JP7464969B2 - METHOD AND APPARATUS FOR MEMBRANE TREATMENT OF LIQUID TO BE TREATED - Google Patents

Description

The present invention relates to a method and apparatus for membrane treatment of a liquid to be treated, and more specifically, to a method and apparatus for membrane treatment of a liquid to be treated that utilizes a reverse osmosis membrane.

As a method for treating a liquid to be treated using a reverse osmosis membrane, for example, the fresh water production method disclosed in Patent Document 1 is known. In the fresh water production method of Patent Document 1, seawater is pressurized and supplied to a reverse osmosis membrane module to separate fresh water, and then concentrated saltwater that does not pass through the reverse osmosis membrane is depressurized by energy exchange with seawater and supplied to a forward osmosis membrane module, where the concentrated saltwater is diluted with water that passes through the forward osmosis membrane.

JP 2016-97331 A

The reverse osmosis membrane method requires the application of a pressure higher than the osmotic pressure of the liquid being treated, which limits how highly concentrated it can be. On the other hand, the above-mentioned conventional freshwater production method requires the concentrated saltwater to be diluted with water in the forward osmosis membrane module, which leaves room for improvement in terms of increasing the concentration rate of the liquid being treated.

The present invention aims to provide a membrane treatment method and device for treating a liquid that can efficiently concentrate the liquid to a high concentration.

The object of the present invention is achieved by a membrane treatment method for a liquid to be treated, comprising: a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without permeating the reverse osmosis membrane; and a second concentration step in which the produced concentrated liquid is brought into contact with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentration step comprising a step of contacting the concentrated liquid with the recovery liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid being supplied in series to the semipermeable membrane units of each stage, the recovery liquid being supplied to the semipermeable membrane units of each stage so that at least two of the semipermeable membrane units are in parallel, and at least a portion of the concentrated liquid concentrated in the second concentration step is used as the recovery liquid, and the second concentration step comprises a step of pressurizing the concentrated liquid supplied to the semipermeable membrane unit of the front stage by pressure exchange with the concentrated liquid discharged from the semipermeable membrane unit of the last stage .

The second concentration step may also include a step of merging the recovered liquid discharged from at least one of the semipermeable membrane units in each stage with the recovered liquid supplied to at least one of the semipermeable membrane units in each stage.

Alternatively, the object of the present invention is achieved by a membrane treatment method for a liquid to be treated, which comprises a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without permeating the reverse osmosis membrane, and a second concentration step in which the produced concentrated liquid is brought into contact with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentration step comprising a step of contacting the concentrated liquid with the recovery liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid being supplied in series to the semipermeable membrane units of each stage, and the recovery liquid being supplied to the semipermeable membrane units of each stage so that at least two of the semipermeable membrane units are in parallel, and at least a portion of the concentrated liquid concentrated in the second concentration step is used as the recovery liquid, and the first concentration step comprises a step of passing the liquid to be treated through a nanofiltration membrane before the pressure of the liquid to be treated is increased, and the non-permeated liquid that does not permeate the nanofiltration membrane of the liquid to be treated is merged with at least a portion of the concentrated liquid concentrated in the second concentration step and used as the recovery liquid.

Alternatively, the object of the present invention is achieved by a membrane treatment method for a liquid to be treated, comprising: a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without permeating the reverse osmosis membrane; and a second concentration step in which the produced concentrated liquid is brought into contact with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentration step comprising a step of contacting the concentrated liquid with the recovery liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid being supplied in series to the semipermeable membrane units of each stage, the recovery liquid being supplied to the semipermeable membrane units of each stage so that at least two are in parallel, at least a portion of the concentrated liquid concentrated in the second concentration step is used as the recovery liquid, and the second concentration step comprises combining the recovery liquid supplied in parallel to at least two of the semipermeable membrane units on the latter stage and supplying it to the semipermeable membrane unit on the former stage.

