JP2020099870A - Water treatment system, and method for operating the same - Google Patents

Abstract

To provide a technique for reducing a cost consumed for cleaning a separation membrane.SOLUTION: A method includes: filtering raw water by an upstream separation membrane module 10; processing permeated water or concentrated water discharged from the upstream separation membrane module 10 by a downstream treatment unit 11 to generate high osmotic pressure liquid having higher osmotic pressure than osmotic pressure of permeated water; creating a forward osmotic phenomenon on a separation membrane of the upstream separation membrane module 10 by introducing high osmotic pressure liquid into a raw water flow channel of the upstream separation membrane module 10, and cleaning the separation membrane of the upstream separation membrane module 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to a water treatment system and a method of operating the same.

Separation membranes such as microfiltration membranes (MF membranes), ultrafiltration membranes (UF membranes), nanofiltration membranes (NF membranes) and reverse osmosis membranes (RO membranes) are used for the production of ultrapure water and desalination of seawater. It is widely used for waste water treatment, oil field injection water production, food and drink production, etc.

Raw water to be treated by the separation membrane is, for example, industrial wastewater. When wastewater is treated with a separation membrane, dyes, organic substances, chemical oxygen demand (COD) components, etc. are adsorbed and deposited on the surface of the separation membrane to reduce water permeability. Therefore, it is necessary to regularly wash the separation membrane.

Patent Document 1 discloses that RO filtered water containing alkali is circulated in a UF membrane module and then held in that state, and that an acid aqueous solution is circulated in the RO membrane module and then held in that state. Have been described.

JP, 2016-97357, A

The more the cleaning agent such as alkali, acid and special chemical is used, the more the cost for cleaning the separation membrane increases. There is a need to reduce the expense spent cleaning separation membranes.

The present invention provides a technique for reducing the cost of cleaning separation membranes.

The present invention is
Filtering raw water with an upstream separation membrane module,
Generating a hyperosmotic liquid having an osmotic pressure higher than the osmotic pressure of the permeate by treating the permeate or the concentrated water discharged from the upstream separation membrane module with a downstream treatment device;
By introducing the high osmotic pressure liquid into the raw water flow path of the upstream separation membrane module to cause a forward osmosis phenomenon in the separation membrane of the upstream separation membrane module, the separation membrane of the upstream separation membrane module is removed. To wash,
There is provided a method for operating a water treatment system, including:

In another aspect, the invention comprises
An upstream separation membrane module,
A downstream treatment device for producing a hyperosmotic liquid having an osmotic pressure higher than the osmotic pressure of the permeate by treating permeate or concentrated water discharged from the upstream separation membrane module;
A cleaning flow channel that guides the high osmotic pressure liquid from the downstream treatment device to the raw water flow channel of the upstream separation membrane module,
Equipped with
By introducing the high osmotic pressure liquid into the raw water flow path of the upstream separation membrane module to cause a forward osmosis phenomenon in the separation membrane of the upstream separation membrane module, the separation membrane of the upstream separation membrane module is removed. Provide a water treatment system for cleaning.

According to the technique of the present invention, the separation membrane is washed by the normal osmosis phenomenon using the high osmotic pressure liquid generated in the water treatment system. Therefore, the cost of cleaning the separation membrane can be reduced.

FIG. 1 is a configuration diagram of a water treatment system according to the first embodiment of the present invention. FIG. 2A is a configuration diagram of an RO membrane module. FIG. 2B is a configuration diagram showing another connection structure of each flow path. FIG. 3 is an exploded perspective view of an RO membrane element used in the RO membrane module. FIG. 4 is a flowchart of the cleaning operation. FIG. 5: is a block diagram of the water treatment system which concerns on Embodiment 2 of this invention. FIG. 6 is a configuration diagram of a water treatment system according to the third embodiment of the present invention. FIG. 7: is a block diagram of the water treatment system which concerns on Embodiment 4 of this invention. FIG. 8: is a block diagram of the water treatment system which concerns on Embodiment 5 of this invention. FIG. 9: is a block diagram of the water treatment system which concerns on Embodiment 6 of this invention. FIG. 10: is a block diagram of the water treatment system which concerns on Embodiment 7 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments below.

(Embodiment 1)
FIG. 1 shows the configuration of a water treatment system 100 according to the first embodiment. The water treatment system 100 includes an RO membrane module 10, an NF membrane module 11, and a flow path 20. The RO membrane module 10 and the NF membrane module 11 are connected in series in this order. The flow path 20 connects the concentrated water outlet of the RO membrane module 10 and the raw water inlet of the NF membrane module 11. Raw water is supplied to the RO membrane module 10 and filtered in the RO membrane module 10. The concentrated water discharged from the RO membrane module 10 is filtered in the NF membrane module 11. Concentrated water and permeated water are generated in the RO membrane module 10 and the NF membrane module 11, respectively.

The water treatment system 100 may be a ZLD system (zero liquid discharge system). Raw water to be treated by the water treatment system 100 is, for example, industrial wastewater such as wastewater from a dyeing plant. The water treatment system 100 may include other treatment devices such as a UF (ultrafiltration) membrane module, an MF (microfiltration) membrane module, a hardness removing device, an electrodialysis device, and an evaporator, if necessary.

The RO membrane module 10 is an example of an upstream separation membrane module. The RO membrane module 10 includes an RO membrane as a separation membrane. The NF membrane module 11 is an example of a downstream separation membrane module. The NF membrane module 11 includes an NF membrane as a separation membrane, and filters the concentrated water discharged from the RO membrane module 10.

In this specification, the phrase "upstream" is used to mean "disposed upstream". The term "downstream" is used to mean "disposed downstream."

In this specification, the separation membrane module is an example of a processing device. As will be described later, an electrodialysis device is another example of the processing device.

The water treatment system 100 further includes a flow path 21 and a tank 30. The tank 30 is connected to the permeate outlet of the RO membrane module 10 by the flow path 21. Permeate discharged from the RO membrane module 10 is stored in the tank 30.

The water treatment system 100 further includes a flow path 22 and a tank 31. The tank 31 is connected to the permeate outlet of the NF membrane module 11 by the flow path 22. The permeated water discharged from the NF membrane module 11 is stored in the tank 31.

The water treatment system 100 further includes a cleaning flow path 23. The cleaning flow path 23 is a flow path that guides a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the RO membrane module 10 from the NF membrane module 11 to the raw water flow passage of the RO membrane module 10. When performing a cleaning operation in the water treatment system 100, a high osmotic pressure liquid is introduced into the raw water flow path of the RO membrane module 10 to cause a normal osmosis phenomenon in the RO membrane of the RO membrane module 10. As a result, the RO membrane of the RO membrane module 10 is cleaned.

The high osmotic pressure liquid may be a liquid having a total dissolved solids concentration higher than the total dissolved solids (TDS) concentration of the raw water to be introduced into the RO membrane module 10. By using such a liquid as the high osmotic pressure liquid, the forward osmosis phenomenon can be surely caused, and by extension, the fouling substance deposited on the surface of the separation membrane such as the RO membrane can be efficiently removed.

