HK1065994B - Water processing method and apparatus - Google Patents

Description

Water treatment method and water treatment apparatus

Technical Field

The present invention relates to a water treatment apparatus having a reverse osmosis membrane module and a boron removal device, and a water treatment method using the same.

Background

In the production of fresh water from seawater or water, or purified water from river water or lake water, etc., water treatment facilities having a reverse osmosis membrane module are generally used. Basically, as shown in fig. 1, this water treatment facility pressurizes raw water (seawater or the like) subjected to a pretreatment such as sterilization and removal of turbid components to a predetermined pressure (for example, about 6.0 Mpa) by a high-pressure pump 1 to supply the raw water to a reverse osmosis membrane module 2, and separates the raw water into permeate (fresh water) and concentrate by reverse osmosis. The obtained permeated water has a quality that can substantially satisfy the WHO water quality index value, but is not satisfactory in terms of boron.

The boron exists in the seawater in the form of boric acid, and the content of the boron is about 4-5 mg/L. With a currently commercially available reverse osmosis membrane module for sea water desalination, depending on conditions, it may be difficult to keep the boron concentration at or below a provisional value (0.5mg/L) of the boron concentration specified by the WHO water quality index.

Thus, Japanese patent application laid-open No. 9-10766 discloses a water treatment method in which seawater is supplied to a 1 st reverse osmosis membrane module, and the obtained permeate is adjusted to pH5.7 or more and then supplied to a 2 nd reverse osmosis membrane module.

However, in the reverse osmosis membrane method, since only the separated concentrate is discharged, the amount of permeate obtained, that is, the generation efficiency, is limited with respect to the feed water. Therefore, in order to secure the same amount of treated water as that in the case where the 2 nd reverse osmosis membrane module is not provided, that is, the case where boron remaining in the permeated water is not removed, it is necessary to additionally treat about 10% or more of water in the 1 st reverse osmosis membrane module, which results in an increase in equipment expenses and electricity expenses, and thus is uneconomical.

On the other hand, as a method for removing boron, in addition to the reverse osmosis membrane method, a method of adsorption-removal using a strongly basic anion exchange resin or a method of adsorption-removal using a resin produced by binding a styrene-divinylbenzene copolymer to methylglucamine are known. Japanese patent application laid-open No. 10-15356 discloses a water treatment method for removing boron by causing the permeated water of a reverse osmosis membrane module to flow through an ion exchange resin layer by reverse osmosis. In this case, the water treatment efficiency of the ion exchange resin layer can be 96% or more than 96%, which indicates that it is effective. However, since the equipment cost of the adsorption column and the like, the initial investment of the resin, and the regeneration cost of the resin are high, there is a problem in terms of economy.

Disclosure of Invention

It is an object of the present invention to provide an economical water treatment method and water treatment apparatus for removing boron from water containing boron.

The present invention is a water treatment method comprising a step of separating water containing boron with a reverse osmosis membrane module to obtain permeated water and a step of subjecting a part of the obtained permeated water to boron removal with an adsorbent, wherein the water subjected to the boron removal treatment is mixed with water not subjected to the boron removal treatment in the permeated water to obtain mixed water.

Further, the present invention is a water treatment apparatus having: a water pressure-increasing device, a reverse osmosis membrane module for separating the water having been subjected to pressure increase into concentrated water and permeated water, a boron removing device for removing boron from the treated water of the reverse osmosis membrane module, a flow path of water not passing through the boron removing device, and a mixing device for mixing the water having passed through the boron removing device and the water not passing through the boron removing device. Here, the treated water of the reverse osmosis membrane module means water from which solutes such as salts have been removed by the reverse osmosis membrane module.

Drawings

Fig. 1 is a schematic configuration diagram of main components of a water treatment apparatus of the related art.

Fig. 2 to 14 and 17 to 20 are schematic configuration diagrams showing main components of a water treatment apparatus according to an embodiment of the present invention.

Fig. 15 is a partial configuration diagram of a water treatment facility in which a part of the reverse osmosis membrane module 2 in fig. 2 is divided into two stages.

Fig. 16 is a partial configuration diagram of a water treatment apparatus in which a part of the reverse osmosis membrane module 2 in fig. 2 is divided into two stages and is provided with a non-powered compressor.

Detailed Description

The water treatment method and the water treatment apparatus of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 is a schematic configuration diagram showing main components of a water treatment apparatus according to an embodiment of the present invention.

As shown in fig. 2, the water treatment facility of the present invention includes a reverse osmosis membrane module 2. Further, a high-pressure pump 1 (pressure raising device) for raising the pressure of water to supply the water to the reverse osmosis membrane module 2 is provided on the upstream side of the reverse osmosis membrane module 2. The reverse osmosis membrane module 2 can separate the pressurized feed water (a) into concentrated water (C) and permeate water (B). On the downstream side of the reverse osmosis membrane module 2, a boron removal device 3 for removing boron from water and a bypass pipe 7 as a flow path of water not passing through the boron removal device 3 are provided in parallel. On the upstream side of the reverse osmosis membrane module 2, a flow rate regulating valve 4a is preferably provided. The bypass pipe 7 also preferably has a flow rate control valve 4 b.