Alternatively, the object of the present invention is achieved by a membrane treatment method for a liquid to be treated, comprising: a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without passing through the reverse osmosis membrane; and a second concentration step in which the produced concentrated liquid is brought into contact with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentration step comprising a step of contacting the concentrated liquid with the recovery liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid is supplied in series to the semipermeable membrane units of each stage, the recovery liquid is supplied to the semipermeable membrane units of each stage so that at least two are in parallel, at least a portion of the concentrated liquid concentrated in the second concentration step is used as the recovery liquid, and the second concentration step comprises supplying the recovery liquid supplied to the semipermeable membrane unit on the latter stage in parallel to at least two semipermeable membrane units on the former stage.

Alternatively, the object of the present invention is achieved by a membrane treatment method for a liquid to be treated, comprising: a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without passing through the reverse osmosis membrane; and a second concentration step in which the produced concentrated liquid is brought into contact with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentration step comprising a step of contacting the concentrated liquid with the recovery liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid being supplied in series to the semipermeable membrane units of each stage, the recovery liquid being supplied to the semipermeable membrane units of each stage so that at least two are in parallel, at least a portion of the concentrated liquid concentrated in the second concentration step is used as the recovery liquid, and the second concentration step comprises combining the recovery liquid supplied in parallel to at least two of the semipermeable membrane units on the latter stage and supplying it in parallel to at least two of the semipermeable membrane units on the former stage.

The object of the present invention is also achieved by a membrane treatment device for a liquid to be treated, which comprises a first concentrating device having an RO membrane unit that generates a concentrated liquid that is concentrated without permeating the reverse osmosis membrane by pressurizing the liquid to be treated and passing it through a reverse osmosis membrane, and a second concentrating device that further concentrates the generated concentrated liquid by contacting it with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentrating device being configured so that the contact between the concentrated liquid and the recovery liquid via the semipermeable membrane is performed in a plurality of stages of semipermeable membrane units, the concentrated liquid is supplied in series to the semipermeable membrane units of each stage, the recovery liquid is supplied to the semipermeable membrane units of each stage so that at least two of the semipermeable membrane units are in parallel, at least a portion of the concentrated liquid concentrated in the second concentrating device is used as the recovery liquid, and the concentrated liquid supplied to the semipermeable membrane unit of the front stage is pressurized by pressure exchange with the concentrated liquid discharged from the semipermeable membrane unit of the last stage .
Alternatively, the object of the present invention is to provide a method for treating a liquid to be treated comprising: a first concentrating device having an RO membrane unit for generating a concentrated liquid that is concentrated without permeating the reverse osmosis membrane by increasing the pressure of the liquid to be treated and passing the liquid through a reverse osmosis membrane; and a second concentrating device for further concentrating the generated concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentrating device being configured so that the contact between the concentrated liquid and the recovery liquid via the semipermeable membrane is performed in a plurality of stages of semipermeable membrane units, the concentrated liquid is supplied in series to the semipermeable membrane units of each stage, The recovery liquid is supplied to the semipermeable membrane units of each stage so that at least two are in parallel, and at least a portion of the concentrated liquid concentrated in the second concentrator is used as the recovery liquid, and the first concentrator further comprises an NF membrane unit having a nanofiltration membrane, and the treated liquid is passed through the nanofiltration membrane before being pressurized, and the non-permeated liquid of the treated liquid that does not permeate the nanofiltration membrane is merged with at least a portion of the concentrated liquid concentrated in the second concentrator, thereby achieving the above-mentioned membrane treatment device for the treated liquid to be used as the recovery liquid.
Alternatively, the object of the present invention is achieved by a membrane treatment device for a liquid to be treated, which comprises a first concentrating device having an RO membrane unit that generates a concentrated liquid that is concentrated without permeating the reverse osmosis membrane by increasing the pressure of the liquid to be treated and passing it through a reverse osmosis membrane, and a second concentrating device that further concentrates the generated concentrated liquid by contacting it with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentrating device being configured to contact the concentrated liquid and the recovery liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid being supplied in series to the semipermeable membrane units of each stage, the recovery liquid being supplied to the semipermeable membrane units of each stage so that at least two of the semipermeable membrane units are in parallel, at least a portion of the concentrated liquid concentrated in the second concentrating device is used as the recovery liquid, and the second concentrating device is configured to combine the recovery liquid supplied in parallel to at least two of the semipermeable membrane units on the rear stage side and supply it to the semipermeable membrane unit on the front stage side.
Alternatively, the object of the present invention is achieved by a membrane treatment device for a liquid to be treated, which includes a first concentrating device having an RO membrane unit that generates a concentrated liquid that is concentrated without permeating the reverse osmosis membrane by increasing the pressure of the liquid to be treated and passing it through a reverse osmosis membrane, and a second concentrating device that further concentrates the generated concentrated liquid by contacting it with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentrating device being configured to contact the concentrated liquid with the recovery liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid being supplied in series to the semipermeable membrane units of each stage, the recovery liquid being supplied to the semipermeable membrane units of each stage so that at least two of the semipermeable membrane units are in parallel, and at least a portion of the concentrated liquid concentrated in the second concentrating device is used as the recovery liquid, and the second concentrating device supplies the recovery liquid supplied to the semipermeable membrane unit on the rear stage to at least two semipermeable membrane units on the front stage in parallel.
Alternatively, the object of the present invention is achieved by a membrane treatment device for a liquid to be treated, which includes a first concentrating device having an RO membrane unit that generates a concentrated liquid that is concentrated without permeating the reverse osmosis membrane by increasing the pressure of the liquid to be treated and passing it through a reverse osmosis membrane, and a second concentrating device that further concentrates the generated concentrated liquid by contacting it with a recovery liquid at a lower pressure than the concentrated liquid via a semipermeable membrane, the second concentrating device being configured to contact the concentrated liquid and the recovery liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid being supplied in series to the semipermeable membrane units of each stage, the recovery liquid being supplied to the semipermeable membrane units of each stage so that at least two of the semipermeable membrane units are in parallel, and at least a portion of the concentrated liquid concentrated in the second concentrating device is used as the recovery liquid, and the second concentrating device combines the recovery liquid supplied in parallel to at least two of the semipermeable membrane units on the rear stage side and supplies it in parallel to at least two of the semipermeable membrane units on the front stage side.

