JPH0779996B2 - Desalination equipment by reverse osmosis - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desalination apparatus for producing fresh water (produced water) from raw water such as seawater and brackish water using a reverse osmosis membrane.

[0002]

2. Description of the Related Art Generally, a reverse osmosis membrane is often used when producing product water (fresh water) using sea water, brackish water, etc. as raw material water. Since the characteristics of this reverse osmosis membrane change depending on the water temperature, the pressure, and the degree of deterioration of the membrane, it is necessary to appropriately change the usage conditions in accordance with these introductions.

FIGS. 5 (a) to 5 (c) show respective characteristics of the above reverse osmosis membrane. As shown in the figure, as the water temperature and pressure increase, the amount of water produced by the reverse osmosis membrane (that is, the amount of fresh water that permeates the reverse osmosis membrane and is collected) increases, and as the pressure decreases, the salt concentration of the product water increases. Is reduced (that is, the quality of the produced water is deteriorated). In addition, the amount of produced water decreases and the water quality deteriorates as the membrane ages.

By the way, in such a reverse osmosis membrane, when the product water recovery rate (= (produced water amount) / (raw material water amount to be introduced)) exceeds a specified value, the reverse osmosis membrane is clogged and the worst case occurs. In that case, there arises an inconvenience that operation becomes impossible. Therefore, in order to successfully use this reverse osmosis membrane,
It is necessary to keep the production water recovery rate almost constant. For example, when the water temperature rises during use of the reverse osmosis membrane, the recovery rate of the produced water may increase and exceed the specified value, and therefore an operation for lowering the recovery rate is required.
As this operation, it is conceivable to lower the pressure of the raw material water, but as described above, if the pressure is lowered, the salt concentration of the product water increases, so that the satisfactory water quality cannot be obtained. Therefore, conventionally, a method of reducing the number of reverse osmosis membranes used has been used as a means for suppressing the production water recovery rate to a constant value without lowering the pressure.

FIGS. 6A and 6B show an example of a conventional device in which the number of reverse osmosis membranes used is variable. The figure (a) shows the normal operation state, the figure (b) shows the operation state in which the number of reverse osmosis membranes used has been reduced. In each figure, the open valves are open and the black-painted valves are closed. Each valve is shown.

First, in a normal state, as shown in FIG. 6A, the raw material water discharged from the high pressure pump 90 is
The reverse osmosis membrane devices 91a, 91b, 91c are arranged in parallel with each other through the valves 92a, 92b, 92c, respectively, and water, which is a solvent in the raw material water, is permeated through the reverse osmosis membrane in each of the devices 91a to 91c. This water is recovered as product water in the product water outlet through valves 93a, 93b, 93c, respectively, and salt-concentrated water that has not passed through the reverse osmosis membrane in each of the condensers 91a-91c is valves 94a, 94b, 94c.
After passing through the adjusting valve 96, it is collected in the concentrated water outlet.

On the other hand, when the temperature of the raw water rises and the production water recovery rate in each of the reverse osmosis membrane devices 91a to 91c is likely to exceed the specified value, as shown in FIG. , 93c, 94c are fully closed, and the reverse osmosis membrane device used is reduced to two reverse osmosis membrane devices 91a, 91b (that is, the reverse osmosis membrane device 91c is stopped). As a result, the amount of raw material water introduced per reverse osmosis membrane device increases, and along with this, the amount of production water recovered from one reverse osmosis membrane device also increases. The increase amount and the increase amount of the produced water are not in a proportional relationship, and in reality, the produced water does not increase as much as the increase rate of the raw water. That is, by reducing the number of reverse osmosis membrane devices used and increasing the amount of raw water introduced into each reverse osmosis membrane device, one reverse osmosis membrane can be used without lowering the working pressure or increasing the pressure. In this case, the recovery rate of the produced water can be reduced, and thus, the reverse osmosis membrane can be prevented from being blocked without deteriorating the water quality.

[0008]

In the above device, some reverse osmosis membrane devices are suspended when the water temperature rises.
If this reverse osmosis membrane device is left in a rest state, the reverse osmosis membrane will deteriorate due to impurities in the raw water,
The resting reverse osmosis membrane must be preserved with a chemical. With such chemicals,
In particular, for a medium- or large-scale desalination device, it is necessary to attach a chemical treatment facility separately from this device, which causes an increase in facility cost and makes maintenance and management complicated. Further, as an operating method without using such a chemical, a method of shortening the continuous down time of each reverse osmosis membrane device by alternating the reverse osmosis membrane to be stopped at a constant cycle is also used. In addition, the shorter the continuous rest time, the more the number of alternations of the reverse osmosis membrane to be inactivated increases, and there is a disadvantage that the switching operation of valves and the like must be frequently performed for this alternation.