On the downstream side of the boron removal device 3 and the bypass pipe 7, there is a mixing device for mixing the water that has passed through the boron removal device and the water that has not passed through the boron removal device. Here, the mixing device may be any device that can easily join the flow path of water that has passed through the boron removal device and the flow path of water that has not passed through the boron removal device. A water storage tank (not shown) may be provided at the point of confluence of the flow paths or on the downstream side thereof. From the viewpoint of installation site, it is advantageous that the water storage tank is not provided. On the other hand, the water storage tank is advantageously provided from the viewpoint of easily maintaining the quality of the mixed water constant. The water having undergone the boron removal treatment is mixed with the water of the permeated water (B) which has not undergone the boron removal treatment by a mixing device to obtain mixed water (D).

As the boron removal device 3, a device for removing boron with an adsorbent can be used. Although there is a method of removing boron by alkaline coagulation and precipitation by aluminum salt and slaked lime, this method is only suitable for a case where the boron concentration is high, and the cost is increased when a large amount of a dilute solution is to be treated. Therefore, in the case of treating seawater or the like, a method of removing boron by an adsorbent is preferable. As the adsorbent, an inorganic adsorbent, an ion exchange resin, a chelate resin, or the like can be used, but a chelate resin having a very high selectivity for boron is preferable.

In the present invention, the reverse osmosis membrane usable in the reverse osmosis membrane module 2 is a semipermeable membrane that allows only a part of the feed water, for example, water, to permeate therethrough and does not allow other components to permeate therethrough. As a raw material of the reverse osmosis membrane, a polymer material such as a cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer, or the like can be used. The structure of the membrane includes an asymmetric membrane structure having a dense layer on at least one surface of the membrane and micropores having pore diameters gradually increasing from the dense layer toward the inside of the membrane or toward the other surface of the membrane, a composite membrane structure having a very thin separation function layer made of another material on the dense layer of the asymmetric membrane, and the like. According to the membrane form, there are hollow fiber membranes and flat membranes. The present invention can be used regardless of the raw material of the film, the structure of the film, or the form of the film, and is effective in any case, but typical examples of the film include an asymmetric film of cellulose acetate or polyamide, and a composite film having a separation function layer of polyamide or polyurea. From the viewpoint of water treatment amount, durability, and salt removal rate, cellulose acetate-based asymmetric membranes or polyamide-based composite membranes are preferably used.

In order to put such a membrane into practical use, it may be assembled into an element such as a spiral, a tubular, a flat plate, or a frame, or in the case of a hollow fiber membrane, it may be assembled into an element after being gathered into a bundle and used.

The reverse osmosis membrane module can be prepared by housing the membrane elements described above in 1 to a plurality of pressure vessels. Such an assembly may also be used in a multiple parallel configuration. The combination, number and arrangement of the components can be arbitrarily made according to the purpose.

The flow direction of water in the above water treatment facility will be described below in the case of using seawater as raw water. Seawater (raw water) subjected to a pretreatment such as sterilization or removal of a turbid component is pressurized by a high-pressure pump 1 and supplied to a reverse osmosis membrane module 2. The supplied seawater is separated into permeate from which solutes such as salts have been removed and concentrate from which solutes such as salts have been concentrated, and the concentrate is discharged from a discharge port.

The permeated water (fresh water) obtained by the reverse osmosis membrane module 2 is distributed into water flowing into the boron removal device 3 and water passing through the bypass 7 at a branching point between the boron removal device 3 and the bypass 7. The water flowing into the boron removal device 3 is mixed with the water passing through the bypass pipe 7 at the point of confluence of the flow paths after boron is removed by the adsorbent. Thus, mixed water adjusted to a desired boron concentration can be obtained.

In this apparatus, it is preferable to have a control means (not shown in the figure) for controlling the flow ratio of water passing through the boron removal means 3 to water passing through the bypass pipe 7. Therefore, it is preferable to obtain mixed water of a desired water quality by controlling the flow ratio of water to which boron removal treatment is applied to water to which boron removal treatment is not applied. The control device preferably has a permeated water amount sensor (not shown) and a boron concentration sensor (not shown). For example, a permeated water amount sensor and a boron concentration sensor may be provided between the reverse osmosis module 2 and a branching point between the boron removal device 3 and the bypass pipe 7, and further, a boron concentration sensor may be provided downstream of a merging point between a flow path of water passing through the boron removal device 3 and the bypass pipe. Thus, the flow ratio of the water flowing into the boron removal device 3 and the water passing through the bypass pipe can be determined and adjusted according to the boron concentration of the permeate water of the reverse osmosis membrane module 2, the boron concentration of the mixed water, and the amount of permeate water obtained by the reverse osmosis membrane module 2.