The present invention provides a membrane treatment method and device for treating a liquid that can efficiently concentrate the liquid to a high concentration.

1 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to an embodiment of the present invention. FIG. 11 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to another embodiment of the present invention. FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention. FIG. 13 is a schematic configuration diagram of a membrane treatment device for a liquid to be treated according to still another embodiment of the present invention.

One embodiment of the present invention will be described below with reference to the attached drawings. FIG. 1 is a schematic diagram of a membrane treatment device for a liquid to be treated (hereinafter, simply referred to as a "membrane treatment device") according to one embodiment of the present invention. As shown in FIG. 1, the membrane treatment device 1 mainly comprises a first concentrator 10 that concentrates the liquid to be treated to produce a concentrated liquid, a second concentrator 20 that further concentrates the concentrated liquid produced by the first concentrator 10, and an energy recovery device 30 that performs pressure exchange between the concentrated liquid supplied to the second concentrator 20 and the concentrated liquid discharged from the second concentrator 20.

The first concentrator 10 includes an RO membrane unit 12 configured by arranging an RO membrane (reverse osmosis membrane) module in a casing, and the liquid to be treated that does not permeate the RO membrane is discharged as a concentrated liquid. The first concentrator 10 may be configured with a plurality of RO membrane units 12 arranged in stages, and the liquid to be treated concentrated in the RO membrane unit 12 in the first stage is supplied to the RO membrane unit 12 in the second stage for further concentration to produce a concentrated liquid. The material and type of the RO membrane are not particularly limited, and examples thereof include a hollow fiber membrane type or a flat membrane type made of polyamide, cellulose acetate, or the like.

The second concentrator 20 is equipped with two stages of semipermeable membrane units 21-1 and 21-2. The inside of the casing of each semipermeable membrane unit 21-1 and 21-2 is partitioned by a semipermeable membrane to form a high-pressure chamber 22 and a low-pressure chamber 23. The high-pressure chamber 22 and the low-pressure chamber 23 are configured so that the concentrated liquid and the recovered liquid are supplied from the inlet, respectively, and come into contact with each other via the semipermeable membrane while being discharged from the outlet. The semipermeable membrane may be a hollow fiber membrane other than a flat membrane. The semipermeable membrane may preferably be an FO membrane (forward osmosis membrane), but may also be another semipermeable membrane such as an RO membrane. The concentrated liquid is supplied in series to the high-pressure chamber 22 of each semipermeable membrane unit 21-1 and 21-2, while the recovered liquid is supplied in parallel to the low-pressure chamber 23 of each semipermeable membrane unit 21-1 and 21-2.