In view of such circumstances, it is an object of the present invention to provide a desalination apparatus capable of maintaining a substantially constant recovery rate of produced water by a simple operation without stopping the reverse osmosis membrane apparatus. To do.

[0010]

The present invention is directed to a desalination apparatus for producing raw water having a solute concentration reduced by passing raw material water containing a solute through a reverse osmosis membrane. A plurality of reverse osmosis membrane devices, a raw material water supply passage for individually supplying raw material water to each reverse osmosis membrane device, a pumping means for pumping raw material water to each reverse osmosis membrane device, and a reverse osmosis membrane device A production water outlet passage for guiding water that has passed through the reverse osmosis membrane to the production water outlet, and a concentrated water outlet passage for guiding water that has not passed through the reverse osmosis membrane in each reverse osmosis membrane device to the concentrated water outlet. In addition, a part of the reverse osmosis membrane device is used as a switching downstream side reverse osmosis membrane device, and at least one reverse osmosis membrane device other than the switching reverse osmosis membrane device is used as a switching upstream side reverse osmosis membrane device. The water that has passed through the reverse osmosis membrane of the upstream side reverse osmosis membrane device is The secondary supply passage for supplying to the side reverse osmosis membrane device, and the water that has been introduced into the raw material water supply passage to all the reverse osmosis membrane devices and the water that has permeated the reverse osmosis membrane passes through the production water outlet passage. The raw water is introduced through the raw water supply passage only to the reverse osmosis membrane device other than the switching downstream side reverse osmosis membrane device and the reverse osmosis membrane of the switching upstream side reverse osmosis membrane device. The permeated water is provided with a supply passage switching means for performing passage switching to a partial series state in which the permeated water is supplied to the switching downstream side reverse osmosis membrane device through the secondary supply passage (claim 1).

Further, a reflux passage for returning water on the front side of the reverse osmosis membrane in the switching downstream side reverse osmosis membrane apparatus to the upstream side of at least one other reverse osmosis membrane apparatus, and the reverse passage in all the reverse osmosis membrane apparatuses. Water that has not permeated the osmosis membrane flows to the concentrated water outlet through the concentrated water outlet passage, and water that has not permeated the reverse osmosis membrane in the switching downstream reverse osmosis membrane device passes through the reflux passage to another. By providing the recirculation passage switching means for switching the passage to the partially recirculated state returned to the upstream side of the reverse osmosis membrane device, the more excellent effect as described later can be obtained (claim 2).

[0012]

In the apparatus according to claim 1, when the water temperature of the raw material water is low, the production water recovery rate in each reverse osmosis membrane apparatus is also low. Raw material water is supplied to the osmosis membrane device, and the water permeated through the reverse osmosis membrane is switched to a state in which it flows through the product water outlet passage to the product water outlet. As a result, as with the conventional apparatus, all reverse osmosis membrane apparatuses can be used equally to produce the product water.

On the other hand, when the water temperature of the raw material water is high, the recovery rate of the produced water in each reverse osmosis membrane device is higher than when the water temperature is low. Partial series condition, that is, the raw material water is supplied only to the reverse osmosis membrane devices other than the specific switching downstream side reverse osmosis membrane device, and the water that has passed through the reverse osmosis membrane of the specific switching upstream side reverse osmosis membrane device is It is switched to a state in which it is supplied to the switching downstream reverse osmosis membrane device through the next supply passage. As a result, the switching downstream side reverse osmosis membrane device is connected in series to the downstream side of the switching upstream side reverse osmosis membrane device, and the number of reverse osmosis membrane devices into which the raw material water is directly introduced is reduced accordingly. Therefore, the production water recovery rate in each reverse osmosis membrane device can be suppressed below a certain level without lowering the pressure and without stopping any of the reverse osmosis membranes.

Moreover, in this partially serial state, the product water that has already passed through the reverse osmosis membrane of the upstream side reverse osmosis membrane apparatus is further passed through the reverse osmosis membrane of the downstream side reverse osmosis membrane apparatus. From the outlet side of the downstream reverse osmosis membrane device, produced water with a further reduced solute concentration is discharged. Therefore, the purity of the finally obtained product water is further improved by the recovery of the product water.