Specifically, the permeate flow rate measured by the permeate flow rate sensor provided on the permeate side of the reverse osmosis membrane module 2, the boron concentration in the permeate measured by the boron concentration sensor, and the boron concentration in the mixed water measured by the boron concentration sensor provided downstream of the bypass pipe and the confluence point of the permeate having passed through the boron removal device 3 are inputted to the adjusting device as information indicating the operation state of the water treatment facility. The adjusting device is configured to adjust the flow rate control valve 4a and the flow rate control valve 4b based on the measurement data. The regulating device is composed of a permeated water quality control part, a permeated water quantity control part, a bypass water quantity control part and the like.

That is, in the case where the permeated water obtained by the reverse osmosis membrane module 2 is poor in quality, that is, in the case where the boron concentration of the permeated water is 0.5mg/L or more defined as the WHO water quality index value, the flow control valves 4a and 4b are controlled so that a part of the permeated water flows to the boron removal device 3 side and the remaining part flows to the bypass pipe 7 side. The proportion of the water flowing to the bypass pipe 7 side is not limited as long as the boron concentration in the mixed water can be controlled to 0.5mg/L or less than 0.5 mg/L. When the quality of the permeated water obtained by the reverse osmosis membrane module 2 is excellent, that is, when the boron concentration of the permeated water is 0.5mg/L or less than 0.5mg/L, the flow control valve 4a is closed and the flow control valve 4b is fully opened so that the whole of the permeated water does not flow to the boron removal device side but flows into the bypass pipe 7 side.

Thus, by controlling the flow rate ratio of the permeated water passing through the boron removal device to the permeated water passing through the bypass pipe device according to the difference in water quality, even in the case of raw water having a changed water quality due to a change in temperature of seawater or the like, treated water having a stable boron concentration can be constantly obtained. In addition, the boron removal apparatus can be utilized more efficiently, so that the economy can be further improved. The flow rate ratio may be adjusted by time-sharing control for controlling the opening/closing time of the flow rate control valves 4a and 4 b.

Thus, according to the present invention, drinking water from which boron has been removed can be obtained from raw water having a boron concentration of 3mg/L or more, such as sea water or salt water. Moreover, the boron removal device can be efficiently utilized, and the equipment cost and the running cost can be reduced, thereby improving the economy.

Further, by using an adsorbent that selectively adsorbs only boron, only boron can be removed from water without removing mineral components. Therefore, water containing a proper amount of mineral components and having a good taste can be obtained.

Fig. 3 is a schematic diagram showing the main components of a water treatment apparatus according to another embodiment of the present invention. In this embodiment, the reverse osmosis membrane module 2 is composed of a plurality of reverse osmosis membrane modules 2(a) and 2 (b). The permeate water side of the reverse osmosis membrane module 2(b) is connected to a boron removal device 3. On the other hand, the permeate side of the reverse osmosis membrane module 2(a) is joined to the flow path passing through the boron removal device 3 via the flow path not passing through the boron removal device 3.

FIG. 4 is a schematic configuration diagram showing the main components of a water treatment apparatus according to another embodiment of the present invention. In this embodiment, the reverse osmosis membrane module 2 is used as the 1 st reverse osmosis membrane module, and the 2 nd reverse osmosis membrane module 6 is provided downstream of the water-permeable side thereof. In this case, a low-pressure pump 5 (pressure raising device) is provided between the 1 st reverse osmosis membrane module 2 and the 2 nd reverse osmosis membrane module 6. The water pressurized by the low-pressure pump 5 is further separated into concentrated water and permeated water in the 2 nd reverse osmosis membrane module 6.

Then, a boron removal device 3 is provided downstream of the 2 nd reverse osmosis membrane module 6 on the side of the concentrated water, and boron is removed by passing at least a part of the concentrated water through the boron removal device 3. The entire amount of the concentrated water may be passed through the boron removal device 3. By providing a pipe or the like for joining the concentrated water of the 2 nd reverse osmosis membrane module 6 from which boron is removed and the permeated water of the 2 nd reverse osmosis membrane module 6, it is possible to mix the water that has not passed through the boron removal device 3 and the water that has passed through the boron removal device 3.

Although not shown in the figure, an alkali injection device for adjusting the pH of water is preferably provided between the 1 st reverse osmosis membrane module 2 and the 2 nd reverse osmosis membrane module 6. Either one of the alkali injection device and the low-pressure pump (pressure boosting device) may be provided on the upstream side. When the alkali injection device is provided upstream of the 1 st reverse osmosis membrane module 2, it is not preferable because scale is easily generated because alkali is injected into water having a high ion concentration.