The energy recovery device 30 is composed of a turbocharger, and rotates a turbine using the concentrated liquid discharged from the semipermeable membrane unit 21-2 in the final stage of the second concentrator 20, and uses this power to pressurize the concentrated liquid supplied to the semipermeable membrane unit 21-1 in the first stage. The configuration of the energy recovery device 30 is not particularly limited as long as it can recover the energy of the concentrated liquid discharged from the second concentrator 20 and pressurize the concentrated liquid supplied to the second concentrator 20, and for example, it may be a rotor type, piston type, or other energy recovery device other than the turbine type.

Next, a membrane treatment method for a liquid to be treated using the membrane treatment device 1 having the above configuration will be described. First, the liquid to be treated, such as seawater, is pressurized by the high-pressure pump 2 and supplied to the first concentrator 10, thereby carrying out a first concentration step. In the RO membrane unit 12, fresh water is produced by the liquid to be treated passing through the RO membrane, and a concentrated liquid is produced that is concentrated without passing through the RO membrane of the RO membrane unit 12.

Then, the concentrated liquid produced in the first concentration step is boosted by the boost pump 3 and supplied to the second concentration device 20 to perform the second concentration step. The high-pressure concentrated liquid that has been boosted by passing through the first concentration device 10 is supplied in series to the high-pressure chamber 22 of each semipermeable membrane unit 21-1, 21-2. On the other hand, a part of the concentrated liquid after passing through the high-pressure chamber 22 of the semipermeable membrane unit 21-1, 21-2 is supplied in parallel as a recovered liquid after passing through the filter 4 to the low-pressure chamber 23 of each semipermeable membrane unit 21-1, 21-2. This reduces the pressure loss of the low-pressure recovered liquid, and can be reliably supplied to each semipermeable membrane unit 21-1, 21-2, thereby increasing the concentration rate of the treated liquid. The filter 4 is not an essential component, and the configuration may not include the filter 4. The number of stages of the semipermeable membrane units 21-1, 21-2 is not particularly limited as long as it is a plurality of stages, and may be three or more stages. The remainder of the concentrated liquid that is not used as the recovered liquid is discharged outside the system and can be used in other processes, such as forward osmosis power generation and desalination by evaporative concentration for salt production.

The recovery liquid supplied to the low pressure chamber 23 is depressurized by passing through each semipermeable membrane unit 21-1, 21-2, so it is at a lower pressure than the concentrated liquid supplied to the high pressure chamber 22, and the osmotic pressure difference between the concentrated liquid supplied to the high pressure chamber 22 is small, so the pressure difference between the high pressure chamber 22 and the low pressure chamber 23 promotes the movement of water from the high pressure chamber 22 to the low pressure chamber 23 via the semipermeable membrane. Therefore, the concentrated liquid can be further concentrated without particularly increasing the performance or number of the high pressure pumps 2, and can be concentrated to a high concentration with reduced energy. The concentrated liquid concentrated in the second concentrator 20 is depressurized by passing through the energy recovery device 30, and the concentrated liquid supplied to the second concentrator 20 is pressurized, so the pressure difference between the high pressure chamber 22 and the low pressure chamber 23 can be increased.

In the second concentrator 20, water is recovered from the concentrated liquid, and a portion of the recovered liquid discharged from the subsequent semipermeable membrane unit 21-2 is returned by the circulation pump 5 and supplied again in parallel to each semipermeable membrane unit 21-1, 21-2. The remaining recovered liquid is merged with the liquid being treated upstream of the high-pressure pump 2 and supplied again to the first concentrator 10. This increases the efficiency of freshwater production in the first concentrator 10, and the liquid being treated is diluted and its osmotic pressure is reduced, allowing it to be supplied to the RO membrane unit 12 at low pressure, thereby saving energy for the high-pressure pump 2.