In the apparatus according to the second aspect, when the supply passage switching means switches to the full distribution state, the reflux passage switching means allows the return passage passage means to pass through the entire recovery state, that is, the reverse osmosis membranes in all the reverse osmosis membrane devices. By switching the passage to a state in which the remaining water flows to the concentrated water outlet through the concentrated water outlet passage, the concentrated water generated in each reverse osmosis membrane can be collected in the concentrated water outlet as in the conventional case. . on the other hand,
When a part of the supply passage switching means is switched to the in-series state, the reflux passage switching means causes a part of the reflux state, that is, water that has not passed through the reverse osmosis membrane in the switching downstream side reverse osmosis membrane device to pass through the reflux passage. By switching to a state in which the water is returned to the upstream side of another reverse osmosis membrane device, this water, that is, the water that has once passed through the switching upstream side reverse osmosis membrane device, is the concentrated water derived from the other reverse osmosis membrane device. It can be prevented from being mixed with and recovered, and thus, the reduction of the product water recovery rate in the entire apparatus can be prevented.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS.

The apparatus shown here is provided with a single high-pressure pump (pressure-feeding means) 10, and a plurality (four in the illustrated example) of reverse osmosis membrane devices 12a, 12b, 12 are provided in this high-pressure pump 10.
c and 12d are connected in parallel with each other. More specifically, each of the reverse osmosis membrane devices 12a to 12d has a built-in reverse osmosis membrane for making water, and the front side portions of the reverse osmosis membranes respectively pass through the raw material water supply passages 16a, 16b, 16c, 16d. The high-pressure pump 10 is commonly connected to each of the raw material water supply passages 16a to 16d, and the open / close valves 14a, 1 are provided.
4b, 14c, 14d are provided respectively.

At the downstream side of the reverse osmosis membrane in each of the reverse osmosis membrane devices 12a to 12d, product water outlet passages 18a, 18 are provided.
b, 18c and 18d are respectively connected. Each of the product water outlet passages 18a to 18d is a common product water recovery passage 20.
And is led to a predetermined production water recovery unit (production water derivation unit). Further, on-off valves 22a, 22b, 22c and 22d are provided in the respective product water recovery passages 18a to 18d.

In the reverse osmosis membrane devices 12a to 12d, the concentrated water outlet passage 24 is provided in the non-permeated water discharge portion of the reverse osmosis membrane.
a, 24b, 24c and 24d are respectively connected. The concentrated water discharge passages 24a to 24d join the common concentrated water recovery passage 28 and are guided to a predetermined concentrated water recovery unit (concentrated water discharge unit). In addition, each concentrated water recovery passage 24a-
An opening / closing valve 26a, 26b, 26c, 26d is provided at 24d, and a control valve 30 for pressure adjustment is provided at the concentrated water recovery passageway 28.

Further, as a first feature of this apparatus, the reverse osmosis membrane apparatus 12c is the switching upstream side reverse osmosis membrane apparatus in the present invention, and the reverse osmosis membrane apparatus 12d is the switching downstream side reverse osmosis membrane apparatus in the present invention. , Switching upstream reverse osmosis membrane device 12
In the production water derivation passage 18c connected to c, the switching valve 2
A portion upstream of 2c passes through the secondary supply passage 32,
In the raw material water supply passage 16d connected to the switching downstream reverse osmosis membrane device 12d, the raw water supply passage 16d is connected to a portion downstream of the opening / closing valve 14d. An opening / closing valve 34 is provided in the middle of the secondary supply passage 32, and the opening / closing valve 34 and the opening / closing valves 22c and 14d constitute the supply passage switching means of the present invention.

Further, as a second feature of this apparatus, the front side portion of the reverse osmosis membrane in the switching downstream side reverse osmosis membrane apparatus 12d is connected to the primary side of the high-pressure pump 10 via the return passage 36, and this return passage is connected. A control valve 38 for pressure adjustment is provided in the middle of 36, and by the control valve 38 and the on-off valve 26d provided in the concentrated water outlet passage 24d,
The return passage switching means in the present invention is configured.

Next, the procedure for making water by this apparatus will be described. Similar to FIG. 6, the white valves in FIGS. 1 and 2 are open, and the black valves are closed.

