JP2013086019A - Seawater desalination method and seawater desalination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seawater desalination method with which bio-fouling can be suppressed while obtaining clarified water using biologically treated water and seawater.SOLUTION: In a seawater desalination method, biologically treated water obtained by biologically treating organic wastewater is filtered by means of a first reverse osmosis membrane device to obtain concentrated water, the concentrated water is mixed with seawater as dilution water to obtain mixed water, and the mixed water is filtered by means of a second reverse osmosis membrane device. In the seawater desalination method, a first step and a second step are alternately carried out. In the first step, first concentrated water is obtained by filtering biologically treated water by means of the first reverse osmosis membrane device, first mixed water is obtained by mixing the first concentrated water with seawater, and the first mixed water is filtered by means of the second reverse osmosis membrane device. In the second step, second concentrated water is obtained by filtering biologically treated water by means of the second reverse osmosis membrane device, second mixed water is obtained by mixing the second concentrated water with seawater, and the second mixed water is filtered by means of the first reverse osmosis membrane device.

Description

  The present invention relates to a seawater desalination method and a seawater desalination apparatus, for example, a seawater desalination method and a seawater desalination apparatus that desalinate seawater by filtration using a reverse osmosis membrane device having a reverse osmosis membrane (RO membrane).

  In recent years, rain has fallen locally or in a short time due to global warming, etc., and water resources are unevenly distributed geographically or temporally, and the water retention capacity of mountainous areas has declined due to forestry decline or deforestation. As a result, there is a problem that it is difficult to stably secure water resources.

  In order to secure water resources stably, for example, in seaside areas, seawater desalination methods and seawater desalination apparatuses that obtain fresh water as purified water from seawater by filtration using a reverse osmosis membrane device have been proposed (for example, patents). Reference 1).

  However, in the seawater desalination method and seawater desalination apparatus described in Patent Document 1, it is necessary to pressurize seawater with a pump or the like and feed it to the reverse osmosis membrane apparatus in order to filter the seawater with the reverse osmosis membrane apparatus. There is a problem that the higher the salt concentration of seawater, the more energy (power) is required to pump seawater to the reverse osmosis membrane device.

Accordingly, the biologically treated water obtained by biologically treating the wastewater containing organic matter (hereinafter also referred to as “organic wastewater”) in the biological treatment tank is filtered by the first reverse osmosis membrane device to obtain the first concentrated water. And the first permeated water as purified water, mixed with seawater using the first concentrated water as dilution water to obtain mixed water, and the mixed water is filtered through a second reverse osmosis membrane device to obtain purified water. A seawater desalination method and a seawater desalination apparatus for obtaining permeated water (freshwater) have been proposed (for example, Patent Document 2).
Since the first concentrated water obtained by the first reverse osmosis membrane device has a salt concentration lower than seawater, the mixed water obtained by mixing the first concentrated water with seawater as dilution water also has a salt concentration from seawater. Is low. Therefore, the energy required to pump the mixed water to the reverse osmosis membrane device to obtain a predetermined amount of fresh water as purified water is smaller than the energy required to pump seawater to the reverse osmosis membrane device. Such a seawater desalination method and seawater desalination apparatus have the advantage that energy required for pumping per unit amount of purified water to be obtained can be suppressed.
Moreover, according to the seawater desalination method and seawater desalination apparatus, the first permeated water obtained from the first reverse osmosis membrane device is purified by filtering the biologically treated water with the first reverse osmosis membrane device. There is also an advantage that it can be obtained as water.

