permeated water 22 is obtained by being sent to the membrane unit 21. As described above, in the present invention, even in the permeated water obtained by the first semipermeable membrane unit 6, there is a difference in water quality between the permeated water obtained from the upstream fluid separation element and the permeated water obtained from the downstream fluid separation element. Paying attention to certain things, they are taken out separately and further processed separately by the second semipermeable membrane unit 14 and the third semipermeable membrane unit 21 having removal performance suitable for each water quality. This makes it possible to achieve a highly required water quality economically.

  In addition, although the handling of the concentrated water 32 of the second semipermeable membrane unit and the concentrated water 23 of the third semipermeable membrane unit is not particularly limited, in FIG. 1, the drain valves 33 and 34 are opened. Can be discharged out of the system, and since it is originally concentrated water of the first semipermeable membrane unit, if there is no problem with water quality, the reflux valve 30 or 31 is opened and returned to the raw water line. It is also possible to send it to the first semipermeable membrane unit. Of course, there is no problem whether only one of them is refluxed or both are refluxed according to the water quality and necessity. Further, the amount and ratio of the treatment performed by the second semipermeable membrane unit 14 and the third semipermeable membrane unit 21 are not particularly limited, but the water quality in the final permeated water tank 24 should be satisfied. It is necessary. If the permeated water quality of the first semipermeable membrane unit 6 is sufficiently good, a part of the primary permeated water can be sent to the final product water tank 24 as it is by opening the bypass valve 28.

  Moreover, it is also preferable to add the scale inhibitor for preventing the scale precipitation by concentration, the acid for adjusting pH, and the alkali to the supply water of each semipermeable membrane unit as needed.

  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.

  On the other hand, sulfuric acid, sodium hydroxide, and calcium hydroxide are generally used as the acid and alkali, but hydrochloric acid, oxalic acid, potassium hydroxide, sodium bicarbonate, ammonium hydroxide, and the like can also be used. However, it is better not to use calcium or magnesium in order to prevent an increase in scale components in seawater.

  Alkaline is effective when added to the water supply of any semipermeable membrane unit, but from the viewpoint of operating costs, the first semipermeable membrane unit has a higher raw water flow rate, so the alkali is added. In addition, when the recovery rate is generally lower than the recovery rate of the second semipermeable membrane unit 14, the flow rate of concentrated water that becomes drainage increases and the wastewater treatment cost also increases. Alternatively, it is preferable to add alkali preferentially to the water supplied to the third semipermeable membrane unit. The allowable range of alkali addition here is appropriately set according to the alkali resistance of the semipermeable membrane, the allowable range for the risk of scale generation due to alkali addition, and the cost of addition of alkali and scale inhibitor.

  The present invention as described above can be implemented with the following modifications, for example. That is, the water quality of the permeated water 15 of the second semipermeable membrane unit and the permeated water 22 of the third semipermeable membrane unit is determined by the operating conditions of the first semipermeable membrane unit 6 and the method of dividing the primary permeated water 7 and 16. The second semipermeable membrane unit 14 and the third semipermeable membrane unit 21 can be changed depending on the membrane performance and operating conditions. Therefore, for example, when the permeated water 15 of the second semipermeable membrane unit is used as drinking water and the permeated water 22 of the third semipermeable membrane unit is used as non-potable water, the final product water as shown in FIG. It is also possible to divide the tank into two types. The form shown in FIG. 2 is the same as the form shown in FIG. 1 except for the points described above, although the explanation is omitted.

  In addition, when the permeated water 15 of the second semipermeable membrane unit and the permeated water 22 of the third semipermeable membrane unit are used for one application, specific components in the permeated water 15 of the second semipermeable membrane unit. When the concentration is 90% or more and 110% or less of the specific component concentration in the permeated water 22 of the third semipermeable membrane unit, energy loss due to mixing can be suppressed, which is economically preferable. The specific component concentration is the concentration of a substance to be removed such as total salinity, boron, bromine, fluorine, ammonia, nitric acid, and silica, although it varies depending on the desired water quality of the production water and the purpose of use.

  Further, when both the concentrated water 32 of the second semipermeable membrane unit and the concentrated water 23 of the third semipermeable membrane unit are refluxed, it is economical to make the osmotic pressures substantially the same. That is, when the osmotic pressure ratio in the primary permeate 7 (a1) and 16 (a2) is a1: a2 = 1: α, the recovery rate R2 of the second semipermeable membrane unit and the recovery of the third semipermeable membrane unit The recovery rate may be set so that the relationship of the rate R3 is R3 = α × R2−α + 1.