First, when the water temperature of the raw material water is low, the recovery rate of the produced water in each of the reverse osmosis membrane devices 12a to 12d is relatively low, so that the operation of suppressing the recovery rate is not necessary. Therefore,
As shown in FIG. 1, the on-off valve 34 and the control valve 38 are fully closed, and the other valves are opened. By this operation, the raw material water pumped from the high-pressure pump 10 is individually supplied to all the reverse osmosis membrane devices 12a to 12d through the raw material water passages 16a to 16d, and the reverse osmosis membrane devices 12a to 12d are used equally. It will be. Then, the water that has permeated the reverse osmosis membranes of the respective reverse osmosis membrane devices 12a to 12d is produced water discharge passages 18a to 18a.
The concentrated water that has been collected in a predetermined product water recovery section through the d and the product water recovery passage 20 and has not permeated the reverse osmosis membrane in each of the reverse osmosis membrane devices 12a to 12d is the concentrated water outlet passages 24a to 24d and the concentrated water. It is collected in a predetermined concentrated water collecting section through the collecting passage 28.

The recovery rate of the produced water in each of the reverse osmosis membrane devices 12a to 12d can be adjusted by operating the control valve 30. For example, if the operating pressure in each of the reverse osmosis membrane devices 12a to 12d is increased by narrowing the opening / closing valve 30, the recovery rate can be increased accordingly.

On the other hand, when the water temperature of the raw material water is high, the recovery rate of the produced water in each of the reverse osmosis membrane devices 12a to 12d is higher than that when the water temperature is low. Therefore, in order to suppress this, as shown in FIG. On-off valves 22c, 14d, 26d
Is fully closed and other valves are opened. By this operation, the reverse osmosis membrane devices 12a to 12a other than the switching downstream side reverse osmosis membrane device 12d.
Raw material water is introduced directly into the raw material water supply passages 16a to 16c only in 12c. The product water generated by the reverse osmosis membrane devices 12a and 12b is directly supplied to the product water outlet passage 18a,
The water, which is guided to the product water recovery unit through the 18b and the product water recovery passage 20, passes through the reverse osmosis membrane of the switching upstream reverse osmosis membrane device 12c, and the water which has passed through the secondary supply passage 32 is the switching downstream reverse osmosis membrane device 12d. Is supplied to the inlet side of the reverse osmosis membrane device 12d with the impurity concentration further reduced,
It is mixed with other product water through the product water outlet passage 18d.

That is, in the state of FIG. 2, the switching downstream side reverse osmosis membrane device 12d is connected in series via the secondary supply passage 32 to the downstream side of the switching upstream side reverse osmosis membrane device 12c. As a result, the number of reverse osmosis membrane devices to which raw water is directly introduced has been reduced from four to three. Due to this reduction in the number of used water, both the amount of raw water supplied to the reverse osmosis membrane device and the amount of produced water increase, but as the amount of raw water increases, the corresponding increase in the amount of produced water decreases. Therefore, as a result, the recovery rate of the produced water in each reverse osmosis membrane device decreases due to an increase in the amount of raw material water supplied to each reverse osmosis membrane device. Therefore, by switching to the partial series state of FIG. 2, it is possible to suppress the production water recovery rate in each of the reverse osmosis membrane devices 12a to 12d to a certain level or less without lowering the pressure and in some cases increasing the pressure. it can.

Moreover, the high-purity product water purified in two stages by the switching upstream reverse osmosis membrane device 12c and the switching downstream reverse osmosis membrane device 12d is produced by the other reverse osmosis membrane devices 12a, 12b. As a result, the purity of the product water finally obtained is further improved. Further, the water on the front side of the reverse osmosis membrane in the switching downstream side reverse osmosis membrane device 12d, that is, the water that has already been purified by the switching upstream side reverse osmosis membrane device 12c, is the other reverse osmosis membrane devices 12a to 12d. Instead of mixing with the concentrated water derived from
Since it is returned to the upstream side of the high-pressure pump 10 through this, it is possible to prevent the production water recovery efficiency of the entire apparatus from decreasing.

Further, in the conventional device shown in FIG.
During the period when the water temperature of the raw material water is high, it is necessary to perform valve switching work many times in order to replace the reverse osmosis membrane device to be stopped, but in the device shown in this example, there is no reverse osmosis membrane device to be stopped. When the water temperature becomes high, once the state is changed to the state shown in FIG. 2 by switching the valve, it is not necessary to perform the switching until the water temperature falls, so the labor required for the operation becomes extremely small.

In this state of FIG. 2, the recovery rate of the produced water in the reverse osmosis membrane devices 12a to 12c is as shown in FIG.
The adjustment of the control valve 30 can be performed in the same manner as in the above case, and the production water recovery rate in the switching downstream reverse osmosis membrane device 12d can be adjusted by the operation of the control valve 38 in the return passage 36.