JP 2008-55317 A JP 2010-149100 A

However, the biologically treated water contains organisms (bacteria, protozoa, metazoans, etc.), residual organic matter that remains without being decomposed by the organism, and secretions secreted by the organism. In the seawater desalination method and seawater desalination apparatus of Patent Document 2, the organism, the residual organic matter, and the secretions are RO membranes of a first reverse osmosis membrane device (hereinafter also referred to as “first RO membrane”). The first RO membrane may be clogged (also referred to as “fouling”, in particular, “fouling” derived from organisms is also referred to as “biofouling”). In addition, the biologically treated water is usually temporarily stored in the biologically treated water storage tank while being transferred from the biologically treated tank to the first reverse osmosis membrane device, and the biologically treated water is stored in the biologically treated water reservoir. In this case, microorganisms are mixed into the biologically treated water through air or the like, and as a result, biofouling may occur due to the microorganisms. In some cases, the organism attached to the RO membrane secretes and proliferates secretions to form biofouling. Biofouling may progress as a result of organisms attached to the first RO membrane secreting secretions and continuing to grow.
Biofouling is a factor that increases the resistance of water (flow path resistance) when passing through the membrane surface of the first RO membrane. Therefore, in a state where biofouling has progressed in the first RO membrane, in order to obtain purified water with the same flux as before biofouling occurs, the pressure for feeding biologically treated water to the first RO membrane is increased. As a result, a great deal of energy (power) is required. Furthermore, when biological treatment water is sent to the first reverse osmosis membrane device in a state where a large flow resistance is generated in the first RO membrane element of the first reverse osmosis membrane device, a load is applied to the first RO membrane element, The first RO membrane of the first RO membrane element may be damaged. In addition, in a state where biofouling has progressed in the first RO membrane, when biologically treated water is supplied to the first reverse osmosis membrane device at the same pressure as before biofouling occurs, the flux of permeate as purified water obtained is obtained. There is a problem that becomes smaller.
In order to solve such a problem, it is conceivable to wash the first RO membrane or suppress biofouling. However, chemicals used for washing (alkali, acid, oxidizing agent, reducing agent, etc.) The cost of biofouling inhibitors (chlorine compounds, etc.) is high, and the first reverse osmosis membrane device is stopped for cleaning or the like, so that a desired amount of purified water cannot be obtained. There is a problem. Moreover, since it becomes impossible to obtain the 1st concentrated water for diluting seawater by stopping the said 1st reverse osmosis membrane apparatus, it is purified water efficiently from seawater using a 2nd reverse osmosis membrane apparatus. There is a problem that the second permeated water cannot be obtained.

  This invention makes it a subject to provide the seawater desalination method and seawater desalination apparatus which can suppress biofouling, obtaining purified water using biologically treated water and seawater in view of the said problem.

In the present invention, biological treated water obtained by biological treatment of organic wastewater is filtered with a first reverse osmosis membrane device to obtain concentrated water, and the concentrated water is diluted with seawater to obtain mixed water. , A seawater desalination method of filtering the mixed water with a second reverse osmosis membrane device,
Biologically treated water is filtered through the first reverse osmosis membrane device to obtain a first concentrated water, the first concentrated water and seawater are mixed to obtain a first mixed water, and the second reverse osmosis membrane device is used to A first step of filtering the first mixed water and a biologically treated water by the second reverse osmosis membrane device to obtain a second concentrated water, and then mixing the second concentrated water and seawater to perform the second mixing In the seawater desalination method, water is obtained, and the second step of filtering the second mixed water with the first reverse osmosis membrane device is alternately performed.

According to such a seawater desalination method, organisms and the like contained in the biologically treated water in the first step can adhere to the first RO membrane of the first reverse osmosis membrane device, but after the first step, the By performing the second step, the second mixed water containing seawater is filtered by the first reverse osmosis membrane device, so that the organism attached to the first RO membrane is caused by salt or the like in the second mixed water. It is difficult to grow, and there is an advantage that biofouling of the first RO membrane can be suppressed.
In addition, according to such a seawater desalination method, not only the first RO membrane but also the reverse osmosis membrane of the second reverse osmosis membrane device (hereinafter also referred to as “second RO membrane”) has the same advantage. There is. That is, in the second step, the organism or the like may adhere to the second RO membrane of the second reverse osmosis membrane device, but the first step that includes seawater is performed by performing the first step after the second step. Since the mixed water is filtered by the second reverse osmosis membrane device, the organism attached to the second RO membrane becomes difficult to grow due to salt or the like in the first mixed water, thereby suppressing biofouling of the second RO membrane. There is an advantage that you can.
Furthermore, according to such seawater desalination method, permeated water as purified water can be obtained by filtering the mixed water containing seawater and the biologically treated water with a reverse osmosis membrane device.
That is, according to the seawater desalination method, biofouling can be suppressed while obtaining purified water using biologically treated water and seawater.