The seawater pressurized by the high pressure pump 1 and supplied to the 1 st reverse osmosis membrane module 2 is separated into permeate from which solutes such as salts are removed and concentrate from which the solutes such as salts are concentrated, and the concentrate is discharged from a discharge port. Then, the permeated water (fresh water) obtained by the reverse osmosis membrane module 2 is adjusted in pH by the alkali injection device, so that boric acid contained in the water is dissociated into anions. The dissociation constant pKa of boric acid is 9, and almost non-dissociated in seawater. However, the composite reverse osmosis membrane having a separation functional layer of crosslinked wholly aromatic polyamide, which is a representative permeable membrane, has a performance of being capable of removing ionic substances better than neutral substances. Therefore, the pH is preferably adjusted to 9 or more. The pH is more preferably 9.5 or more and 11 or less. As the alkali, it is preferable to use a concentrated aqueous solution of an alkaline salt such as sodium hydroxide or sodium carbonate, and inject it by a chemical injection pump.

The permeate of the 1 st reverse osmosis membrane module 2, which has been adjusted to a pH value suitable for boron removal, is pressurized by the low-pressure pump 5 and supplied to the 2 nd osmosis membrane module 6, where it is further separated into permeate from which boron and the like have been removed and concentrate from which boron and the like have been concentrated.

Then, at least a part of the concentrated water of the reverse osmosis membrane module 6 is sent to the boron removal device 3 where boron is removed, and then mixed with the permeate water of the 2 nd reverse osmosis membrane module 6.

In this embodiment, by treating water that has been adjusted to a pH value suitable for boron removal using the 2 nd reverse osmosis membrane module 6, for example, on the permeate water side, water from which boron is removed can be obtained in a proportion equivalent to about 90% of the feed water, while on the concentrate water side, a small amount of boron-concentrated water equivalent to about 10% of the feed water can be obtained. Since only a small amount of the concentrated water is treated by the boron removal apparatus containing the adsorbent, boron can be removed efficiently, which is economically advantageous. The water from which boron has been removed is then mixed with the permeate water of the reverse osmosis membrane module 6, so that the water treatment efficiency can be improved. For example, the water treatment efficiency of the boron removal step can reach high efficiency of 99% or more than 99%. Boron is removed by a reverse osmosis membrane method known in the past, and since concentrated water is discharged, it is difficult to achieve water treatment efficiency of 90% or more.

In addition, when boron is removed by a conventionally known reverse osmosis membrane method, mineral components such as calcium and magnesium contained in water are discharged together with concentrated water, and thus the water becomes unpalatable when used as drinking water. In the water treatment facility of the present embodiment, since the adsorbent capable of selectively adsorbing only boron is used, only boron can be removed from the concentrated water of the reverse osmosis membrane module 6 without removing mineral components. By mixing the obtained water with the permeated water, calcium and magnesium which have been removed in the reverse osmosis membrane module 6 can be returned to the permeated water, and thus water having a good taste and containing a proper amount of mineral components can be obtained.

In this embodiment, the membranes used in the 1 st reverse osmosis membrane module 2 are preferably those having a desalting rate of 90% or more when a saline solution having a concentration of 35 mg/L and 700mg/L at 25 ℃ and pH6.5 is supplied at a pressure of 5.5 MPa. The higher the desalting rate is, the lower the chloride ion concentration in the permeated water is, and therefore the better the membrane is, and the membrane having the separation performance with the desalting rate of 95% or more, particularly 99% or more, is more preferable. If the desalination rate is less than 90%, the amount of chloride ions in the permeate increases, and it is difficult to use the permeate as drinking water or industrial water as it is.

In the present invention, the membrane used in the 2 nd reverse osmosis membrane module 6 is preferably a membrane having a permeation flow rate of 0.8m when a saline solution having a concentration of 1500mg/L and a pH of 6.5 at 25 ℃ is supplied at a pressure of 1.5MPa³/m²Day or 0.8m³/m²Films with performance over days. In addition, in order to ensure a larger flow rate per unit cell, the permeate flow rate is more preferably 1.0m³/m²Day or 1.0m³/m²Day or more. When the saline solution having a concentration of 1,500mg/L and a temperature of 25 ℃ and pH6.5 is supplied at a pressure of 1.5MPa, the membrane preferably has a separation performance of a desalting rate of 90% or more, more preferably 98% or more, and when the magnesium sulfate aqueous solution having a concentration of 1500mg/L and a temperature of 25 ℃ and pH6.5 is supplied at a pressure of 1.5MPa, the membrane preferably has a separation performance of a desalting rate of 90% or more, more preferably 98% or more.

In the present invention, in the case where a plurality of reverse osmosis membrane modules are provided, any arrangement may be used as long as it is configured such that water having passed through the boron removal means is mixed with water having not passed through the boron removal means, and the number of stages may be 3, 4 or more stages. Fig. 5 to 14 show various embodiments.