The osmotic pressure can be specified by directly measuring it with an osmometer (for example, 3250 Single-Sample Osmometer manufactured by Advanced Instruments) or estimating it from the measurement result of electric conductivity.

Further, the high osmotic pressure liquid may be a liquid having a COD component concentration lower than the concentration of the COD component in the raw water to be introduced into the RO membrane module 10 which is the upstream separation membrane module. In this embodiment, the hyperosmotic liquid is water that has been filtered at least once with an RO membrane (or NF membrane), and is clean water from which COD components have been removed. A high cleaning effect can be obtained by using such a liquid as the high osmotic pressure liquid. This also applies to other embodiments.

The concentration of the COD component can be measured, for example, using potassium permanganate (KMnO ₄ ) according to a factory drainage test method (JIS K 0102 (2016)).

The flow direction of the hyperosmotic liquid in the washing operation is opposite to the flow direction of the raw water in the normal operation for filtering the raw water. In this case, the dirt attached to the raw water spacer for forming the raw water flow path can be removed at the same time. However, it is also possible to match the flow direction of the high osmotic pressure liquid in the washing operation with the flow direction of the raw water in the normal operation for filtering the raw water.

In this embodiment, the high osmotic pressure liquid contains the permeated water discharged from the NF membrane module 11. That is, the high osmotic pressure liquid used for cleaning the RO membrane module 10 is self-supplied by the water treatment system 100. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. The high osmotic pressure liquid may contain only the permeated water discharged from the NF membrane module 11. The high osmotic pressure liquid may contain other liquids, other additives, etc., as long as it does not cause a great disadvantage that economic efficiency is significantly deteriorated. The hyperosmotic liquid may include, for example, a cleaning agent for cleaning the separation membrane. Further, salts such as NaCl and Na ₂ SO ₄ generated in the water treatment system 100 may be added to increase the osmotic pressure of the high osmotic pressure liquid.

The TDS concentration (total dissolved solids concentration) in the liquid can be measured using, for example, a commercially available TDS meter.

In the present embodiment, the cleaning flow path 23 connects the tank 31 and the high TDS liquid inlet of the RO membrane module 10. The cleaning flow path 23 may be a flow path branched from the flow path 22 or may be a flow path directly connected to the tank 31.

Each of the flow paths 20, 21, 22, and 23 is composed of at least one pipe. Devices such as a pump, a valve, and a sensor may be provided in each flow path, if necessary. These descriptions also apply to the other flow paths described below.

FIG. 2A schematically shows the configuration of the RO membrane module 10. The RO membrane module 10 is composed of a container 59 and at least one RO membrane element 60. At least one RO membrane element 60 is arranged inside the container 59. In the present embodiment, the RO membrane module 10 has a plurality of RO membrane elements 60. The plurality of RO membrane elements 60 are arranged in series so that the raw water sequentially flows through the plurality of RO membrane elements 60. The number of RO membrane elements 60 is not particularly limited and is, for example, 1 to 7. The RO membrane element 60 may be a spiral wound type membrane element.

In the present embodiment, the “raw water channel of the RO membrane module 10” means the raw water channel of the RO membrane element 60 that constitutes the RO membrane module 10. The “permeate flow channel of the RO membrane module 10” means the permeate flow channel of the RO membrane element 60 that constitutes the RO membrane module 10. This also applies to other separation membrane modules, including the NF membrane module 11.

The container 59 has a cylindrical shape. A raw water inlet 71 and a high osmotic pressure liquid outlet 74 are provided at one end of the container 59. At the other end of the container 59, a concentrated water outlet 72, a high osmotic pressure liquid inlet 73 and a permeated water outlet 75 are provided. The raw water inlet 71, the concentrated water outlet 72, the high osmotic pressure liquid inlet 73, and the high osmotic pressure liquid outlet 74 communicate with the raw water flow path of the RO membrane element 60 via the internal space of the container 59. The permeated water outlet 75 communicates with the water collection pipe 61 of the RO membrane element 60. The flow path 20 is connected to the concentrated water outlet 72. The cleaning flow path 23 is connected to the high osmotic pressure liquid inlet 73. The flow path 21 is connected to the permeated water outlet 75.

FIG. 2B shows another connection structure of each flow path. As shown in FIG. 2B, the raw water inlet 71 can also be used as the high osmotic pressure liquid outlet 74 by a connection structure using valves 77 and 78. The concentrated water outlet 72 can also be used as the high osmotic pressure liquid inlet 73. For example, the cleaning flow path 23 is connected to the flow path 20 via the valve 78. Such a structure does not require modification of the structure of existing separation membrane modules. The valves 77 and 78 are, for example, three-way valves. It is also possible to replace the three-way valve with a plurality of on-off valves.

FIG. 3 shows the RO membrane element 60 partially expanded. The RO membrane element 60 is composed of an RO membrane 62, a raw water spacer 63, and a permeate spacer 64. Specifically, the RO membrane element 60 is composed of a plurality of RO membranes 62, a plurality of raw water spacers 63, and a plurality of permeated water spacers 64.

The plurality of RO membranes 62 are superposed on each other, sealed on three sides so as to have a bag-like structure, and wound around the water collection pipe 61. A raw water spacer 63 is disposed between the RO membranes 62 so as to be located outside the bag-shaped structure. The raw water spacer 63 secures a space as a raw water flow path between the RO membranes 62. A permeate spacer 64 is arranged between the RO membranes 62 so as to be located inside the bag-shaped structure. The permeated water spacer 64 secures a space as a permeated water flow path between the RO membranes 62 and 62. The open end of the bag-shaped structure is connected to the water collection pipe 61 so that the permeate flow path communicates with the water collection pipe 61.

The water collection pipe 61 plays a role of collecting the permeated water that has permeated each RO membrane 62 and guiding it to the outside of the RO membrane element 60. The water collection pipe 61 is provided with a plurality of through holes 61h at predetermined intervals along the longitudinal direction thereof. The permeated water flows into the water collecting pipe 61 through these through holes 61h.

Raw water flows through the raw water flow path in parallel with the longitudinal direction of the water collection pipe 61. When cleaning the RO membrane element 60, the hyperosmotic liquid flows through the raw water flow passage in a direction opposite to the flow direction of the raw water.

The NF membrane module 11 may also have the same structure as the RO membrane module 10. “RO” in the description of the RO membrane module 10 can be read as “NF”. However, in this embodiment, the NF membrane module 11 is not provided with a high osmotic pressure liquid inlet and a high osmotic pressure liquid outlet. Alternatively, even if the NF membrane module 11 is provided with a hyperosmotic liquid inlet and a hyperosmotic liquid outlet, they are closed.

The NF membrane used in the NF membrane module 11 may be an NF membrane capable of selectively separating monovalent ions and divalent ions. Specifically, the NF membrane used in the NF membrane module 11 blocks divalent ions and transmits monovalent ions. When the monovalent ions and the divalent ions are sufficiently separated from each other, valuable ions, for example, sulfate ions are easily collected. The NF membrane used in the NF membrane module 11 has excellent divalent ion selective separation performance.