In addition, the present invention includes a first reverse osmosis membrane device that obtains concentrated water by filtering biologically treated water obtained by biologically treating organic wastewater, and the concentrated water is mixed with seawater as dilution water. A seawater desalination apparatus comprising a second reverse osmosis membrane apparatus configured to filter the mixed water.
Biologically treated water is filtered through the first reverse osmosis membrane device to obtain a first concentrated water, the first concentrated water and seawater are mixed to obtain a first mixed water, and the second reverse osmosis membrane device is used to A first step of filtering the first mixed water and a biologically treated water by the second reverse osmosis membrane device to obtain a second concentrated water, and then mixing the second concentrated water and seawater to perform the second mixing The seawater desalination apparatus is configured so that water can be obtained and the second step of filtering the second mixed water with the first reverse osmosis membrane apparatus can be alternately performed.

  As described above, according to the present invention, it is possible to provide a seawater desalination method and a seawater desalination apparatus capable of suppressing biofouling while obtaining purified water using biologically treated water and seawater.

It is the schematic of the seawater desalination apparatus in one Embodiment of this invention. It is a schematic diagram showing one state of the embodiment. It is a schematic diagram showing one state of the embodiment. It is a figure for demonstrating the advantage of the seawater desalination apparatus in embodiment of this invention. It is the schematic of the seawater desalination apparatus in other embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, the seawater desalination apparatus according to this embodiment will be described.

FIG. 1 is a schematic diagram of a seawater desalination apparatus according to the present embodiment.
As shown in FIG. 1, a seawater desalination apparatus 10 according to this embodiment includes a biological treatment tank 11 that biologically treats organic wastewater B to obtain biologically treated water, a microfiltration membrane (MF membrane), and an ultrafiltration membrane. A first turbidizer 12 having at least one of (UF membrane) and turbidizing biologically treated water by filtration to obtain a first turbidized treated water, and a first pressure for pressurizing the first turbidized treated water A pressure unit 13, a first reverse osmosis membrane device 14 for obtaining a first permeated water and a first concentrated water as purified water C by filtering the pressurized first turbidity-treated water as biologically treated water, and microfiltration A second turbidity device 15 having at least one of a membrane (MF membrane) and an ultrafiltration membrane (UF membrane) and turbidizing seawater A by filtration to obtain second turbidized treated water; The second turbidity-treated water and the first concentrated water are mixed to obtain a first mixed water, and a first pressure is applied to the first mixed water. It includes a pressurizing section 17, and a second reverse osmosis unit 18 for filtering processing of the first mixed water pressurized.

The seawater A is water containing salt, for example, water having a salt concentration of 1.0% by mass or more and 8.0% by mass or less. More specifically, the salt concentration is 2.5% by mass or more, for example. It is 6.0 mass% or less.
In this specification, the seawater A is not limited to the water which exists in the sea, If it is water whose salt concentration is 1.0 mass% or more, the water of a lake (salt lake, brackish lake), swamp water, pond water, etc. Including water existing on the land.

The organic waste water B is waste water containing organic matter, for example, waste water having a BOD (biochemical oxygen demand) of 2000 mg / L or less as an indicator of organic matter concentration, and more specifically, 100 to 2000 mg. / L wastewater. The organic waste water B is water having a lower salt concentration than seawater. The organic wastewater B has, for example, a ratio of the salt concentration of the organic wastewater B to the salt concentration of the seawater A of 0.1 or less, more specifically, the salt concentration of the organic wastewater B with respect to the salt concentration of the seawater A. The ratio is 0.01 or less.
Examples of the organic waste water B include sewage (domestic waste water, rain water flowing into the sewer, etc.), industrial waste water (waste water discharged from factories such as food factories, chemical factories, electronics industry factories, and pulp factories). It is done.

  The biological treatment is a treatment for decomposing organic substances contained in water by biological species such as bacteria, protozoa, and metazoans. Examples of the biological treatment include aeration treatment using activated sludge.