Fig. 5 is a schematic configuration diagram of main components of a water treatment apparatus in which a 2 nd reverse osmosis membrane module is provided in a bypass pipe of fig. 2. Fig. 6 is a schematic configuration diagram of main components of a water treatment apparatus in which a reverse osmosis membrane module portion in fig. 5 is changed to a plurality of stages. FIG. 7 is a schematic configuration diagram of main parts of a water treatment apparatus provided with a No. 2 reverse osmosis membrane module before the boron removal device of FIG. 2. Fig. 8 is a schematic configuration diagram of main components of a water treatment apparatus in which a reverse osmosis membrane module portion in fig. 7 is changed to a plurality of stages. Fig. 9 is a schematic configuration diagram of main components of a water treatment apparatus in which a 2 nd reverse osmosis membrane module is provided before a branch point of a bypass pipe of fig. 2. Fig. 10 is a schematic configuration diagram of main components of a water treatment facility in which a reverse osmosis membrane module portion of fig. 4 is changed to a plurality of stages. Fig. 11 is a schematic configuration diagram of main components of a water treatment facility in which a reverse osmosis membrane module portion of fig. 4 is changed to a multistage. Fig. 12 is a schematic configuration diagram of main parts of a water treatment apparatus in which a reverse osmosis membrane module is provided before the reverse osmosis membrane module of fig. 4, and the reverse osmosis membrane module portion of fig. 4 is changed into a plurality of stages. Fig. 13 is a schematic configuration diagram of main parts of a water treatment apparatus in which a reverse osmosis membrane module in fig. 4 is partially changed into a plurality of stages and a part of the concentrated water is treated at a subsequent stage. Fig. 14 is a schematic configuration diagram of main components of a water treatment apparatus in which a reverse osmosis membrane module portion in fig. 4 is changed to a plurality of stages.

In all the figures, it is preferable to provide an alkali injection device for adjusting the pH of water between the 1 st reverse osmosis membrane module 2 and the 2 nd reverse osmosis membrane module 6.

The reverse osmosis membrane modules 2 and 6 shown in fig. 2 to 14 may be each configured as shown in fig. 15 by being divided into 2 stages, and the concentrated water obtained in the reverse osmosis membrane module 2x of the 1 st stage may be pressurized by the pump 1y and then supplied to the reverse osmosis membrane module 2y of the 2 nd stage. By flowing the permeated water obtained in the reverse osmosis membrane module 2y of the 2 nd stage together with the permeated water obtained in the reverse osmosis membrane module 2x of the 1 st stage, the water treatment efficiency can be improved. In this case, as shown in fig. 16, a compressor 1z such as a turbocharger that operates by recovering energy of the concentrated water discharged from the reverse osmosis membrane module 2y of the 2 nd stage may be used as a pump for supplying the concentrated water of the 1 st stage to the reverse osmosis membrane module 2y of the 2 nd stage, and thus the cost of water treatment may be reduced.

In addition, when the pretreatment for supplying seawater (raw water) is performed by filtration using a membrane such as an MF membrane or a UF membrane, since the turbidity component of the feed water is reduced, the feed water can be supplied to the reverse osmosis membrane module 2 at a high flow rate, and thus a pump or an energy recovery device between the reverse osmosis membrane modules of the 1 st and 2 nd stages is not required.

In all of fig. 4 to 14, it is preferable that the concentrated water obtained in the 2 nd reverse osmosis membrane module is returned to the supply side of the 1 st reverse osmosis membrane module. Since the concentrated water obtained in the 2 nd reverse osmosis membrane module has a high boron concentration and also has a good water quality, the cost for water treatment can be reduced by returning the concentrated water to the supply side again for use.

FIG. 17 is a schematic configuration diagram showing main components of a water treatment apparatus according to another embodiment of the present invention. In this embodiment, the 1 st reverse osmosis membrane module 2 is constituted by two stages, and the concentrate side of the reverse osmosis membrane module 2x of the 1 st stage is connected to the reverse osmosis membrane module 2y of the 2 nd stage. Then, downstream of the permeate water side of the reverse osmosis membrane module 2y of the 2 nd stage, the boron removal device 3 and the bypass pipe 7 as a flow path of water not passing through the boron removal device 3 are provided in parallel. Then, the water that has passed through the boron removal device 3 is mixed with the water that has not passed through the boron removal device 3.

FIG. 18 is a schematic configuration diagram showing main components of a water treatment apparatus according to another embodiment of the present invention. In this embodiment, the 1 st reverse osmosis membrane module 2 is constituted by two stages, and the concentrate side of the reverse osmosis membrane module 2x of the 1 st stage is connected to the permeable membrane module 2y of the 2 nd stage. Then, a low-pressure pump 5 (pressure raising device) and a 2 nd reverse osmosis membrane module 6 are provided downstream of the permeate side of the 2 nd reverse osmosis membrane module 2y, and the permeate of the 2 nd reverse osmosis membrane module 2y is separated into concentrated water and permeate water by the 2 nd reverse osmosis membrane module 6. Then, a boron removal device 3 is provided downstream of the concentrated water side of the reverse osmosis membrane module 6, where at least a part of the concentrated water obtained in the reverse osmosis membrane module 6 is removed of boron therein. Then, the concentrated water of the reverse osmosis membrane module 6 from which boron has been removed is mixed with the permeate water of the reverse osmosis membrane module 2x and the permeate water of the reverse osmosis membrane module 6.