In the present specification, the divalent ion selective separation performance is the performance evaluated by the difference between the blocking rate of monovalent ions and the blocking rate of divalent ions in addition to the blocking rate of divalent ions. When the blocking rate of divalent ions is high and the blocking rate of monovalent ions is low, it can be said that the selective separation performance of divalent ions is excellent. When the difference between the blocking rate of monovalent ions and the blocking rate of divalent ions is small, even if the blocking rate of divalent ions is high, it cannot be said that the selective separation performance of divalent ions is excellent.

The blocking rate of monovalent ions and the blocking rate of divalent ions can be measured by the following methods, for example, according to JIS K 3805 (1990). To measure the inhibition rate of divalent ions, an aqueous MgSO ₄ solution having a concentration of 2000 mg/liter and 25° C., pH 6.5 to 7, is used. To measure the inhibition rate of monovalent ions, an aqueous NaCl solution having a concentration of 2000 mg/liter and 25° C., pH 6.5 to 7, is used.

An MgSO ₄ aqueous solution or an NaCl aqueous solution is permeated through a separation membrane of a predetermined size at an operating pressure of 1.5 MPa. After the preparation step for 30 minutes, the conductivity of the permeated liquid and the supply liquid was measured using a conductivity measuring device, and from the results and the calibration curve (concentration-conductivity), based on the following formula, divalent ions It is possible to calculate the MgSO ₄ blocking rate as the blocking rate and the NaCl blocking rate as the blocking rate of monovalent ions. Instead of measuring the electric conductivity, the concentration may be measured by an ion chromatography method.
· MgSO ₄ rejection (%) = (1- (MgSO 4 concentration of MgSO ₄ concentration / feed permeate)
) X 100
-NaCl inhibition rate (%) = (1-(NaCl concentration of permeate/NaCl concentration of supply liquid)) x 100

For example, when the difference between the blocking rate of monovalent ions and the blocking rate of divalent ions is 15% or more, it can be said that the separation membrane can selectively separate monovalent ions and divalent ions. The difference between the blocking rate of monovalent ions and the blocking rate of divalent ions may be 50% or more. The upper limit of the difference between the blocking rate of monovalent ions and the blocking rate of divalent ions is not particularly limited and is theoretically 100%. The difference between the blocking rate of monovalent ions and the blocking rate of divalent ions can be used as an index of the selective separation performance of divalent ions.

In the present specification, the “NF membrane” means a separation membrane having an NaCl rejection of 5% or more and less than 93% when an aqueous NaCl solution having a concentration of 2000 mg/liter is filtered under the conditions of an operating pressure of 1.5 MPa and 25° C. Means The RO membrane means a separation membrane having a NaCl blocking rate of 93% or more when an aqueous NaCl solution having a concentration of 2000 mg/liter is filtered under the operating pressure of 1.5 MPa and 25° C.

The structure of the separation membrane element used for the RO membrane module 10 and the NF membrane module 11 is not limited to the spiral type, but may be other types such as a hollow fiber type, a tubular type, a frame and plate type (flat plate laminated type). May be. The structure of the RO membrane module 10 may be different from the structure of the NF membrane module 11. This also applies to other separation membrane elements described later.

Next, the operation of the water treatment system 100 will be described.

[Normal operation]
Normal operation is an operation for purifying raw water such as industrial wastewater. During normal operation, raw water is supplied to the raw water inlet of the RO membrane module 10. Raw water is filtered by the RO membrane module 10. Along with this, concentrated water and permeated water are generated in the RO membrane module 10. The permeated water is guided to the tank 30 through the flow path 21, and is temporarily stored in the tank 30. The permeated water is clean water containing almost no solute and is reused as, for example, industrial water. The concentrated water is guided to the NF membrane module 11 through the flow path 20.

The NF membrane module 11 further filters the concentrated water discharged from the RO membrane module 10. Along with this, concentrated water and permeated water are generated in the NF membrane module 11. The concentrated water is processed by, for example, an evaporator. The residue contains, for example, a salt of a divalent ion such as sulfate ion.

The permeated water discharged from the NF membrane module 11 is guided to the tank 31 through the flow path 22 and temporarily stored in the tank 31. The permeated water discharged from the NF membrane module 11 may be a hyperosmotic liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the RO membrane module 10. The salt concentration of the permeated water discharged from the NF membrane module 11 may be higher than the salt concentration of the raw water to be introduced into the RO membrane module 10. In the NF membrane module 11, a hyperosmotic liquid is generated. A part of the permeated water discharged from the NF membrane module 11 is stored in the tank 31 as a high osmotic pressure liquid and used for cleaning the RO membrane module 10. The rest of the permeated water discharged from the NF membrane module 11 is further processed by a processing device such as an electrodialysis device and an evaporator.

The permeated water discharged from the NF membrane module 11 is, for example, clean water that contains a high concentration of monovalent ions but is free from dyes, organic substances and COD components. Therefore, the permeated water discharged from the NF membrane module 11 can be suitably used as the high osmotic pressure liquid for the cleaning operation.

The TDS concentration of the permeated water discharged from the RO membrane module 10 is, for example, 0.05% to 0.1%. The TDS concentration of the concentrated water discharged from the RO membrane module 10 is 5.5% to 10%, for example. The TDS concentration of the permeated water discharged from the NF membrane module 11 is, for example, 1% to 2.0%.

[Cleaning operation]
The cleaning operation is an operation for removing the fouling substances deposited on the RO film of the RO film module 10. In the present embodiment, the fouling substance is lifted from the RO film and removed by utilizing the forward osmosis phenomenon. In normal operation, water molecules permeate the RO membrane from the raw water channel to the permeate channel. On the other hand, in the washing operation, water molecules permeate the RO membrane from the permeated water channel to the raw water channel.

FIG. 4 is a flowchart of the cleaning operation. In step S1, the supply of raw water to the RO membrane module 10 is stopped, and the high osmotic pressure liquid is introduced into the raw water passage of the RO membrane module 10 through the washing passage 23. The high osmotic pressure liquid is introduced into the container 59 of the RO membrane module 10 and flows into the raw water flow path of each RO membrane element 60.

Immediately after the start of the cleaning operation, the permeate flow path of the RO membrane module 10 is filled with the permeate. Therefore, the forward osmosis phenomenon occurs based on the difference between the osmotic pressure of the high osmotic pressure liquid and the osmotic pressure of the permeated water, and water moves from the permeated water channel to the raw water channel. As a result, the fouling substance deposited on the RO film floats.