  In this specification, turbidity means removing coarse impurities (for example, a solid substance etc.) rather than separating with a reverse osmosis membrane device before filtering with a reverse osmosis membrane device. It means that the filtration is coarser than the membrane filtration or the sedimentation is performed.

  The first turbidity removal device 12 includes a filtration membrane having at least one of an MF membrane and a UF membrane. The filtration membrane is installed as an immersion membrane under the liquid surface of the biological treatment tank 11.

  Examples of the pressurizing units 13 and 17 include a pump.

  The reverse osmosis membrane devices 14 and 18 include an RO membrane and a pressure vessel that accommodates the RO membrane. The RO membrane in this specification is a concept including a nanofiltration membrane (NF membrane).

  The second turbidity removal device 15 includes a filtration membrane having at least one of an MF membrane and a UF membrane, and a pressure vessel that accommodates the filtration membrane.

In addition, as shown in FIG. 2, the seawater desalination apparatus 10 according to the present embodiment biologically treats the organic wastewater B in the biological treatment tank 11 to obtain biologically treated water. To obtain the first turbidized treated water, pressurize the first turbidized treated water with the first pressurizing unit 13, and filter the pressurized first turbidized treated water with the first reverse osmosis membrane device 14. The first permeated water and the first concentrated water as the purified water C are obtained by treatment, and the seawater A is turbidized by the second turbidity removing device 15 to obtain the second turbidized treated water. Concentrated water is mixed by the mixing unit 16 to obtain first mixed water, the first mixed water is pressurized by the second pressurizing unit 17, and the pressurized first mixed water is filtered by the second reverse osmosis membrane device 18. It is comprised so that the 1st process of processing and obtaining the 3rd permeated water and the 3rd concentrated water D which are fresh water can be implemented.
In the seawater desalination apparatus 10 of the present embodiment, the organic waste water B is transferred to the biological treatment tank 11 and the first turbidity-treated water is transferred to the first reverse osmosis membrane apparatus 14 when the first step is performed. The first permeated water is transferred to the purified water storage tank (not shown) as the purified water C, the first concentrated water is transferred to the mixing unit 16, the seawater A is transferred to the second turbidizer 15, 2 The turbidity-treated water is transferred to the mixing unit 16, the first mixed water is transferred to the second reverse osmosis membrane device 18, and the third permeated water as fresh water is used as purified water E in a purified water storage tank (not shown). The third concentrated water D is transferred and is transferred to a concentrated water storage tank (not shown).
Furthermore, the seawater desalination apparatus 10 according to the present embodiment includes a plurality of paths. For example, a first transfer path 20a for transferring the first turbidity-treated water to the first reverse osmosis membrane apparatus 14, and a first concentration. A second transfer path 20b for transferring water to the mixing unit 16, a third transfer path 20c for transferring the first mixed water to the second reverse osmosis membrane device 18, and a third concentrated water D for the concentrated water storage tank (not shown). A fourth transfer path 20d for transferring to the second transfer path 20d.

Furthermore, as shown in FIG. 3, the seawater desalination apparatus 10 according to the present embodiment biologically treats the organic wastewater B in the biological treatment tank 11 to obtain biologically treated water. To obtain the first turbidity-treated water, pressurize the first turbidity-treated water with the first pressurizing unit 13, and filter the pressurized first turbidity-treated water with the second reverse osmosis membrane device 18. The second permeated water and the second concentrated water are obtained by treatment, and the seawater A is turbidized by the second turbidizer 15 to obtain the second turbidized treated water, and the second turbidized treated water and the second concentrated water are obtained. The second mixed water is obtained by mixing in the mixing unit 16, the second mixed water is pressurized by the second pressurizing unit 17, and the pressurized second mixed water is filtered by the first reverse osmosis membrane device 14. Thus, the second step of obtaining the fourth permeated water and the fourth concentrated water F can be performed.
In the seawater desalination apparatus 10 of the present embodiment, the organic waste water B is transferred to the biological treatment tank 11 and the first turbidity-treated water is transferred to the second reverse osmosis membrane apparatus 18 when the second step is performed. The second permeated water is transferred to the purified water storage tank (not shown) as the purified water E, the second concentrated water is transferred to the mixing unit 16, the seawater A is transferred to the second turbidizer 15, 2 The turbidity-treated water is transferred to the mixing unit 16, the second mixed water is transferred to the first reverse osmosis membrane device 14, and the fourth permeated water, which is fresh water, is used as purified water C in a purified water storage tank (not shown). The fourth concentrated water F is transferred and is transferred to a concentrated water storage tank (not shown).
Furthermore, the seawater desalination apparatus 10 of the present embodiment has, for example, a fifth transfer path 20e for transferring the first turbidity-treated water to the second reverse osmosis membrane device 18 and the third concentrated water, in addition to the above-described paths. A sixth transfer path 20f for transferring the second mixed water to the first reverse osmosis membrane device 14, and a fourth concentrated water F for the concentrated water storage tank (not shown). And an eighth transfer path 20h.