Next, a second embodiment will be described with reference to FIGS.

This embodiment will be described in comparison with the first embodiment. Each raw water supply passage 1 in the first embodiment will be described.
High-pressure pumps 10a to 10d are provided at 6a to 16d, respectively, and the reflux passage 36 is made up of the raw material water supply passages 16a to 16d.
It reaches the upstream side of d. Each production water derivation passage 18a-1
The open / close valve in 8c is omitted, and the open / close valves 22 and 40 are provided only in the produced water recovery passage 20 and the produced water outlet passage 18d, respectively. The upstream side of the secondary supply passage 32 is connected to a close position. Further, in the product water outlet passage 18d, a second product water outlet passage 42 is provided between the on-off valve 40 and the switching downstream side reverse osmosis membrane device 12d.
On-off valve 2 in the product water recovery passage 20
2 to the downstream side, and the second production water outlet passage 42
A switching valve 44 is provided midway.

Also in this apparatus, as shown in FIG.
Only the open / close valves 34 and 44 and the control valve 38 are fully closed, and the other valves are opened to operate the high pressure pumps 10a to 10d, thereby distributing the raw material water to all the reverse osmosis membrane devices 12a to 12d, and simultaneously. Processing can be performed. In contrast,
As shown in FIG. 4, the on-off valves 22, 40, 14d, 26d
When the valve is closed and another valve is opened, a part of the product water outlet passage 18d serves as a secondary supply passage, and the three reverse osmosis membranes are provided through the product water outlet passage 18d and the secondary supply passage 32. All the production water derived from the devices 12a to 12c will be supplied to the upstream side of the switching downstream side reverse osmosis membrane device 12d. Then, this switching downstream side reverse osmosis membrane device 12
The product water that has been two-stage purified by d is the second product water outlet passage 4
The water on the front side of the reverse osmosis membrane in the switching downstream side reverse osmosis membrane apparatus 12d (mixed water of the production water that has once passed through the respective reverse osmosis membrane apparatuses 12a to 12c) is guided to the produced water recovery passageway 20 through 2 By being returned to the raw material water supply passages 16a to 16d through the reflux passage 36, it is possible to prevent the production water recovery efficiency of the entire apparatus from being lowered.

That is, in this embodiment, all the reverse osmosis membrane devices 12a to 12c other than the switching downstream side reverse osmosis membrane device 12d are the switching upstream side reverse osmosis membrane devices of the present invention, and the open / close valves 22, 40, Reference numerals 34, 14d and 44 constitute supply passage switching means. As described above, in the present invention, the number of switching upstream-side reverse osmosis membrane devices does not matter, and similarly, the number of switching downstream-side reverse osmosis membrane devices and the total number of reverse osmosis membrane devices do not matter.

Further, in the present invention, as shown in the second embodiment, a high pressure pump 10d or the like is arranged between the switching upstream side reverse osmosis membrane device 12c and the switching downstream side reverse osmosis membrane device 12d, and the power thereof is used. Pressure may be fed from the switching upstream side reverse osmosis membrane device 12c to the switching downstream side reverse osmosis membrane device 12d, or, as shown in the first embodiment, the back pressure of the switching upstream side reverse osmosis membrane device 12c may be reduced. You may make it perform the said pressure feeding. Further, the water that has passed through the return passage 36 does not have to be returned to all the other raw material water supply passages, but may be returned to only some of the raw material water supply passages.

[0035]

As described above, according to the present invention, the total distribution state in which the raw material water is distributed to the respective reverse osmosis membrane devices in parallel, and the specific switching upstream side reverse osmosis membrane device of the above-mentioned reverse osmosis membrane device. Switching to the downstream side It is possible to switch to a partial series state in which the downstream side reverse osmosis membrane devices are connected in series, so the production water recovery rate in each reverse osmosis membrane device exceeds a certain value at high water temperature etc. If there is a risk, the reverse osmosis can be directly supplied with the raw material water without stopping the reverse osmosis membrane device, and without lowering the pressure, by a simple operation of switching the entire device to the above-mentioned part in series. It is possible to reduce the number of membrane devices, which has the effect of preventing clogging of the reverse osmosis membrane due to excessive production water recovery. Further, since the raw water is purified in two stages by the switching upstream reverse osmosis membrane device and the switching downstream reverse osmosis membrane device, by collecting the high-purity produced water obtained by this, the quality of the produced water can be improved. Improvement can be achieved at the same time.