  As a method of dividing the primary permeated water 7 and 16, it is preferable to divide the first semipermeable membrane unit at a portion having good water quality and a portion having relatively poor water quality. As a method for realizing this, in addition to the method described above, the first semipermeable membrane unit 6 is divided into a front subunit 36 and a rear subunit 37 as illustrated in FIG. Compared with the previous stage, the permeated water with good water quality obtained from the low feed water (permeated water obtained from the subunit 36 in the previous stage) is sent to the second semipermeable membrane unit 14 and becomes the concentrated water in the former subunit 36. A method of sending permeated water having relatively poor water quality (permeated water obtained from the downstream subunit 37) to the third semipermeable membrane unit 21 may be mentioned. In this case, as shown in FIG. 4, a booster pump 54 can be provided between the subunit 36 and the subunit 37, and it is also preferable to obtain the power of the booster pump from the energy recovery unit 26. 3 and FIG. 4 is the same as the embodiment shown in FIG. 1 except for the points described above, although the explanation is omitted.

  Further, as shown in FIG. 9, in order to control the flow rate of the permeated water taken out from the upstream fluid separation element and the permeated water taken out from the downstream fluid separation element, at least one of the first semipermeable membrane units 6 is taken out. It is also possible to divide the permeated water into two by providing flow control valves 47 and 51 at the port 50 or by shielding one of the pipe joints 48 connecting the fluid separation element with a plug 49 or the like. .

  Further, the removal performance of the third semipermeable membrane unit 21 for processing the permeated water obtained from the downstream fluid separation element having poor water quality is the same as that for treating the permeated water obtained from the preceding fluid separation element having good water quality. A higher performance than the removal performance of the second semipermeable membrane unit 14 is preferable because the water quality of the second semipermeable membrane unit 14 and the third semipermeable membrane unit 21 are close to each other. Specifically, if it is necessary to remove the semi-permeable membrane housed in the second semi-permeable membrane unit 14 to a highly water-permeable type or to remove a substance whose removal rate increases when it is made alkaline such as boron, for example, This can be realized by setting the supply water of the third semipermeable membrane unit 21 to a higher pH than the supply water of the second semipermeable membrane unit 14. Furthermore, it is more preferable that the semipermeable membrane housed in the second semipermeable membrane unit 14 is of a high water permeability type because it can be operated at a low pressure and the power cost can be reduced.

  Depending on the concentration relationship between the supply water and the concentrated water of the second semipermeable membrane unit 14 and the third semipermeable membrane unit 21, each concentrated water can be simply circulated as the supply water of the first semipermeable membrane unit 6. For example, it is also preferable to mix the concentrated water 32 of the second semipermeable membrane unit with the supply water of the third semipermeable membrane unit 21 as illustrated in FIG. In particular, a portion having good water quality is taken out as the primary permeate 7, and the concentration of the concentrated water 32 of the second semipermeable membrane unit is 90% or more and 110% or less of the TDS concentration of the primary permeate 16 having the poor water quality. Thus, it is preferable to set the recovery rate of the second semipermeable membrane unit 14 and to mix the concentrated water 32 of the second semipermeable membrane unit with the supply water of the third semipermeable membrane unit 21. As a result, energy loss due to mixing of water having different concentrations can be reduced.

In the present invention, although not particularly limited, the permeated water quality and the permeated water amount are as high as possible without causing unnecessary damage to the fluid separation element constituted by the semipermeable membrane, the supporting member, the flow path material, and the like. It is preferable to maintain the level. Regarding the permeate quality, generally, the removal performance of the semipermeable membrane decreases as the temperature increases. Generally, in order to improve the permeate quality by changing the operating conditions, the concentration polarization is reduced by lowering the concentration rate of raw water (= reducing the recovery rate), increasing the raw water flow rate, or increasing the permeate flow rate per membrane area. Although the method of reducing can be taken, all have a subject. Lowering the recovery rate decreases the permeate flow rate. Increasing the raw water flow rate increases the pressure loss due to the high flow rate, increases the energy loss, and increases the possibility of damaging the semipermeable membrane element. When the permeate flow rate per membrane area is increased, dirt tends to accumulate on the membrane surface, which tends to adversely affect the lifetime of the membrane. Further, when the permeated water amount is increased, it can be achieved by increasing the raw water flow rate or increasing the recovery rate, but it is necessary to be careful because the possibility of damaging the semipermeable membrane element is increased.
Furthermore, in general, the semipermeable membrane unit is often configured by connecting a large number of fluid separation elements in series, but in this case, there is a difference in permeate flow rate per membrane area in each fluid separation element. The permeate flow rate per membrane area increases as the pressure difference to the semipermeable membrane increases, and increases as the raw water concentration decreases, but in general, the permeate flow rate is the highest in the leading fluid separation element. Become. Therefore, in general, care must be taken not to exceed the maximum amount of water produced per fluid separation element recommended by the semipermeable membrane manufacturer. As for the method that does not increase the permeation flux, it can be solved by increasing the area of the semipermeable membrane, that is, increasing the number of fluid separation elements. is required.