  Furthermore, the seawater desalination apparatus 10 of the present embodiment includes a valve interposed in each transfer path. Specifically, the seawater desalination apparatus 10 of the present embodiment uses the first transfer path 20a, the second transfer path 20b, the third transfer path 20c, the fourth transfer path 20d, and the second valve as the valves. A first valve 19a, a second valve 19b, a third valve 19c, and a fourth valve interposed in the fifth transfer path 20e, the sixth transfer path 20f, the seventh transfer path 20g, and the eighth transfer path 20h, respectively. 19d, a fifth valve 19e, a sixth valve 19f, a seventh valve 19g, and an eighth valve 19h.

Moreover, the seawater desalination apparatus 10 of this embodiment is provided with the valve mechanism which determines a flow path by opening / closing operation of each valve. Moreover, the seawater desalination apparatus 10 of this embodiment is the said 1st process because the said 1st-4 valve is made into an open state by the said valve mechanism, and the said 5th-8th valve is made into a closed state. It is configured to be implemented. Furthermore, in the seawater desalination apparatus 10 of the present embodiment, the second step is performed by the valve mechanism in which the first to fourth valves are closed and the fifth to eighth valves are opened. It is configured to be implemented.
Thus, since the seawater desalination apparatus 10 of this embodiment is comprised so that each valve may be opened and closed by the said valve mechanism, it can implement the said 1st process and the said 2nd process alternately. it can.

The salt concentration of the mixed water obtained in the mixing unit 16 preferably exceeds 0.2M (0.2 mol / L) when non-halophilic organisms are contained in the biologically treated water. In addition, when the biologically treated water contains non-halophilic organisms and low-halophilic organisms, the salt concentration is more preferably more than 0.5M. The salt concentration that sufficiently suppresses the growth of non-halophilic organisms is 0.2M, and the salt concentration that sufficiently suppresses the growth of non-halophilic organisms and low-halogenated organisms is 0.5M. is there.
Further, the salt concentration of the mixed water is preferably 0.8M or less, and more preferably 0.6M or less.

  Hereinafter, the reason why the salt concentration of the mixed water is preferably in the above range will be described in detail with reference to FIG.

  As shown in FIG. 4, the lower the volume ratio (seawater mixing ratio) of seawater in water supplied to one reverse osmosis membrane device (hereinafter also referred to as “feedwater”), the lower the salt concentration of the feedwater (feedwater) Salt concentration). For this reason, since the energy which pressurizes supply water is small compared with the case where it consists only of seawater, the amount of energy required in order to desalinate seawater per quantity of the freshwater which is the purified water obtained can be suppressed. Thus, in order to reduce the required energy, it is preferable that the seawater mixing ratio is small.