Figure 2 is a schematic diagram of a membrane treatment device according to another embodiment of the present invention. The membrane treatment device 101 shown in Figure 2 is the membrane treatment device 1 shown in Figure 1, in which the first concentration device 10 is equipped with an NF membrane unit 14 in addition to the RO membrane unit 12. In Figure 2, components similar to those in Figure 1 are given the same reference numerals (the same applies to Figures 3 to 5 described below).

The NF membrane unit 14 is configured with an NF membrane (nanofiltration membrane) module arranged inside a casing, and the liquid to be treated that has permeated the NF membrane of the NF membrane unit 14 is supplied to the RO membrane unit 12. As with the RO membrane, there are no particular limitations on the material or type of the NF membrane. The NF membrane unit 14 may be configured in multiple stages instead of in one stage.

The second concentrator 20 is equipped with three stages of semipermeable membrane units 21-1, 21-2, and 21-3. The configuration of each semipermeable membrane unit 21-1, 21-2, and 21-3 is the same as that of the semipermeable membrane units 21-1 and 21-2 shown in FIG. 1, and the concentrated liquid is supplied in series from the RO membrane unit 12 to each high-pressure chamber 22, while the recovery liquid, which is a mixture of a part of the concentrated liquid that has passed through the high-pressure chamber 22 and the non-permeated liquid from the NF membrane unit 14, is supplied in parallel to each low-pressure chamber 23 by the operation of the feed water pump 7. Since pressure loss can be reduced by supplying the recovery liquid in parallel to each semipermeable membrane unit 21-1, 21-2, and 21-3, the configuration may not require the provision of a feed water pump 7. The flow rate of the recovery liquid supplied to the low pressure chamber 23 of each semipermeable membrane unit 21-1, 21-2, 21-3 can be individually controlled by adjusting the opening of the flow control valves 40a, 40b, 40c, so that the recovery liquid can be supplied at an appropriate flow rate to each of the semipermeable membrane units 21-1, 21-2, 21-3.

The non-permeated liquid generated in the NF membrane unit 14 has a high osmotic pressure due to an increase in the concentration of solutes, so even if the non-permeated liquid is included in the recovery liquid, the osmotic pressure difference with the concentrated liquid in the second concentrator 20 can be kept small. The recovery liquid only needs to contain the concentrated liquid discharged from the second concentrator 20, and other liquids having a concentration close to that of the concentrated liquid discharged from the second concentrator 20 may be merged together with the non-permeated liquid of the NF membrane unit 14 or instead of the non-permeated liquid of the NF membrane unit 14.

In the energy recovery device 30, the concentrated liquid supplied to the semipermeable membrane unit 21-1 in the front stage is pressurized by the concentrated liquid discharged from the semipermeable membrane unit 21-3 in the last stage. This ensures that the concentrated liquid is supplied to each semipermeable membrane unit 21-1, 21-2, and 21-3, ensuring a pressure difference with the recovered liquid, and promoting concentration in the second concentrator 20.

The recovered liquid discharged from each semipermeable membrane unit 21-1, 21-2, 21-3 is merged and then part of it is circulated individually to each semipermeable membrane unit 21-1, 21-2, 21-3 by the circulation pump 5, thereby diluting the remaining recovered liquid discharged outside the system. The circulation flow rate to each semipermeable membrane unit 21-1, 21-2, 21-3 can be individually controlled by adjusting the opening of the flow control valves 40d, 40e, 40f.

The configuration for circulating the recovery liquid by the circulation pump 5 is not limited to the configuration of this embodiment, and may be any configuration in which the recovery liquid discharged from at least any of the semipermeable membrane units 21-1, 21-2, 21-3 in each stage is merged with the recovery liquid supplied to at least any of the semipermeable membrane units 21-1, 21-2, 21-3 in each stage. Furthermore, circulation of the recovery liquid by the circulation pump 5 is not essential to the present invention, and the recovery liquid may not be circulated.

The membrane treatment device 1, 101 shown in Figures 1 and 2 is configured to supply the recovery liquid to all semipermeable membrane units in parallel in the second concentration step, but it is sufficient that the recovery liquid is supplied to at least two semipermeable membrane units in each stage in parallel. If there is a risk that it will be difficult to control the flow rate of the recovery liquid supplied to each semipermeable membrane unit or to control the concentration difference between the recovery liquid and the concentrated liquid, the recovery liquid may be supplied in series between some of the semipermeable membrane units.