As shown in fig. 19 and 20, the pump in fig. 17 and 18 is a compressor 1z such as a turbocharger that operates by recovering energy of the concentrated water discharged from the reverse osmosis membrane module 2y of the 2 nd stage, so that the cost of water treatment can be reduced.

Example 1

First, in the pretreatment section, sea water having a salt concentration of 35,700mg/L and a boron concentration of 5mg/L was adjusted to 25 ℃ and pH6.5, and then filtered through a hollow fiber ultrafiltration membrane module. The pretreated water was then introduced into the apparatus shown in FIG. 2, and the pressure was increased to 5.5MPa with the high-pressure pump 1 to supply it to the reverse osmosis membrane module 2. The water treatment efficiency in the reverse osmosis membrane module 2 was 40%, that is, the amount of permeated water of the reverse osmosis membrane module 2 was 40 when the amount of supplied water was taken as 100.

In the following, the water amount is a ratio when the amount of supplied water after the previous treatment is 100, and is indicated by a number in parentheses.

The reverse osmosis membrane module 2 has a TDS (dissolved solids) concentration of the permeate (40) of 150mg/L and a boron concentration of 1.2 mg/L. On the other hand, the TDS concentration of the concentrate (60) of the reverse osmosis membrane module 2 was 60,600mg/L, and the boron concentration was 8 mg/L.

In the permeate water (40) of the reverse osmosis membrane module 2, 40% of the water (16) flows through the bypass pipe 7. The remaining 60% of the water (24) flows through the adsorption column 3 packed with the chelate resin, where boron is removed. When the water for resin regeneration is removed, the amount of water passing through the adsorption column is (23). The boron concentration in the water after passing through the adsorption column was 0.05 mg/L. Since TDS is not removed by the chelate resin, the TDS concentration in the water after passing through the adsorption column was 150mg/L as before passing through the adsorption column. Then, by mixing the water (23) treated by the adsorption tower 3 with the water (16) passing through the bypass pipe 7, mixed water (39) can be obtained. The TDS concentration of the mixed water was 150mg/L, and the boron concentration was 0.5 mg/L. The water treatment efficiency after the reverse osmosis membrane module 2 was 98%.

Comparative example 1

On the other hand, in contrast to example 1 described above, in the case where the bypass pipe 7 is not provided and the entire amount of the permeated water (40) of the reverse osmosis membrane module 2 is passed through the adsorption tower 3, the water treatment efficiency after the reverse osmosis membrane module 2 is reduced to 96%. The boron concentration became 0.05mg/L, that is, boron was excessively removed. Therefore, the amount of the resin packed in the adsorption column must be increased as compared with example 1.

In comparison of the resin amounts in example 1 and comparative example 1, the resin amount in the adsorption column of example 1 is only required to be 60 if the resin amount in the adsorption column of comparative example 1 is 100. That is, the amount of resin in the adsorption column can be reduced by 40% by using the water treatment method and the water treatment apparatus of the present invention. This reduces the initial installation costs of the apparatus and even the water treatment costs.

Example 2

The pretreated water was introduced into the apparatus shown in FIG. 4 in the same manner as in example 1. The pretreated water was pressurized to 5.5MPa by the high-pressure pump 1 and then supplied to the 1 st reverse osmosis membrane module 2. In the 1 st reverse osmosis membrane module 2, the water treatment efficiency is 40%, that is, when the feed water amount is taken as 100, the permeated water amount of the reverse osmosis membrane module 2 is 40.

The membrane used in the reverse osmosis membrane module 1, 2, was a membrane having a desalting rate of 99.6% when a saline solution having a concentration of 35,700mg/L and a pH of 6.5.5 at 25 ℃ was supplied thereto under a pressure of 5.5 MPa.

In the same manner as in example 1, the TDS (dissolved solids) concentration of the permeate (40) of the 1 st reverse osmosis membrane module 2 was 150mg/L, and the boron concentration was 1.2 mg/L. The TDS concentration of the concentrated water (60) of the 1 st reverse osmosis membrane module 2 is 60,600mg/L, and the boron concentration is 8 mg/L.

The permeate (40) obtained in the 1 st reverse osmosis membrane module 2 is adjusted to a pH value of 10 using an alkali injection device and then fed into the 2 nd reverse osmosis membrane module 6 using a low-pressure pump 5. In the 2 nd reverse osmosis membrane module 6, the water treatment efficiency was 90%. The pressure of the low-pressure pump is 1 MPa.

For 2 nd reactionThe membrane used in the permeable membrane module 6 is a membrane having a permeation flow rate of 0.8m when a saline solution having a concentration of 1500mg/L and a pH of 6.5 at 25 ℃ is supplied thereto under a pressure of 1.5MPa³/m²Day or 0.8m³/m²Day or more.