However, in FIG. 4, when the seawater mixing ratio is 30% or less, that is, when the salt concentration of the feed water is 0.2 M or less, the atmosphere is non-halophilic, and thus non-halophilic organisms grow. Is possible. When the seawater mixing ratio is more than 30% and 80% or less, that is, when the salt concentration of the feed water is more than 0.2M and 0.5M or less, the atmosphere is low in halophilicity. A moderately halophilic organism can grow.
Here, the living thing which exists in supply water is demonstrated. When organisms are classified by salt tolerance, they are divided into highly halophilic organisms, moderately halophilic organisms, lowly halophilic organisms, and non-halophilic organisms. Highly halophilic organisms are organisms with optimal growth NaCl concentrations above 2.5M. The moderately halophilic organisms include bacteria that have an optimal growth NaCl concentration of more than 0.5M and not more than 2.5M, and are separated from various salt-containing samples. The low-degree halophilic organism has an optimal growth NaCl concentration of more than 0.2M and 0.5M or less, and examples include marine higher organisms and bacteria. Non-halophilic organisms have an optimal growth NaCl concentration of more than 0 M and not more than 0.2 M, and many higher organisms and soil bacteria are applicable.

If the salt concentration of seawater is 3.5% by mass, it becomes 0.6M in terms of NaCl (MW: molar mass = 58.44). Moreover, when the salt concentration of biologically treated water is 0.024% by mass, it becomes 0.004M in terms of NaCl, and is concentrated water obtained by filtration using the first turbidity removal device 12 and one reverse osmosis membrane device. The salt concentration is about 0.02M.
As shown in FIG. 4, when the seawater mixing ratio is 0%, that is, when the supply water is only concentrated water derived from biologically treated water (concentrated water 100%), the salt concentration of the supply water is 0.02M. When the seawater mixing ratio is 20%, that is, when the supply water is 20% seawater and 80% concentrated water, the salt concentration of the supply water is 0.12M. When the seawater mixing ratio is 40%, that is, when the supply water is 40% seawater and 60% concentrated water, the salt concentration of the supply water is 0.24M. When the seawater mixing ratio is 60%, that is, when the supply water is 60% seawater and 40% concentrated water, the salt concentration of the supply water is 0.36M. When the seawater mixing ratio is 80%, that is, when the supply water is 80% seawater and 20% concentrated water, the salt concentration of the supply water is 0.50M. When the seawater mixing ratio is 100%, that is, when the supply water is only seawater (seawater 100%), the salt concentration of the supply water is 0.60M.

The growth of the organism is sufficiently suppressed outside the range of the optimal growth NaCl concentration, and particularly when the concentration is higher than the optimal growth NaCl concentration, the growth is effectively suppressed and the organism may be killed. For this reason, as shown in FIG. 4, when the seawater mixing ratio of the feed water is 30% or less, the salt concentration of the feed water is 0.2 M or less, so that non-halophilic organisms can grow. . In addition, when the seawater mixing ratio of the feed water is more than 30% and 80% or less, the salt concentration of the feed water is more than 0.2M and less than 0.5M, so that low-halophilic organisms can grow. is there. However, if the ratio of the seawater is increased so that the salt concentration of the feed water exceeds 0.5M, the growth of non-halophilic organisms and low-degree halophilic organisms is sufficiently suppressed. The biologically treated water contains a relatively large amount of non-halophilic organisms and low-degree halophilic organisms. Therefore, after the biologically treated water is filtered by one reverse osmosis membrane device, the salt concentration is 0 after the non-halophilic organism and the low halophilic organism adhere to the RO membrane of the one reverse osmosis membrane device. By filtering mixed water exceeding 5M with the one reverse osmosis membrane device, it is possible to sufficiently suppress the growth of non-halophilic and low-halophilic organisms attached to the one reverse osmosis membrane device. .
Therefore, when the salt concentration of the mixed water falls within the above preferable range, biofouling can be sufficiently suppressed while reducing the energy required for seawater desalination.

  The seawater desalination method of the present embodiment is a method of alternately performing the first step and the second step using the seawater desalination apparatus of the present embodiment.

  The seawater desalination method and seawater desalination apparatus according to the present embodiment have the above-described configuration, but the seawater desalination method and seawater desalination apparatus according to the present invention are not limited to the above-described configuration, and may be appropriately changed in design. Is possible.