For example, as shown in FIG. 3, in a membrane treatment device 201 equipped with three semipermeable membrane units 21-1, 21-2, and 21-3, the recovery liquid supplied in parallel to the two semipermeable membrane units 21-2 and 21-3 on the rear stage can be merged and supplied to the semipermeable membrane unit 21-1 on the front stage. The merged recovery liquid can be reliably supplied to the semipermeable membrane unit 21-1 by the operation of the booster pump 8, but depending on the pressure of the recovery liquid after merging, the booster pump 8 may not be provided. The number of semipermeable membrane units that supply the recovery liquid in parallel on the rear stage side may be three or more, and a semipermeable membrane unit that supplies the recovery liquid in series may be added to at least some of the semipermeable membrane units arranged in parallel. The number of semipermeable membrane units that are supplied in series on the front stage side may be two or more.

Alternatively, as shown in FIG. 4, in a membrane treatment device 301 equipped with three semipermeable membrane units 21-1, 21-2, and 21-3, the recovery liquid supplied to the semipermeable membrane unit 21-3 on the rear stage can be supplied in parallel to the two semipermeable membrane units 21-1 and 21-2 on the front stage by operating the booster pump 8. The number of semipermeable membrane units that supply the recovery liquid in parallel on the front stage side may be three or more, and a semipermeable membrane unit that supplies the recovery liquid in series may be added to at least some of the semipermeable membrane units arranged in parallel. In addition, the number of semipermeable membrane units that are supplied in series on the rear stage side may be two or more. The membrane treatment device 301 shown in FIG. 4 can also be configured without the booster pump 8.

Alternatively, as shown in FIG. 5, in a membrane treatment device 401 equipped with four semipermeable membrane units 21-1, 21-2, 21-3, and 21-4, the recovery liquid supplied in parallel to the two semipermeable membrane units 21-3 and 21-4 on the rear stage can be merged and supplied in parallel to the two semipermeable membrane units 21-1 and 21-2 on the front stage by operating the booster pump 8. The number of semipermeable membrane units that supply recovery liquid in parallel on the front stage and/or rear stage may be three or more, and a semipermeable membrane unit that supplies recovery liquid in series may be added to at least some of the semipermeable membrane units arranged in parallel. The membrane treatment device 401 shown in FIG. 5 may also be configured without the booster pump 8.

In this way, by appropriately combining parallel supply with serial supply for the supply of recovery liquid to each stage of semipermeable membrane unit in the second concentration step, the concentration and flow rate of the recovery liquid supplied to each semipermeable membrane unit can be easily adjusted. As a result, it is possible to reduce the number of pumps required and improve pump efficiency by increasing the capacity, and it is also possible to equalize the membrane flux in each semipermeable membrane unit.

In the configurations shown in Figures 3 to 5, as in the configuration shown in Figure 2, a portion of the recovered liquid that has passed through and merged with each of the semipermeable membrane units 21-1, 21-2, and 21-3 can be circulated to each of the semipermeable membrane units 21-1, 21-2, and 21-3 individually, and the circulation flow rate to each of the semipermeable membrane units 21-1, 21-2, and 21-3 can be individually controlled by adjusting the opening degree of the flow control valve. The configuration for circulating the recovered liquid may be one in which the recovered liquid discharged from at least any of the semipermeable membrane units 21-1, 21-2, and 21-3 in each stage is merged with the recovered liquid supplied to at least any of the semipermeable membrane units 21-1, 21-2, and 21-3 in each stage.