In this embodiment, after introducing the high osmotic pressure liquid into the raw water flow path of the RO membrane module 10, the high osmotic pressure liquid is made to stand still in the raw water flow path for a predetermined time in step S2. By resting the hyperosmotic liquid, the hyperosmotic liquid can be saved. Further, when the high osmotic pressure liquid is made to stand still in the raw water flow channel, it is possible to avoid reduction of the osmotic pressure difference due to continuous flow of the high osmotic pressure liquid. Furthermore, the static osmotic pressure liquid may be stopped and the high osmotic pressure liquid may be flown. In other words, the high osmotic pressure liquid may be intermittently caused to flow little by little. By doing so, it is possible to prevent the normal osmosis effect from gradually decreasing due to water permeated by the normal osmosis, and the normal osmosis effect is continuously obtained.

The operation of step S3 is executed in parallel with the operation of step S2. In step S3, the normal osmosis phenomenon is continued by supplying the wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid to the permeate flow passage of the RO membrane module 10. In the present embodiment, permeated water discharged from the RO membrane module 10 as wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid is supplied from the tank 30 to the permeated water channel of the RO membrane module 10. The permeated water is supplied to the permeated water channel based on, for example, the height difference between the tank 30 and the RO membrane module 10. By doing so, damage to the RO membrane module 10 can be prevented. When the RO membrane module 10 is a laminated separation membrane module, it is easy to supply permeate as wash water to the permeate flow channel.

As described with reference to FIGS. 2A and 3, when the RO membrane element 60 of the spiral type is used in the RO membrane module 10, at the start of the cleaning operation, in other words, when the supply of raw water is stopped. The permeate flow path including the internal space of the water collection pipe 61 is filled with permeate. As the forward osmosis phenomenon progresses, the permeated water gradually moves to the raw water channel. According to this embodiment, since the permeated water as the wash water is continuously supplied to the permeated water channel, it is possible to prevent the permeated water from being depleted and the forward osmosis phenomenon to be stopped. Further, according to this embodiment, it is possible to prevent the permeated water from being depleted and the water from being lost from the pores of the separation membrane. As a result, it is possible to prevent the separation membrane from becoming hydrophobic and, in turn, to prevent deterioration of the performance of the separation membrane.

In the present embodiment, the cleaning water includes the permeated water discharged from the RO membrane module 10. That is, the cleaning water used for cleaning the RO membrane module 10 is self-supplied by the water treatment system 100. It is economical because it is not necessary to supply the wash water from outside the water treatment system 100. However, the wash water may be supplied from outside the water treatment system 100. Normal water such as RO water can be used as wash water.

The pressure of the high osmotic pressure liquid in the raw water channel may be a pressure close to atmospheric pressure. As a result, the forward osmosis phenomenon can be efficiently advanced. The pressure of the permeated water in the permeated water channel is, for example, a pressure based on the height difference between the tank 30 and the RO membrane module 10.

Next, in step S4, it is determined whether or not a predetermined time has elapsed from the start of the cleaning operation. When the forward osmosis phenomenon progresses, the osmotic pressure concentration gradually decreases in the vicinity of the surface of the separation membrane in the raw water channel, and the osmotic pressure difference decreases. As a result, the forward osmosis phenomenon stops. By adopting a time period in which the forward osmosis phenomenon is predicted to stop, for example, 5 to 10 minutes as the predetermined time period, the cleaning operation can be completed in a short time period.

After allowing the high osmotic pressure liquid to stand still in the raw water flow path for a predetermined time, in step S5, the supply of the high osmotic pressure liquid to the raw water flow path is restarted and the high osmotic pressure liquid is discharged from the raw water flow path. The high osmotic pressure liquid contains a fouling substance separated from the RO membrane by the forward osmosis phenomenon. A high cleaning effect can be expected by removing the fouling substance by flushing.

The high osmotic pressure liquid discharged from the RO membrane module 10 is returned to, for example, the flow path of raw water or the tank of raw water. That is, the high osmotic pressure liquid used for cleaning the RO membrane of the RO membrane module 10 may be mixed with the raw water and retreated in the water treatment system 100, or may be treated in another treatment device such as an evaporator. Good. When the high osmotic pressure liquid is mixed with the raw water and reprocessed by the water treatment system 100, it is economical because no special treatment device is required. When the high osmotic pressure liquid does not contain a special chemical, the separation membrane such as the RO membrane and the NF membrane is not likely to be damaged.

According to the method of the present embodiment, the upstream separation membrane module (RO membrane module 10) is washed using the high osmotic pressure liquid generated in the downstream treatment device (NF membrane module 11). The hyperosmotic liquid is self-contained by the water treatment system 100. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. Since it is not necessary to use a cleaning agent such as an alkali, an acid or a special chemical, it is possible to reduce the cost spent for cleaning the separation membrane.

Cleaning by the method of the present embodiment can be performed regularly. Since the cleaning by the method of the present embodiment is completed in a short time, the system down time of the water treatment system 100 can be shortened.

The cleaning according to the method of the present embodiment and the conventional cleaning using a cleaning agent may be performed in combination. In this case, the frequency of cleaning with the cleaning agent can be reduced. For example, after the cleaning according to the flowchart of FIG. 4 is performed plural times, the cleaning with the cleaning agent may be performed once. By repeating such a cleaning cycle, not only a high cleaning effect can be obtained, but also cost reduction and system down time can be achieved.

According to the method of the present embodiment, the frequency of contact of the separation membrane with a cleaning agent such as an acid, an alkali or a special chemical can be reduced, so that the life of the separation membrane is extended.

Hereinafter, some other embodiments will be described. Elements common to the first embodiment and other embodiments are given the same reference numerals, and the description thereof may be omitted. The description regarding each embodiment can be applied to each other as long as there is no technical conflict. The respective embodiments may be combined with each other as long as there is no technical conflict.

(Embodiment 2)
FIG. 5 shows the configuration of the water treatment system 200 according to the second embodiment. The water treatment system 200 includes an NF membrane module 11, an RO membrane module 12, and a flow path 24. The NF membrane module 11 and the RO membrane module 12 are connected in series in this order. The flow path 24 connects the permeated water outlet of the NF membrane module 11 and the raw water inlet of the RO membrane module 12. Raw water is supplied to the NF membrane module 11 and filtered in the NF membrane module 11. The permeated water discharged from the NF membrane module 11 is filtered in the RO membrane module 12.

The NF membrane module 11 is an example of an upstream separation membrane module. The RO membrane module 12 is an example of a downstream separation membrane module. The RO membrane module 12 filters the permeated water discharged from the NF membrane module 11.

The water treatment system 200 further includes a flow path 25 and a tank 32. The tank 32 is connected to the permeate outlet of the NF membrane module 11 by the flow path 25. In this embodiment, the flow path 25 is branched from the flow path 24. The permeated water discharged from the NF membrane module 11 is stored in the tank 32.

The water treatment system 200 further includes a flow path 26 and a tank 33. The tank 33 is connected to the concentrated water outlet of the RO membrane module 12 by the flow path 26. The concentrated water discharged from the RO membrane module 12 is stored in the tank 33.