The TDS concentration of the permeated water (36) of the 2 nd reverse osmosis membrane assembly 6 is 3mg/L, and the boron concentration is 0.24 mg/L. The TDS concentration of the concentrated water (4) was 1,100mg/L, and the boron concentration was 8 mg/L. The concentrated water (4) is passed into an adsorption column 3 filled with a chelate resin to remove boron therefrom. When the water for resin regeneration was removed, the amount of water passing through the adsorption column was (3.8). The TDS concentration of the water after boron removal is 1,100mg/L, and the boron concentration is 0.05 mg/L. Then, by mixing the water (3.8) treated by the adsorption tower 3 with the permeated water (36) of the 2 nd reverse osmosis membrane module 6, mixed water (39.8) is obtained. The TDS concentration of the mixed water was 150mg/L, and the boron concentration was 0.23 mg/L. The water treatment efficiency after the 2 nd reverse osmosis membrane module 6 reaches 99.5 percent.

The water having good taste for drinking preferably contains a proper amount (30 to 200mg/L) of mineral components such as calcium and magnesium. The mixed water obtained in example 2 had a TDS concentration of 150mg/L, contained appropriate amounts of calcium and magnesium, and was considered to be most suitable as drinking water.

In addition, since only the concentrate (4) passing through the second reverse osmosis membrane module 6 is required for the amount of the resin in the adsorption column 3, a very small amount of the resin is required.

Comparative example 2

On the other hand, in contrast to example 2, when the boron removal device 3 was not provided on the concentrated water side of the 2 nd reverse osmosis membrane module 6 and the concentrated water was discharged, the water treatment efficiency after the 2 nd reverse osmosis membrane module 6 was 90%. The water treatment amount was (36) relative to the supply water amount after pretreatment (100). In order to obtain the same amount of boron-removed water as in example 2, the supply water after pretreatment had to reach (111), and the pretreatment equipment cost and the equipment cost related to the 1 st reverse osmosis membrane module became useless costs. In addition, electricity costs are required, and water treatment costs are increased.

Further, regarding the water quality, the TDS concentration was 3mg/L and the boron concentration was 0.24 mg/L. Does not contain a proper amount (30-200 mg/L) of mineral components, and thus cannot be said to be water with good mouthfeel.

Industrial applicability

In this way, by separating the boron-containing water using the reverse osmosis membrane module, applying boron removal treatment to a part of the permeate water thus obtained, and then mixing the permeate water subjected to boron removal treatment with the permeate water to which boron removal treatment has not been applied, it is not necessary to remove boron from the raw water to an extent more than necessary, so that the boron removal apparatus can be efficiently utilized, and the facility cost and transportation cost can be reduced. Thus, the economy of water treatment can be improved.

Further, by using at least two reverse osmosis membrane modules, treating the water containing boron with the 1 st reverse osmosis membrane module, separating it into concentrated water and permeated water, adjusting at least a part of the obtained permeated water to a pH value suitable for boron removal, treating with the 2 nd reverse osmosis membrane module, separating it into concentrated water and permeated water, and further subjecting at least a part of the concentrated water obtained in the 2 nd reverse osmosis membrane module to boron removal treatment, efficiency and economy can be further improved.

In the case where the flow rate ratio of the permeated water passing through the boron removal device to the permeated water passing through the bypass device is controlled in accordance with the quality of the permeated water in the reverse osmosis membrane module, it is certainly possible to ensure that the boron concentration of the mixed water is equal to or lower than a predetermined water quality standard, but even in the case of raw water whose quality changes with a temperature change of seawater or the like, treated water having a stable boron concentration can be constantly obtained, and in addition, the boron removal device can be utilized more effectively, and the transportation cost and the water treatment cost can be further reduced, and the economy can be further improved.

In addition, by using an adsorbent that selectively adsorbs only boron, only boron can be removed from water without removing mineral components. Therefore, water containing a proper amount of mineral components and having good taste can be obtained.

Claims (15)

1. A water treatment method comprising a step of separating water containing boron by a reverse osmosis membrane module to obtain permeated water and a step of subjecting a part of the obtained permeated water to a boron removal treatment by an adsorbent, wherein the water subjected to the boron removal treatment is mixed with water not subjected to the boron removal treatment in the permeated water to obtain mixed water, characterized in that at least two reverse osmosis membrane modules are used, and the permeated water subjected to the boron removal treatment is concentrated water obtained by a 1 st reverse osmosis membrane module or a 2 nd reverse osmosis membrane module,

the method also comprises a step of treating at least a part of the permeate water obtained by the 1 st reverse osmosis membrane module with a 2 nd reverse osmosis membrane module, and a step of subjecting at least a part of the concentrate water obtained by the 2 nd reverse osmosis membrane module to a boron removal treatment; alternatively, the method comprises a step of treating at least a part of the concentrated water obtained in the 1 st reverse osmosis membrane module with a 2 nd reverse osmosis membrane module, and a step of subjecting at least a part of the permeated water obtained by the 2 nd reverse osmosis membrane module to a boron removal treatment.