  In the configuration in which a plurality of fluid separation elements are connected in series, it is not easy to measure the leading permeate flow rate. Ideally, the permeate flow rate of the leading fluid separation element is most directly and preferably measured with the same raw water and the same operating conditions, with the number of fluid separation elements being one, but Reference 1 It is also a more preferable method in designing to estimate by simulation by the method shown in (M. Taniguchi et al., Journal of Membrane Science, Vol. 183, 2000, p249-258).

  By the way, the raw water suitable for the present invention is not particularly limited to seawater, brine, river water, ground water, drainage and treated water, and can be applied to various raw waters.

  In the case of raw water containing a high concentration of solute such as seawater, it is necessary to use a high-pressure pump to raise the supply water to the first semipermeable membrane unit 6 in consideration of the osmotic pressure. Since the osmotic pressure of the supplied water becomes very high as it is processed by the permeable membrane unit 6, it is necessary to increase the pressure resistance of the first semipermeable membrane unit 6. Therefore, as a fluid separation element used for the first semipermeable membrane unit 6, for example, TM800 series manufactured by Toray Industries, Inc. is suitable. In this case, since the water supplied to the second and third semipermeable membrane units 21 has a low concentration, a low pressure specification semipermeable membrane unit, for example, TM700 series manufactured by Toray Industries, Inc. is suitable.

  On the other hand, when a semipermeable membrane having a relatively low blocking performance called a so-called nanofiltration membrane is used as the first semipermeable membrane unit 6, the molecule or membrane having a relatively large molecular weight is charged while reducing the influence of osmotic pressure. Multivalent ions with high repulsion can be efficiently removed. In particular, multiply-charged ions often cause scale generation, and if scale components are removed by the first semipermeable membrane unit, scale generation in the second and third semipermeable membrane units can be suppressed, and high Recovery can be achieved.

  In the present invention, the supply water supplied to the first semipermeable membrane unit 6 is preferably clear so that the accumulation of dirt on the semipermeable membrane surface is reduced. For this purpose, first, it is preferable that the quality of the intake water itself is good, but when surface water is contaminated, it is also preferable to obtain permeated water such as groundwater. Moreover, in this invention, it is preferable to give pretreatments, such as removal of a turbid component, and disinfection, as needed for the supply water supplied to the 1st semipermeable membrane unit 6. By these treatments, it is possible to prevent the performance degradation of the semipermeable membrane units 6, 14, 21 and the subsequent process, and the treatment 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 supply water.

  When it is necessary to remove the turbidity of the feed water, it is effective to apply sand filtration, microfiltration membrane, or ultrafiltration membrane. At this time, when there are many microorganisms such as bacteria and algae, it is also preferable to add a bactericidal agent. Chlorine is preferably used as the disinfectant, and for example, chlorine gas or sodium hypochlorite may be added to the feed water so as to be in the range of 1 to 5 mg / l as free chlorine. In addition, depending on the semipermeable membrane, the specific bactericidal agent may not have chemical durability, so in that case, it is added on the upstream side with respect to the flowing direction of the feed water as much as possible, and further, the first semipermeable membrane unit It is preferable to invalidate the disinfectant in the vicinity of the feed water inlet side of 6. For example, in the case of free chlorine, its concentration is measured, and the addition amount of chlorine gas and sodium hypochlorite is controlled based on this measured value, or a reducing agent such as sodium bisulfite is added. 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 the semipermeable membrane unit can be obtained. In particular, when adding the flocculant, it is preferable to adjust the pH so as to facilitate aggregation.

  On the other hand, if the supply water contains a lot of soluble organic matter, it can be decomposed by adding chlorine gas or sodium hypochlorite, but it can also be done by pressurized flotation or activated carbon filtration. Removal is possible. 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.