  For example, in the seawater desalination apparatus of the present embodiment, the filtration membrane of the first turbidity removal apparatus 12 is installed as a submerged membrane below the liquid surface of the biological treatment tank 11, but the seawater desalination apparatus of the present invention. Then, the filter membrane of the first turbidity removal device 12 may be of a type installed outside the tank as shown in FIG. In such an embodiment, the first turbidity removal device 12 may include a storage container that stores the filtration membrane.

  Moreover, in the seawater desalination apparatus of this embodiment, although the said 1st turbidity apparatus 12 is equipped with the said filtration membrane, in the seawater desalination apparatus of this invention, the said 1st turbidity removal apparatus 12 is the said filtration. Instead of the membrane, at least one of a sand filtration unit having a sand filter and a precipitation separation tank for separating the water to be treated may be provided. Moreover, in the seawater desalination apparatus of the present invention, the first turbidity removal device 12 may include the filtration membrane, and may further include at least one of the sand filtration means and a precipitation separation tank. Since the sand filter is likely to be clogged with impurities such as solid substances, the first turbidizer 12 further includes a sedimentation separation tank and a biologically treated water in the precipitation separation tank when the sand filtration means is provided. It is preferable that the supernatant is obtained by precipitation separation in step (b), and the supernatant is filtered by the sand filtering means.

  Furthermore, in the seawater desalination apparatus of the present embodiment, the second turbidity removal device 15 includes the filtration membrane. However, in the seawater desalination apparatus of the present invention, the second turbidity reduction device 15 includes the filtration. Instead of the membrane, at least one of a sand filtration unit having a sand filter and a precipitation separation tank for separating the water to be treated may be provided. Moreover, in the seawater desalination apparatus of the present invention, the second turbidity removal device 15 may include the filtration membrane, and may further include at least one of the sand filtration means and the precipitation separation tank. In addition, since the sand filter is easily clogged with impurities such as solid substances, the second turbidizer 15 further includes a sedimentation separation tank when the sand filtration means is provided, and the seawater is precipitated in the precipitation separation tank. It is preferable that the supernatant is obtained by separation and the supernatant is filtered by the sand filtering means.

  DESCRIPTION OF SYMBOLS 10: Seawater desalination apparatus, 11: Biological treatment tank, 12: 1st turbidity removal apparatus, 13: 1st pressurization part, 14: 1st reverse osmosis membrane apparatus, 15: 2nd turbidity reduction apparatus, 16: Mixing part 17: 2nd pressurization part, 18: 2nd reverse osmosis membrane apparatus, A: Seawater, B: Organic waste water, C: Purified water, D: Concentrated water, E: Purified water, F: Concentrated water

Claims (2)

Biologically treated water obtained by biologically treating organic wastewater is filtered through a first reverse osmosis membrane device to obtain concentrated water, and the concentrated water is mixed with seawater as dilution water to obtain mixed water. Is a seawater desalination method in which a second reverse osmosis membrane device is filtered,
Biologically treated water is filtered through the first reverse osmosis membrane device to obtain a first concentrated water, the first concentrated water and seawater are mixed to obtain a first mixed water, and the second reverse osmosis membrane device is used to A first step of filtering the first mixed water and a biologically treated water by the second reverse osmosis membrane device to obtain a second concentrated water, and then mixing the second concentrated water and seawater to perform the second mixing A seawater desalination method characterized by alternately performing a second step of obtaining water and filtering the second mixed water with the first reverse osmosis membrane device. A first reverse osmosis membrane device is provided to filter the biologically treated water obtained by biologically treating organic wastewater to obtain concentrated water, and the concentrated water is mixed with seawater as dilution water to obtain mixed water. And a seawater desalination apparatus provided with a second reverse osmosis membrane device for filtering the mixed water,
Biologically treated water is filtered through the first reverse osmosis membrane device to obtain a first concentrated water, the first concentrated water and seawater are mixed to obtain a first mixed water, and the second reverse osmosis membrane device is used to A first step of filtering the first mixed water and a biologically treated water by the second reverse osmosis membrane device to obtain a second concentrated water, and then mixing the second concentrated water and seawater to perform the second mixing A seawater desalination apparatus configured to alternately perform a second step of obtaining water and filtering the second mixed water with the first reverse osmosis membrane apparatus.

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