2. The water treatment method as claimed in claim 1, which has a step of treating at least a part of the permeated water obtained in the 1 st reverse osmosis membrane module with a 2 nd reverse osmosis membrane module, and a boron removal treatment is applied to at least a part of the concentrated water obtained by the 2 nd reverse osmosis membrane module.

3. The method of treating water according to claim 2, wherein a reverse osmosis membrane having a desalting rate of 90% or more when a salt solution having a concentration of 35700mg/L and a pH of 6.5 at 25 ℃ is supplied at a pressure of 5.5MPa is used in the 1 st reverse osmosis membrane module; and a reverse osmosis membrane module 2 using a reverse osmosis membrane having a permeation flow rate of 0.8m when a saline solution having a concentration of 1500mg/L and a pH of 6.5 at 25 ℃ is supplied at a pressure of 1.5MPa³/m²Day or 0.8m³/m²Day or more.

4. The water treatment method as claimed in claim 2, wherein the feed side pH of the 2 nd reverse osmosis membrane module is 9 or more.

5. The water treatment method as claimed in claim 1, which has a step of treating at least a part of the concentrated water obtained in the 1 st reverse osmosis membrane module with a 2 nd reverse osmosis membrane module, and a step of subjecting at least a part of the permeated water obtained by the 2 nd reverse osmosis membrane module to a boron removal treatment.

6. The water treatment method as claimed in claim 1, wherein the mixed water of a desired water quality is obtained by controlling a flow ratio of water subjected to boron removal treatment to water not subjected to boron removal treatment.

7. The water treatment method according to claim 1, wherein raw water having a boron concentration of 3mg/L or more is treated.

8. A water treatment apparatus, the apparatus having: a pressure raising device for water, a reverse osmosis membrane module for separating the water having been subjected to pressure raising into concentrated water and permeated water, a boron removing device using an adsorbent for removing boron from the treated water of the reverse osmosis membrane module, a flow path for water not passing through the boron removing device in the permeated water, and a mixing device for mixing the water passing through the boron removing device and the water not passing through the boron removing device in the permeated water,

the apparatus has at least two reverse osmosis membrane modules,

the 2 nd reverse osmosis membrane module is connected with the permeate side of the 1 st reverse osmosis membrane module, and the boron removal device is connected with the concentrated water side of the 2 nd reverse osmosis membrane module; or the 2 nd reverse osmosis membrane module is connected with the concentrated water side of the 1 st reverse osmosis membrane module, the boron removal device is connected with the permeated water side of the 2 nd reverse osmosis membrane module,

the permeated water passing through the boron removal device is concentrated water obtained by the 1 st reverse osmosis membrane module or the 2 nd reverse osmosis membrane module.

9. The water treatment apparatus as claimed in claim 8, wherein the 2 nd reverse osmosis membrane module is connected to a permeate side of the 1 st reverse osmosis membrane module, and a concentrate side of the 2 nd reverse osmosis membrane module is connected to the boron removal device.

10. The water treatment apparatus as claimed in claim 9, wherein the 1 st reverse osmosis membrane module uses a reverse osmosis membrane having a concentration of 35700mg/L when fed with food at 25 ℃, pH6.5 and a pressure of 5.5MPaWhen the salt water is used, the salt removing rate is 90 percent or more than 90 percent; and the 2 nd reverse osmosis membrane module is a reverse osmosis membrane module having a permeate flow rate of 0.8m when a salt solution having a concentration of 1500mg/L and a temperature of 25 ℃ is supplied at a pressure of 1.5MPa³/m²Day or 0.8m³/m²Day or more.

11. The water treatment apparatus as claimed in claim 9, wherein a pH adjusting means for adjusting the pH value of water is provided between the 1 st reverse osmosis membrane module and the 2 nd reverse osmosis membrane module.

12. The water treatment apparatus according to claim 9, which comprises a 3 rd reverse osmosis membrane module for subjecting the concentrated water of the 2 nd reverse osmosis membrane module to a further reverse osmosis treatment and supplying the concentrated water to the boron removal device.

13. The water treatment apparatus as claimed in claim 8, wherein the 2 nd reverse osmosis membrane module is connected to a concentrate side of the 1 st reverse osmosis membrane module, and the boron removing means is connected to a permeate side of the 2 nd reverse osmosis membrane module.

14. The apparatus according to claim 8, further comprising a control device for controlling a flow ratio of water passing through the boron removal device and water not passing through the boron removal device.

15. The water treatment apparatus as claimed in claim 8, wherein the control means has measuring means for measuring a boron concentration in the water, and adjusting means for adjusting a flow ratio of the water passing through the boron removing means and the water not passing through the boron removing means based on the measured boron concentration.