  It is also possible to use a nanofiltration membrane or a reverse osmosis membrane for the pretreatment for the purpose of removing specific ions or polymers in advance and operating the fresh water production apparatus of the present invention with high efficiency.

In the implementation, the total salt concentration in the permeated water and the supply water is determined by measuring the electric conductivity of each solution with an electric conductivity meter (SC82 manufactured by Yokogawa Electric) and measuring the simulated sea water concentration and electric conductivity measured in advance with simulated sea water. It was obtained from the relational expression. Simulated seawater here refers to NaCl = 23.926 g / l, Na ₂ SO ₄ = 4.006 g / l, KCl = 0.338 g / l, NaHCO ₃ = 0.196 g / l, MgCl ₂ = 5.072 g / L, CaCl ₂ = 1.147 g / l, H ₃ BO ₃ = 0.0286 g / l. The total salt concentration when adjusted at this concentration is 3.5% by weight.
The boron concentration in the feed water and permeated water was measured with an ICP emission analyzer (P-4010 manufactured by Hitachi, Ltd.), and the pH was measured using a PH82 manufactured by Yokogawa Electric.

<Comparative Example 1>
The flow of the evaluation apparatus used for the comparative example is shown in FIG. The evaluation apparatus includes pretreatment means 2 by coagulating sand filtration, first semipermeable membrane unit supply water tank 53, high pressure pump 5, first semipermeable membrane unit 6, booster pump 13, and second semipermeable membrane unit 14. The third semipermeable membrane unit 21 is used. The flow rate of the high-pressure pump 5 is output controlled by an inverter, and the outputs of the booster pumps 13 and 20 are not adjusted, but are substantially controlled by the flow rate adjusting valves 56 and 57. The flow rate of the primary permeated water 7 of the first semipermeable membrane unit 6 is adjusted by the first semipermeable membrane unit concentrated water flow rate adjusting valve 27, and the second semipermeable membrane unit 14 and the third semipermeable membrane unit 21. The permeated water flow rate was adjusted by circulating water reflux valves 30 and 31, respectively. All the concentrated water of the second semipermeable membrane unit 14 and the third semipermeable membrane unit 21 was returned to the first semipermeable membrane unit supply water tank 53. As the first semipermeable membrane unit 6, six high-pressure reverse osmosis membrane elements TM810 (diameter 10 cm, total length 1 m) manufactured by Toray Industries, Inc. were connected in series as shown in FIG. As the second semi-permeable membrane unit 14, two low-pressure reverse osmosis membrane elements TM710 (diameter 10 cm, total length 1 m) manufactured by Toray Industries, Inc., connected in series and loaded in a pressure vessel, two parallel, As the third semipermeable membrane unit, two TM710s connected in series and loaded in a pressure vessel were made into one row.

Using this equipment, seawater near the Toray Industries Inc. Ehime Plant (salt concentration = 35,600 mg / l, boron concentration 4.7 mg / l, temperature 29 ° C., pH = 7.6 as raw water) The semipermeable membrane unit 6 has a supply water flow rate of 100 m ³ / day, the primary permeate flow rate 40 m ³ / day (recovery rate 40%), and the second semipermeable membrane unit 14 has a supply water flow rate of 26.67 m ³ / day. day, permeate flow rate 22m ³ / day (recovery rate 82.5%), the third semi-permeable membrane unit 21 the supply water flow rate 13.33m ³ / day, permeate flow rate 11m ³ / day (recovery rate 82.5 At this time, since the flow rate of the concentrated water in the second semipermeable membrane unit 14 was 7 m ³ / day, the consumption of seawater was 93 m ³ / day.

As a result of the operation, as a whole device, the seawater intake amount was 93 m ³ / day, the production water amount was 33 m ³ / day, the salt concentration of the production water was 6.2 mg / l, and the boron concentration was 0.54 mg / l. The operating pressure of the first semipermeable membrane unit 6 was 5.5 MPa, and the operating pressure of the second semipermeable membrane unit 14 was 1.02 MPa.

<Example 1>
The evaluation apparatus shown in FIG. 11 was configured. That is, the first semipermeable membrane unit in the evaluation apparatus of FIG. 10 is provided with a permeate outlet 50 and permeate flow rate adjusting valves 47 and 51 on both sides so that the permeate can be divided as shown in FIG. The primary permeate 7 on the upstream side of the first semipermeable membrane unit and the primary permeate 16 on the downstream side can be separately taken out from both ends of the pressure vessel. In addition, an ultra-low pressure reverse osmosis membrane element TMG10 (diameter 10 cm, total length 1 m) manufactured by Toray Industries, Inc. is used as the second semipermeable membrane unit 14 for treating the upstream primary permeate 7. The concentrated water 32 was sent to the third semipermeable membrane unit supply water tank 17, mixed with the primary permeated water 16, and supplied to the third semipermeable membrane unit 21.