The water treatment system 200 further includes a cleaning channel 27. The cleaning flow channel 27 is a flow channel that guides a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the NF membrane module 11 from the RO membrane module 12 to the raw water flow channel of the NF membrane module 11. When performing a cleaning operation in the water treatment system 200, a high osmotic pressure liquid is introduced into the raw water flow path of the NF membrane module 11 to cause a normal osmosis phenomenon in the NF membrane of the NF membrane module 11. As a result, the NF film of the NF film module 11 is washed.

In this embodiment, the hyperosmotic liquid contains concentrated water discharged from the RO membrane module 12. That is, the high osmotic pressure liquid used for cleaning the NF membrane module 11 is self-supplied by the water treatment system 200. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. The hyperosmotic liquid may contain only the concentrated water discharged from the RO membrane module 12. The high osmotic pressure liquid may contain other liquids, other additives, and the like, as long as they do not bring about a great disadvantage that economic efficiency is significantly deteriorated. The hyperosmotic liquid may include, for example, a cleaning agent for cleaning the separation membrane. Further, salts such as NaCl and Na ₂ SO ₄ generated in the water treatment system 200 may be added to increase the osmotic pressure of the high osmotic pressure liquid. The hyperosmotic liquid may have a TDS concentration higher than that of the raw water to be introduced into the NF membrane module 11.

In the present embodiment, the cleaning flow path 27 connects the tank 33 and the high osmotic pressure liquid inlet of the NF membrane module 11. The cleaning flow path 27 may be a flow path branched from the flow path 26 or may be a flow path directly connected to the tank 33.

The NF membrane module 11 may have the same structure as the RO membrane module 10 of the first embodiment. In this embodiment, the NF membrane module 11 is provided with a high osmotic pressure liquid inlet and a high osmotic pressure liquid outlet.

The RO membrane module 12 may have the same structure as the RO membrane module 10 in the first embodiment. All the description regarding the RO membrane module 10 can be applied to the RO membrane module 12. However, the RO membrane module 12 is not provided with a high osmotic pressure liquid inlet and a high osmotic pressure liquid outlet.

Next, the operation of the water treatment system 200 will be described.

[Normal operation]
During normal operation, raw water is supplied to the raw water inlet of the NF membrane module 11. Raw water is filtered by the NF membrane module 11. Along with this, concentrated water and permeated water are generated in the NF membrane module 11. The concentrated water is processed by, for example, an evaporator. The residue contains, for example, a salt of a divalent ion such as sulfate ion. The permeated water is guided to the RO membrane module 12 through the flow path 24. A part of the permeated water is guided to the tank 32 through the flow path 25 and temporarily stored in the tank 32.

The RO membrane module 12 further filters the permeated water discharged from the NF membrane module 11. Along with this, concentrated water and permeated water are generated in the RO membrane module 12.

The concentrated water discharged from the RO membrane module 12 is guided to the tank 33 through the flow path 26 and temporarily stored in the tank 33. The concentrated water discharged from the RO membrane module 12 may be a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the NF membrane module 11. The salt concentration of the concentrated water discharged from the RO membrane module 12 may be higher than the salt concentration of the raw water to be introduced into the NF membrane module 11. A high osmotic pressure liquid is generated in the RO membrane module 12. A part of the concentrated water discharged from the RO membrane module 12 is stored in the tank 33 as a high osmotic pressure liquid and used for cleaning the NF membrane module 11. The rest of the concentrated water discharged from the RO membrane module 12 is further processed by a processing device such as an electrodialysis device and an evaporator.

The concentrated water discharged from the RO membrane module 12 is, for example, clean water that contains a high concentration of monovalent ions but is free of dyes, organic substances and COD components. Therefore, the concentrated water discharged from the RO membrane module 12 can be suitably used as the high osmotic pressure liquid for the cleaning operation.

The TDS concentration of the permeated water discharged from the NF membrane module 11 is, for example, 1% to 2%. The TDS concentration of the concentrated water discharged from the RO membrane module 12 is, for example, 2% to 3%. The TDS concentration of the permeated water discharged from the RO membrane module 12 is, for example, 0.02% to 0.05%.

[Cleaning operation]
The cleaning operation is an operation for removing the fouling substances deposited on the NF film of the NF film module 11. In this embodiment, the fouling substance is lifted from the NF film by utilizing the forward osmosis phenomenon. In normal operation, water molecules permeate the NF membrane from the raw water channel to the permeate channel. On the other hand, in the washing operation, water molecules permeate the NF membrane from the permeated water channel to the raw water channel.

As described in the first embodiment, the cleaning operation is performed according to the flowchart shown in FIG. In step S1, the supply of raw water to the NF membrane module 11 is stopped, and the high osmotic pressure liquid is introduced into the raw water flow passage of the NF membrane module 11 through the cleaning flow passage 27.

Immediately after the start of the cleaning operation, the permeated water channel of the NF membrane module 11 is filled with permeated water. Therefore, the forward osmosis phenomenon occurs based on the difference between the osmotic pressure of the high osmotic pressure liquid and the osmotic pressure of the permeated water, and water moves from the permeated water channel to the raw water channel. As a result, the fouling substance deposited on the NF film floats.

After introducing the high osmotic pressure liquid into the raw water flow path of the NF membrane module 11, the high osmotic pressure liquid is made to stand still in the raw water flow path for a predetermined time in step S2.

The operation of step S3 is executed in parallel with the operation of step S2. In step S3, the forward osmosis phenomenon is continued by supplying the wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid to the permeate flow passage of the NF membrane module 11. In the present embodiment, permeated water discharged from the NF membrane module 11 as wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid is supplied from the tank 32 to the permeated water flow path of the NF membrane module 11.

Also in this embodiment, it is possible to prevent the permeated water from being depleted and the forward osmosis phenomenon to be stopped. Further, according to this embodiment, it is possible to prevent the permeated water from being depleted and the water from being lost from the pores of the separation membrane. As a result, it is possible to prevent the separation membrane from becoming hydrophobic and, in turn, to prevent deterioration of the performance of the separation membrane.

In the present embodiment, the wash water includes the permeated water discharged from the NF membrane module 11. That is, the cleaning water used for cleaning the NF membrane module 11 is self-supplied by the water treatment system 200. It is economical because it is not necessary to supply the wash water from the outside of the water treatment system 200. However, the wash water may be supplied from the outside of the water treatment system 200.

Next, in step S4, it is determined whether or not a predetermined time has elapsed from the start of the cleaning operation. As the forward osmosis phenomenon progresses, the osmotic pressure gradually decreases in the vicinity of the surface of the separation membrane in the raw water channel, and the osmotic pressure difference decreases. As a result, the forward osmosis phenomenon stops.

After allowing the high osmotic pressure liquid to stand still in the raw water flow path for a predetermined time, in step S5, the supply of the high osmotic pressure liquid to the raw water flow path is restarted and the high osmotic pressure liquid is discharged from the raw water flow path. The high osmotic pressure liquid contains a fouling substance which is separated from the NF membrane by the forward osmosis phenomenon. A high cleaning effect can be expected by removing the fouling substance by flushing.