Reference Signs List 1 Membrane treatment device 10 First concentrator 12 RO membrane unit 14 NF membrane unit 20 Second concentrator 21 Semipermeable membrane unit 30 Energy recovery device

Claims (11)

a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without permeating the reverse osmosis membrane;
A second concentration step of further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane,
The second concentration step includes a step of contacting the concentrated liquid with the recovered liquid through the semipermeable membrane in a plurality of semipermeable membrane units, supplying the concentrated liquid to the semipermeable membrane units in series in each stage, and supplying the recovered liquid to the semipermeable membrane units in each stage such that at least two of the semipermeable membrane units are in parallel,
At least a part of the concentrated liquid concentrated in the second concentration step is used as the recovered liquid ;
The second concentration step is a membrane treatment method for a liquid to be treated, comprising a step of increasing the pressure of the concentrated liquid supplied to the semipermeable membrane unit in the first stage by pressure exchange with the concentrated liquid discharged from the semipermeable membrane unit in the last stage . 2. The membrane treatment method for a liquid to be treated according to claim 1, wherein the second concentration step comprises a step of merging the recovery liquid discharged from at least any of the semipermeable membrane units in each stage with the recovery liquid supplied to at least any of the semipermeable membrane units in each stage. a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without permeating the reverse osmosis membrane;
A second concentration step of further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane,
The second concentration step includes a step of contacting the concentrated liquid with the recovered liquid through the semipermeable membrane in a plurality of semipermeable membrane units, supplying the concentrated liquid to the semipermeable membrane units in series in each stage, and supplying the recovered liquid to the semipermeable membrane units in each stage such that at least two of the semipermeable membrane units are in parallel,
At least a part of the concentrated liquid concentrated in the second concentration step is used as the recovered liquid;
The first concentration step includes a step of passing the liquid to be treated through a nanofiltration membrane before pressurizing the liquid to be treated, and a non-permeated liquid of the liquid to be treated that does not permeate the nanofiltration membrane is merged with at least a portion of the concentrated liquid concentrated in the second concentration step to be used as the recovered liquid. a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without permeating the reverse osmosis membrane;
A second concentration step of further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane,
The second concentration step includes a step of contacting the concentrated liquid with the recovered liquid through the semipermeable membrane in a plurality of semipermeable membrane units, supplying the concentrated liquid to the semipermeable membrane units in series in each stage, and supplying the recovered liquid to the semipermeable membrane units in each stage such that at least two of the semipermeable membrane units are in parallel,
At least a part of the concentrated liquid concentrated in the second concentration step is used as the recovered liquid;
The second concentration step is a membrane treatment method for a liquid to be treated, in which the recovered liquid supplied in parallel to at least two of the semipermeable membrane units on the rear stage is joined together and supplied to the semipermeable membrane unit on the front stage. a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without permeating the reverse osmosis membrane;
A second concentration step of further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane,
The second concentration step includes a step of contacting the concentrated liquid with the recovered liquid through the semipermeable membrane in a plurality of semipermeable membrane units, supplying the concentrated liquid to the semipermeable membrane units in series in each stage, and supplying the recovered liquid to the semipermeable membrane units in each stage such that at least two of the semipermeable membrane units are in parallel,
At least a part of the concentrated liquid concentrated in the second concentration step is used as the recovered liquid;
The second concentration step is a membrane treatment method for a liquid to be treated, in which the recovered liquid supplied to the semipermeable membrane unit on the rear stage side is supplied in parallel to at least two semipermeable membrane units on the front stage side. a first concentration step in which the liquid to be treated is pressurized and passed through a reverse osmosis membrane to produce a concentrated liquid that is concentrated without permeating the reverse osmosis membrane;
A second concentration step of further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane,
The second concentration step includes a step of contacting the concentrated liquid with the recovered liquid through the semipermeable membrane in a plurality of semipermeable membrane units, supplying the concentrated liquid to the semipermeable membrane units in series in each stage, and supplying the recovered liquid to the semipermeable membrane units in each stage such that at least two of the semipermeable membrane units are in parallel,
At least a part of the concentrated liquid concentrated in the second concentration step is used as the recovered liquid;
The second concentration step is a membrane treatment method for a liquid to be treated , in which the recovery liquid supplied in parallel to at least two of the semipermeable membrane units on the downstream side is joined together and supplied in parallel to at least two of the semipermeable membrane units on the upstream side. a first concentrating device having an RO membrane unit for generating a concentrated liquid by increasing the pressure of the liquid to be treated and passing the liquid through a reverse osmosis membrane without permeating the reverse osmosis membrane;