Further, in the apparatus according to claim 2, in the partially in-line state, the water on the front side of the reverse osmosis membrane in the switching downstream side reverse osmosis membrane apparatus is passed through the reflux passage to the upstream side of the other reverse osmosis membrane apparatus. By switching to the partial return state to be returned,
This water, that is, the water that has already passed through the switching upstream reverse osmosis membrane device can be prevented from being collected together with other concentrated water, and thus the reduction of the efficiency of collecting the produced water of the entire device can be prevented. effective.

[Brief description of drawings]

FIG. 1 is a flow sheet showing a state in which a water producing apparatus according to a first embodiment of the present invention is switched to a full distribution state and a full recovery state.

FIG. 2 is a flow sheet showing a state in which the desalination apparatus is partially switched to a serial state and a partial reflux state.

FIG. 3 is a flow sheet showing a state in which the water producing apparatus according to the second embodiment of the present invention is switched to a full distribution state and a full recovery state.

FIG. 4 is a flow sheet showing a state in which the water producing apparatus is switched to a partially in-series state and a partially recirculated state.

5 (a), (b) and (c) are graphs showing respective characteristics of a reverse osmosis membrane.

6 (a) and 6 (b) are flow sheets showing an example of a conventional desalination apparatus.

[Explanation of symbols]

10, 10a, 10b, 10c, 10d High pressure pump (pressure feeding means) 12a, 12b Reverse osmosis membrane device 12c Switching upstream reverse osmosis membrane device 12d Switching downstream side reverse osmosis membrane device 14d, 22, 22c, 34, 40 Open / close valve ( Supply passage switching means) 16a, 16b, 16c, 16d Raw material water supply passages 18a, 18b, 18c, 18d Product water derivation passages 24a, 24b, 24c, 24d Concentrated water derivation passages 26d Open / close valve (reflux passage switching means) 32 Secondary Supply passage 36 Reflux passage 38 Control valve (reflux passage switching means)

Claims (2)

[Claims] 1. A desalination apparatus for producing raw water having a solute concentration reduced by passing raw water containing solute through a reverse osmosis membrane, comprising a plurality of reverse osmosis membrane apparatuses having a reverse osmosis membrane, A raw material water supply passage for individually supplying the raw material water to each reverse osmosis membrane device, a pumping means for feeding the raw material water to each reverse osmosis membrane device, and a water permeating the reverse osmosis membrane of each reverse osmosis membrane device. The reverse osmosis membrane device is provided with a product water outlet passage for guiding the product water outlet, and a concentrated water outlet passage for guiding water that has not permeated the reverse osmosis membrane in each reverse osmosis membrane device to the concentrated water outlet. A part of the above is used as a switching downstream reverse osmosis membrane device,
At least one reverse osmosis membrane device other than this switching reverse osmosis membrane device is used as a switching upstream reverse osmosis membrane device, and water that has passed through the reverse osmosis membrane of this switching upstream side reverse osmosis membrane device is used as the above switching downstream side reverse osmosis membrane device. And a secondary supply passage for supplying the raw material water to the reverse osmosis membrane device through the raw material water supply passage and the water that has passed through the reverse osmosis membrane passes through the product water outlet passage to the product water outlet portion. Flowed through the reverse osmosis membrane of the switching upstream side reverse osmosis membrane device and the raw material water is introduced through the raw material water supply passage only to the reverse osmosis membrane device other than the switching downstream side reverse osmosis membrane device. A desalination apparatus by reverse osmosis, comprising: a supply passage switching means for performing passage switching to a partial series state in which the switching downstream side reverse osmosis membrane device is supplied through the secondary supply passage. 2. The reverse osmosis water production apparatus according to claim 1, wherein the water on the front side of the reverse osmosis membrane in the switching downstream side reverse osmosis membrane apparatus is returned to the upstream side of at least one other reverse osmosis membrane apparatus. And a return passage for all the reverse osmosis membranes and all the recovered state in which the water drawn from the front side of the reverse osmosis membrane flows to the concentrated water outlet through the concentrated water outlet passage and the switching downstream side reverse osmosis membrane. The apparatus is provided with a reflux passage switching means for performing passage switching to a partial reflux state in which water drawn out from the front side of the reverse osmosis membrane in the apparatus is returned to the upstream side of another reverse osmosis membrane apparatus through the reflux passage. A reverse osmosis water-producing device.