The high osmotic pressure liquid discharged from the NF membrane module 11 is returned to, for example, the flow path of raw water or the tank of raw water. That is, the high osmotic pressure liquid used for cleaning the NF membrane of the NF membrane module 11 may be mixed with the raw water and retreated by the water treatment system 200, or may be treated by another treatment device such as an evaporator. Good. When the high osmotic pressure liquid is mixed with the raw water to be reprocessed by the water treatment system 200, it is economical because no special treatment device is required. When the high osmotic pressure liquid does not contain a special chemical, the separation membrane such as the RO membrane and the NF membrane is not likely to be damaged.

According to the method of this embodiment, the upstream separation membrane module (NF membrane module 11) is washed with the high osmotic pressure liquid generated in the downstream treatment device (RO membrane module 12). The hyperosmotic liquid is self-contained by the water treatment system 200. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. Since it is not necessary to use a cleaning agent such as an alkali, an acid or a special chemical, it is possible to reduce the cost spent for cleaning the separation membrane.

(Embodiment 3)
FIG. 6 shows the configuration of the water treatment system 300 according to the third embodiment. The water treatment system 300 includes the NF membrane module 11, the electrodialysis device 13, and the flow path 28. The NF membrane module 11 and the electrodialysis device 13 are connected in series in this order. The flow path 28 connects the permeated water outlet of the NF membrane module 11 and the inlet of the electrodialysis device 13. Raw water is supplied to the NF membrane module 11 and filtered in the NF membrane module 11. The permeated water discharged from the NF membrane module 11 is processed in the electrodialysis device 13.

The NF membrane module 11 is an example of an upstream separation membrane module. The electrodialysis device 13 is an example of a downstream processing device. The electrodialysis device 13 processes the permeated water discharged from the NF membrane module 11.

The water treatment system 300 further includes a flow path 29 and a tank 34. The tank 34 is connected to the permeate outlet of the NF membrane module 11 by the flow path 29. In this embodiment, the flow path 29 is branched from the flow path 28. The permeated water discharged from the NF membrane module 11 is stored in the tank 34.

The water treatment system 300 further includes a flow path 40 and a tank 35. The tank 35 is connected to the concentrated water outlet of the electrodialysis device 13 by a flow path 40. The concentrated water discharged from the electrodialysis device 13 is stored in the tank 35.

The water treatment system 300 further includes a cleaning channel 41. The cleaning flow channel 41 is a flow channel that guides a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the NF membrane module 11 from the electrodialysis device 13 to the raw water flow channel of the NF membrane module 11. When performing the washing operation in the water treatment system 300, the high osmotic pressure liquid is introduced into the raw water flow path of the NF membrane module 11 to cause a normal osmosis phenomenon in the NF membrane of the NF membrane module 11. As a result, the NF film of the NF film module 11 is washed.

In the present embodiment, the hyperosmotic liquid contains concentrated water produced by the electrodialysis device 13. That is, the high osmotic pressure liquid used for cleaning the NF membrane module 11 is self-supplied by the water treatment system 300. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. The hyperosmotic liquid may include only concentrated water produced by the electrodialysis device 13. The high osmotic pressure liquid may contain other liquids, other additives, and the like, as long as they do not bring about a great disadvantage that economic efficiency is significantly deteriorated. The hyperosmotic liquid may include, for example, a cleaning agent for cleaning the separation membrane. Further, salts such as NaCl and Na ₂ SO ₄ generated in the water treatment system 300 may be added to increase the osmotic pressure of the high osmotic pressure liquid.

In the present embodiment, the cleaning flow channel 41 connects the tank 35 and the high osmotic pressure liquid inlet of the NF membrane module 11. The cleaning channel 41 may be a channel branched from the channel 40 or may be a channel directly connected to the tank 35.

The electrodialysis device 13 is a membrane separation device including an ion exchange membrane and an electrode pair.

Next, the operation of the water treatment system 300 will be described.

[Normal operation]
During normal operation, raw water is supplied to the raw water inlet of the NF membrane module 11. Raw water is filtered by the NF membrane module 11. Along with this, concentrated water and permeated water are generated in the NF membrane module 11. The concentrated water is processed by, for example, an evaporator. The residue contains, for example, a salt of a divalent ion such as sulfate ion. The permeated water is guided to the electrodialysis device 13 through the flow path 28. Part of the permeated water is guided to the tank 34 through the flow path 29 and temporarily stored in the tank 34.

The electrodialysis device 13 processes the permeated water discharged from the NF membrane module 11. Along with this, concentrated water and demineralized water are generated in the electrodialysis device 13. Demineralized water is clean water that contains almost no solute and is reused, for example, as industrial water.

The concentrated water discharged from the electrodialysis device 13 is guided to the tank 35 through the flow path 40 and temporarily stored in the tank 35. The concentrated water discharged from the electrodialysis device 13 may be a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the NF membrane module 11. The salt concentration of the concentrated water discharged from the electrodialysis device 13 may be higher than the salt concentration of the raw water to be introduced into the NF membrane module 11. A high osmotic pressure liquid is produced in the electrodialysis device 13. A part of the concentrated water discharged from the electrodialysis device 13 is stored in the tank 35 as a high osmotic pressure liquid and used for cleaning the NF membrane module 11. The rest of the concentrated water discharged from the electrodialysis device 13 is further processed by a processing device such as an evaporator.

The concentrated water discharged from the electrodialysis device 13 is, for example, clean water that contains a high concentration of monovalent ions but is free from dyes, organic substances and COD components. Therefore, the concentrated water discharged from the electrodialysis device 13 can be suitably used as the high osmotic pressure liquid for the washing operation.

[Cleaning operation]
As described in the first and second embodiments, the cleaning operation is performed according to the flowchart shown in FIG. In step S1, the supply of raw water to the NF membrane module 11 is stopped, and the high osmotic pressure liquid is introduced into the raw water flow passage of the NF membrane module 11 through the washing flow passage 41.

Immediately after the start of the cleaning operation, the permeated water channel of the NF membrane module 11 is filled with permeated water. Therefore, the forward osmosis phenomenon occurs based on the difference between the osmotic pressure of the high osmotic pressure liquid and the osmotic pressure of the permeated water, and water moves from the permeated water channel to the raw water channel. As a result, the fouling substance deposited on the NF film floats.

After introducing the high osmotic pressure liquid into the raw water flow path of the NF membrane module 11, the high osmotic pressure liquid is made to stand still in the raw water flow path for a predetermined time in step S2.

The operation of step S3 is executed in parallel with the operation of step S2. In step S3, the forward osmosis phenomenon is continued by supplying the wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid to the permeate flow passage of the NF membrane module 11. In this embodiment, permeated water discharged from the NF membrane module 11 as wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid is supplied from the tank 34 to the permeated water flow path of the NF membrane module 11.

Also in this embodiment, it is possible to prevent the permeated water from being depleted and the forward osmosis phenomenon to be stopped. Further, according to this embodiment, it is possible to prevent the permeated water from being depleted and the water from being lost from the pores of the separation membrane. As a result, it is possible to prevent the separation membrane from becoming hydrophobic and, in turn, to prevent deterioration of the performance of the separation membrane.