a second concentrating device for further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane;
The second concentrating device is configured to cause contact between the concentrated liquid and the recovered liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid is supplied to the semipermeable membrane units of each stage in series, and the recovered liquid is supplied to the semipermeable membrane units of each stage such that at least two of the semipermeable membrane units are in parallel,
At least a portion of the concentrated liquid concentrated in the second concentrator is used as the recovered liquid ;
The membrane treatment device for a liquid to be treated further comprises an energy recovery device that increases the pressure of the concentrated liquid supplied to the semipermeable membrane unit in the first stage by pressure exchange with the concentrated liquid discharged from the semipermeable membrane unit in the last stage . a first concentrating device having an RO membrane unit for generating a concentrated liquid by increasing the pressure of the liquid to be treated and passing the liquid through a reverse osmosis membrane without permeating the reverse osmosis membrane;
a second concentrating device for further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane;
The second concentrating device is configured to cause contact between the concentrated liquid and the recovered liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid is supplied to the semipermeable membrane units of each stage in series, and the recovered liquid is supplied to the semipermeable membrane units of each stage such that at least two of the semipermeable membrane units are in parallel,
At least a portion of the concentrated liquid concentrated in the second concentrator is used as the recovered liquid;
The first concentrator further comprises a NF membrane unit having a nanofiltration membrane;
A membrane treatment device for the treated liquid, in which the treated liquid is passed through the nanofiltration membrane before being pressurized, and the non-permeated liquid of the treated liquid that does not permeate the nanofiltration membrane is merged with at least a portion of the concentrated liquid concentrated in the second concentrator, and used as the recovered liquid. a first concentrating device having an RO membrane unit for generating a concentrated liquid by increasing the pressure of the liquid to be treated and passing the liquid through a reverse osmosis membrane without permeating the reverse osmosis membrane;
a second concentrating device for further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane;
The second concentrating device is configured to cause contact between the concentrated liquid and the recovered liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid is supplied to the semipermeable membrane units of each stage in series, and the recovered liquid is supplied to the semipermeable membrane units of each stage such that at least two of the semipermeable membrane units are in parallel,
At least a portion of the concentrated liquid concentrated in the second concentrator is used as the recovered liquid;
The second concentrator is a membrane treatment device for a liquid to be treated, in which the recovered liquid supplied in parallel to at least two of the semipermeable membrane units on the downstream side is joined together and supplied to the semipermeable membrane unit on the upstream side. a first concentrating device having an RO membrane unit that generates a concentrated liquid by increasing the pressure of the liquid to be treated and passing the liquid through a reverse osmosis membrane without permeating the reverse osmosis membrane;
a second concentrating device for further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane;
The second concentrating device is configured to cause contact between the concentrated liquid and the recovered liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid is supplied to the semipermeable membrane units of each stage in series, and the recovered liquid is supplied to the semipermeable membrane units of each stage such that at least two of the semipermeable membrane units are in parallel,
At least a portion of the concentrated liquid concentrated in the second concentrator is used as the recovered liquid;
The second concentrator is a membrane treatment device for a liquid to be treated, which supplies the recovered liquid supplied to the semipermeable membrane unit on the rear stage side in parallel to at least two semipermeable membrane units on the front stage side. a first concentrating device having an RO membrane unit for generating a concentrated liquid by increasing the pressure of the liquid to be treated and passing the liquid through a reverse osmosis membrane without permeating the reverse osmosis membrane;
a second concentrating device for further concentrating the produced concentrated liquid by contacting the concentrated liquid with a recovery liquid having a lower pressure than the concentrated liquid through a semipermeable membrane;
The second concentrating device is configured to cause contact between the concentrated liquid and the recovered liquid via the semipermeable membrane in a plurality of stages of semipermeable membrane units, the concentrated liquid is supplied to the semipermeable membrane units of each stage in series, and the recovered liquid is supplied to the semipermeable membrane units of each stage such that at least two of the semipermeable membrane units are in parallel,
At least a portion of the concentrated liquid concentrated in the second concentrator is used as the recovered liquid;
The second concentrator is a membrane treatment device for a liquid to be treated, which combines the recovery liquid supplied in parallel to at least two of the semipermeable membrane units on the downstream side and supplies the combined liquid in parallel to at least two of the semipermeable membrane units on the upstream side.

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