Using this apparatus, as in Comparative Example 1, the apparatus was operated such that the production water volume was 33 m ³ / day with respect to the seawater intake volume 93 m ³ / day. Specifically, the flow rate of the supply water of the first semipermeable membrane unit 6 and the sum of the primary permeate water 7 and the primary permeate water 16 are the same as in Comparative Example 1, and the flow rate of the concentrated water 23 is compared. It was set to 7 m ³ / day so as to obtain the same reflux rate as in Example 1. Further, the flow rate of the upstream side of the primary permeate 7 of the first semi-permeable membrane unit, the flow rate on the downstream side of the primary permeate 17 are each 25 m ³ / day by permeated water flow control valve 47, 51, ^{15 m} 3 / The day was adjusted. Subsequently, the supply water flow rate of the second semipermeable membrane unit 14 is 25 m ³ / day, which is the same as the flow rate of the upstream primary permeate 7, and the recovery rate is 50%, that is, the permeate flow rate is 12.5 m ³ / day. Controlled on the day. The flow rate of the supply water of the third semipermeable membrane unit 21 is the sum of the flow rate of 15 m ³ / day of the downstream primary permeate 16 and the flow rate of 12.5 m ³ / day of the concentrated water 32 of the second semipermeable membrane unit. It was made to become. That is, since the concentrated water flow rate of the third semipermeable membrane unit 21 is set to 7 m ³ / day as described above, the flow rate of the permeated water 22 is 20.5 m ³ / day, and the total product water flow rate is The sum of the permeated water 15 of the second semipermeable membrane unit and the permeated water 22 of the third semipermeable membrane unit is 33 m ³ / day, which is the same amount of product water as in Comparative Example 1.
As a result of the operation, the salt concentration of the produced water was 4.2 mg / l (2/3 times that of Comparative Example 1), and the boron concentration was 0.49 mg / l (9/10 times that of Comparative Example 1). Compared to the above, good water quality was obtained. The operating pressure of the first semipermeable membrane unit 6 was 5.6 MPa, which is slightly higher than that of Comparative Example 1, but the operating pressure of the second semipermeable membrane unit 14 was 0.32 MPa and the third semipermeable membrane unit 6 was. The operating pressure of the membrane unit was 0.95 MPa, and both were smaller than the comparative example.

It is a schematic flowchart which shows one embodiment of the fresh water manufacturing apparatus which concerns on this invention. It is a general | schematic flowchart which shows one embodiment of the fresh water manufacturing apparatus which concerns on this invention (The aspect which divided | segmented final permeate water into two types). It is a schematic flowchart which shows one embodiment of the fresh water manufacturing apparatus (a mode in which the first semipermeable membrane unit is divided into two stages) according to the present invention. It is a schematic flowchart which shows one embodiment of the fresh water manufacturing apparatus (mode which pressure | voltage-rises by the 2nd step | paragraph of a 1st semipermeable membrane unit) concerning this invention. It is an example of the fluid separation element which can be used for the fresh water manufacturing apparatus which concerns on this invention. It is an example of the semipermeable membrane unit which can be used for the fresh water manufacturing apparatus which concerns on this invention. It is a schematic flowchart which shows one embodiment of the fresh water manufacturing apparatus which concerns on this invention (The aspect which uses the concentrated water of a 2nd semipermeable membrane unit as the supply water of a 3rd semipermeable membrane unit). It is an example of the 1st semipermeable membrane unit suitable for the fresh water manufacturing apparatus which concerns on this invention. It is another example of the 1st semipermeable membrane unit suitable for the fresh water manufacturing apparatus which concerns on this invention. It is a flowchart of the conventional fresh water manufacturing apparatus applied by the comparative example. It is a flowchart of the fresh water manufacturing apparatus based on this invention applied in the Example.