In the present embodiment, the wash water includes the permeated water discharged from the NF membrane module 11. That is, the cleaning water used for cleaning the NF membrane module 11 is self-supplied by the water treatment system 300. It is economical because it is not necessary to supply the wash water from the outside of the water treatment system 300. However, the wash water may be supplied from outside the water treatment system 300.

Next, in step S4, it is determined whether or not a predetermined time has elapsed from the start of the cleaning operation. As the forward osmosis phenomenon progresses, the osmotic pressure gradually decreases in the vicinity of the surface of the separation membrane in the raw water channel, and the osmotic pressure difference decreases. As a result, the forward osmosis phenomenon stops.

After allowing the high osmotic pressure liquid to stand still in the raw water flow path for a predetermined time, in step S5, the supply of the high osmotic pressure liquid to the raw water flow path is restarted and the high osmotic pressure liquid is discharged from the raw water flow path. The high osmotic pressure liquid contains a fouling substance which is separated from the NF membrane by the forward osmosis phenomenon. A high cleaning effect can be expected by removing the fouling substance by flushing.

The high osmotic pressure liquid discharged from the NF membrane module 11 is returned to, for example, the flow path of raw water or the tank of raw water. That is, the high osmotic pressure liquid used for cleaning the NF membrane of the NF membrane module 11 may be mixed with the raw water and retreated by the water treatment system 300, or may be treated by another treatment device such as an evaporator. Good. When a high osmotic pressure liquid is mixed with raw water and reprocessed by the water treatment system 300, it is economical because no special treatment device is required. When the high osmotic pressure liquid does not contain a special chemical, the separation membrane such as the RO membrane and the NF membrane is not likely to be damaged.

According to the method of the present embodiment, the upstream separation membrane module (NF membrane module 11) is washed with the hyperosmotic liquid generated in the downstream treatment device (electrodialysis device 13). The hyperosmotic liquid is self-contained by the water treatment system 300. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. Since it is not necessary to use a cleaning agent such as an alkali, an acid or a special chemical, it is possible to reduce the cost spent for cleaning the separation membrane.

In the present embodiment, an RO membrane module may be used instead of the NF membrane module 11. In this case, the concentrated water of the RO membrane module is guided to the electrodialysis device 13.

(Embodiment 4)
FIG. 7 shows the configuration of the water treatment system 400 according to the fourth embodiment. The water treatment system 400 is a combination of the water treatment system 100 of the first embodiment and the water treatment system 200 of the second embodiment.

The water treatment system 400 includes an RO membrane module 10, an NF membrane module 11, an RO membrane module 12, a channel 20 and a channel 24. The RO membrane module 10, the NF membrane module 11, and the RO membrane module 12 are connected in series in this order. Raw water is supplied to the RO membrane module 10 and filtered in the RO membrane module 10. The concentrated water discharged from the RO membrane module 10 is filtered in the NF membrane module 11. The permeated water discharged from the NF membrane module 11 is filtered in the RO membrane module 12.

The water treatment system 400 further includes a flow path 21, a flow path 25, a flow path 26, a tank 30, a tank 32, and a tank 33. The configurations and functions of these flow paths and tanks are as described in the first and second embodiments.

The water treatment system 400 further includes cleaning channels 23 and 27. The configurations and functions of these flow paths are also as described in the first and second embodiments. In the present embodiment, the cleaning channel 23 is configured to guide the permeated water stored in the tank 32 to the raw water channel of the RO membrane module 10 as a high osmotic pressure liquid. The cleaning flow path 23 may be configured to guide the permeated water stored in the tank 33 to the raw water flow path of the RO membrane module 10 as a high osmotic pressure liquid.

According to this embodiment, the effects described in the first and second embodiments can be obtained. By treating the raw water with the plurality of RO membrane modules 10 and 12, the amount of concentrated water that finally occurs can be significantly reduced. This is very significant when the water treatment system 400 is a ZLD system. This is because the energy consumed in the evaporator can be reduced as the amount of concentrated water finally generated decreases.

Next, the operation of the water treatment system 400 will be described.

[Normal operation]
During normal operation, raw water is supplied to the raw water inlet of the RO membrane module 10. Raw water is filtered by the RO membrane module 10. Along with this, concentrated water and permeated water are generated in the RO membrane module 10. The permeated water is guided to the tank 30 through the flow path 21, and is temporarily stored in the tank 30. The permeated water is clean water containing almost no solute and is reused as, for example, industrial water. The concentrated water is guided to the NF membrane module 11 through the flow path 20.

The NF membrane module 11 further filters the concentrated water discharged from the RO membrane module 10. Along with this, concentrated water and permeated water are generated in the NF membrane module 11. The concentrated water is processed by, for example, an evaporator. The residue contains, for example, a salt of a divalent ion such as sulfate ion. The permeated water is guided to the RO membrane module 12 through the flow path 24. A part of the permeated water is guided to the tank 32 through the flow path 25 and temporarily stored in the tank 32.

The RO membrane module 12 further filters the permeated water discharged from the NF membrane module 11. Along with this, concentrated water and permeated water are generated in the RO membrane module 12.

The concentrated water discharged from the RO membrane module 12 is guided to the tank 33 through the flow path 26 and temporarily stored in the tank 33. The permeated water is clean water containing almost no solute and is reused as, for example, industrial water.

[Cleaning operation]
The cleaning operation is an operation for removing the fouling substances deposited on the RO film of the RO film module 10 and the NF film of the NF film module 11. As described in the first and second embodiments, the cleaning operation is performed according to the flowchart shown in FIG. In step S1, the supply of raw water to the RO membrane module 10 is stopped, and the high osmotic pressure liquid is introduced into the raw water passage of the RO membrane module 10 through the washing passage 23. The high osmotic pressure liquid is introduced into the raw water flow path of the NF membrane module 11 through the cleaning flow path 27.

After introducing the high osmotic pressure liquid into the raw water flow path of the RO membrane module 10 and the raw water flow path of the NF membrane module 11, the high osmotic pressure liquid is allowed to stand still in the raw water flow path for a predetermined time in step S2.

The operation of step S3 is executed in parallel with the operation of step S2. In step S3, the normal osmosis phenomenon is continued by supplying the wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid to the permeate flow channels of the RO membrane module 10 and the NF membrane module 11. In the present embodiment, permeated water discharged from the RO membrane module 10 as wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid is supplied from the tank 30 to the permeated water channel of the RO membrane module 10. The permeated water discharged from the NF membrane module 11 as wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid is supplied from the tank 32 to the permeated water flow path of the NF membrane module 11.

Also in this embodiment, it is possible to prevent the permeated water from being depleted and the forward osmosis phenomenon to be stopped. Further, according to this embodiment, it is possible to prevent the permeated water from being depleted and the water from being lost from the pores of the separation membrane. As a result, it is possible to prevent the separation membrane from becoming hydrophobic and, in turn, to prevent deterioration of the performance of the separation membrane.