Explanation of symbols

1: Raw water 2: Pretreatment means 3: First scale inhibitor addition means 4: First alkali addition means (pH adjustment means)
5: First semipermeable membrane unit booster pump 6: First semipermeable membrane unit 7: Primary permeated water (permeated water (a1)) of the first semipermeable membrane unit
8: Second semipermeable membrane unit supply water tank (intermediate tank)
10: Second scale inhibitor addition means 12: Second alkali addition means (pH adjustment means)
13: Second semipermeable membrane unit booster pump 14: Second semipermeable membrane unit 15: Second semipermeable membrane unit permeated water (first secondary permeated water)
16: Primary permeate of the first semipermeable membrane unit (permeate (a2))
17: Third semipermeable membrane unit supply water tank (intermediate tank)
18: Third scale inhibitor addition means 19: Third alkali addition means (pH adjustment means)
20: Third semipermeable membrane unit booster pump 21: Third semipermeable membrane unit 22: Third semipermeable membrane unit permeated water (second secondary permeated water)
23: Third semipermeable membrane unit concentrated water 24: Final permeate tank (product water tank)
25: Concentrated water of the first semipermeable membrane unit (primary concentrated water)
26: Energy recovery unit 27: First semipermeable membrane unit concentrated water flow rate adjustment valve 28: First semipermeable membrane unit permeated water (a1) Bypass valve 29: First semipermeable membrane unit permeated water (a1) flow rate Control valve 30: Second semipermeable membrane unit concentrated water reflux valve 31: Third semipermeable membrane unit concentrated water reflux valve 32: Second semipermeable membrane unit concentrated water 33: Second semipermeable membrane unit concentrated water Drain valve 34: Third semipermeable membrane unit concentrated water drain valve 35: Second final permeate tank (product water tank)
36: Sub-unit front stage (A1) of the front stage
37: Sub-unit rear stage (A2)
38: Supply water 39: Concentrated water 40: Permeated water 41: Sealing material 42: Center pipe 43: Semipermeable membrane 44: Supply water channel material 45: Permeated water channel material 46: Fluid separation element 47: Permeated water flow rate adjustment valve 48 : Pipe joint 49: Plug 50: Permeated water outlet 51: Permeated water flow rate adjustment valve 52: Pressure vessel 53: First semipermeable membrane unit supply water tank 56: Second semipermeable membrane unit supply water flow rate adjustment valve 57: Third semipermeable membrane unit supply water flow rate adjustment valve

  The operation method of the fresh water production apparatus of the present invention efficiently removes TDS and boron by a two-stage treatment using a semipermeable membrane, and enables production of fresh water with high quality at low cost.

Claims (8)

Raw water or pretreated water obtained by pretreatment of raw water is treated with the first semipermeable membrane unit (A) to obtain a plurality of permeated waters having different water qualities, and a part of the permeated waters (a1) Is treated with the second semipermeable membrane unit (B1), and another permeated water (a2) having a water quality different from that of a part (a1) of the permeated water is treated with the second semipermeable membrane unit (B1). Is treated with a third semipermeable membrane unit (B2) having different removal performance. The fresh water production method according to claim 1, wherein the concentrated water of the second semipermeable membrane unit (B1) is mixed with the supply water of the third semipermeable membrane unit (B2). The fresh water production method according to claim 2, wherein the osmotic pressure of the concentrated water of the second semipermeable membrane unit (B1) is 90% or more and 110% or less of the osmotic pressure of the permeated water (a2). The first semipermeable membrane unit (A) is composed of at least two subunits (A1) and (A2) having different removal performances, and the permeated water (a1) is obtained from the subunit (A1). The fresh water production method according to claim 1, wherein the permeated water (a2) is obtained from (A2). The fresh water production method according to claim 4, wherein the raw water is seawater and the pressure applied to the subunit (A2) is larger than the pressure applied to the subunit (A1). The method for producing fresh water according to any one of claims 1 to 5, wherein the specific component concentration of the permeated water (a1) is lower than the specific component concentration of the permeated water (a2). The specific component concentration of the permeated water of the second semipermeable membrane unit (B1) is 90% to 110% of the specific component concentration of the permeated water of the third semipermeable membrane unit (B2). Item 7. The fresh water production method according to any one of Items 1-6. A first semipermeable membrane unit (A) for treating raw water or pretreated water obtained by pretreating raw water to obtain a plurality of permeated waters having different water qualities, and a part (a1) of the plurality of permeated waters A third semipermeable membrane unit (B1) for treating water and a third semipermeable membrane unit for treating another permeated water (a2) having a water quality different from that of part of the permeated water (a1) (B2) and the second semipermeable membrane unit (B1) and the third semipermeable membrane unit (B2) have different removal performance from each other.

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