Also in this embodiment, the cleaning water used for cleaning the RO membrane module 10 and the NF membrane module 11 is self-supplied by the water treatment system 400. It is economical because it is not necessary to supply the wash water from outside the water treatment system 400. However, the wash water may be supplied from outside the water treatment system 400.

Next, in step S4, it is determined whether or not a predetermined time has elapsed from the start of the cleaning operation. As the forward osmosis phenomenon progresses, the osmotic pressure gradually decreases in the vicinity of the surface of the separation membrane in the raw water channel, and the osmotic pressure difference decreases. As a result, the forward osmosis phenomenon stops.

After allowing the high osmotic pressure liquid to stand still in the raw water flow path for a predetermined time, in step S5, the supply of the high osmotic pressure liquid to the raw water flow path is restarted and the high osmotic pressure liquid is discharged from the raw water flow path. The high osmotic pressure liquid contains a fouling substance separated from the RO film or the NF film by the forward osmosis phenomenon. A high cleaning effect can be expected by removing the fouling substance by flushing.

The high osmotic pressure liquid discharged from the RO membrane module 10 and the NF membrane module 11 is returned to, for example, the flow path of raw water or the tank of raw water. That is, the high osmotic pressure liquid used for cleaning the RO membrane module 10 and the NF membrane module 11 may be mixed with the raw water and retreated by the water treatment system 400, or treated by another treatment device such as an evaporator. May be done. When the high osmotic pressure liquid is mixed with the raw water and retreated by the water treatment system 400, it is economical because no special treatment device is required. When the high osmotic pressure liquid does not contain a special chemical, the separation membrane such as the RO membrane and the NF membrane is not likely to be damaged.

According to the method of the present embodiment, the upstream separation membrane module (RO membrane module 10 or NF membrane module 11 is used by using the hyperosmotic liquid generated in the downstream treatment device (NF membrane module 11 or RO membrane module 12). ) Is washed. The hyperosmotic liquid is self-contained by the water treatment system 400. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. Since it is not necessary to use a cleaning agent such as an alkali, an acid, or a special chemical, it is possible to reduce the cost for cleaning the separation membrane.

(Embodiment 5)
FIG. 8 shows the configuration of the water treatment system 500 according to the fifth embodiment. The water treatment system 500 corresponds to a modification of the water treatment system 400 of the fourth embodiment.

The water treatment system 500 includes an RO membrane module 10, an RO membrane module 12, an NF membrane module 11, a flow channel 20a and a flow channel 20b. The RO membrane module 10, the RO membrane module 12, and the NF membrane module 11 are connected in series in this order. The flow path 20a connects the concentrated water outlet of the RO membrane module 10 and the raw water inlet of the RO membrane module 12. The flow path 20b connects the concentrated water outlet of the RO membrane module 12 and the raw water inlet of the NF membrane module 11. Raw water is supplied to the RO membrane module 10 and filtered in the RO membrane module 10. The concentrated water discharged from the RO membrane module 10 is filtered in the RO membrane module 12. The concentrated water discharged from the RO membrane module 12 is filtered in the NF membrane module 11.

The water treatment system 500 further includes a flow path 21, a flow path 22, a tank 30, and a tank 31. The configurations and functions of these flow paths and tanks are as described in the first embodiment.

The water treatment system 500 further includes a flow path 42 and a tank 36. The tank 36 is connected to the permeate outlet of the RO membrane module 12 by the flow path 42. In this embodiment, the permeated water discharged from the RO membrane module 12 is stored in the tank 36.

The water treatment system 500 further includes a cleaning flow path 23. The configuration and function of the cleaning flow path 23 are as described in the first embodiment. The cleaning flow path 23 may be configured to guide the permeated water stored in the tank 31 to the raw water flow path of the RO membrane module 10 as a high osmotic pressure liquid.

The water treatment system 500 further includes a cleaning channel 44. The cleaning flow channel 44 is a flow channel that guides a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the RO membrane module 12 from the NF membrane module 11 to the raw water flow channel of the RO membrane module 12. When performing a cleaning operation in the water treatment system 500, a high osmotic pressure liquid is introduced into the raw water flow path of the RO membrane module 12 to cause a forward osmosis phenomenon in the RO membrane of the RO membrane module 12. As a result, the RO membrane of the RO membrane module 12 is cleaned.

In this embodiment, the high osmotic pressure liquid contains the permeated water discharged from the NF membrane module 11. That is, the high osmotic pressure liquid used for cleaning the RO membrane modules 10 and 12 is self-supplied by the water treatment system 500. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. The high osmotic pressure liquid may contain only the permeated water discharged from the NF membrane module 11. The high osmotic pressure liquid may contain other liquids, other additives, and the like, as long as they do not bring about a great disadvantage that economic efficiency is significantly deteriorated. The hyperosmotic liquid may include, for example, a cleaning agent for cleaning the separation membrane. Further, salts such as NaCl and Na ₂ SO ₄ produced in the water treatment system 500 may be added to increase the osmotic pressure of the high osmotic pressure liquid.

In the present embodiment, the cleaning flow path 44 connects the tank 31 and the high osmotic pressure liquid inlet of the RO membrane module 12. The cleaning channel 44 may be a channel branched from the channel 22, or may be a channel directly connected to the tank 31.

Next, the operation of the water treatment system 500 will be described.

[Normal operation]
During normal operation, raw water is supplied to the raw water inlet of the RO membrane module 10. Raw water is filtered by the RO membrane module 10. Along with this, concentrated water and permeated water are generated in the RO membrane module 10. The permeated water is guided to the tank 30 through the flow path 21, and is temporarily stored in the tank 30. The permeated water is clean water containing almost no solute and is reused as, for example, industrial water. The concentrated water is guided to the RO membrane module 12 through the flow path 20a.

The RO membrane module 12 further filters the concentrated water discharged from the RO membrane module 10. Along with this, concentrated water and permeated water are generated in the RO membrane module 12. The permeated water is guided to the tank 36 through the flow path 42 and temporarily stored in the tank 36. The permeated water is clean water containing almost no solute and is reused as, for example, industrial water. The concentrated water is guided to the NF membrane module 11 through the flow path 20b.

The NF membrane module 11 further filters the concentrated water discharged from the RO membrane module 12. Along with this, concentrated water and permeated water are generated in the NF membrane module 11.

The permeated water discharged from the NF membrane module 11 is guided to the tank 31 through the flow path 22 and temporarily stored in the tank 31.

The permeated water discharged from the NF membrane module 11 is, for example, clean water that contains a high concentration of monovalent ions but is free from dyes, organic substances and COD components. Therefore, the permeated water discharged from the NF membrane module 11 can be suitably used as the high osmotic pressure liquid for the cleaning operation.

[Cleaning operation]
The cleaning operation is an operation for removing the fouling substances deposited on the RO membranes of the RO membrane modules 10 and 12. The cleaning operation is performed according to the flowchart shown in FIG. In step S1, the supply of raw water to the RO membrane module 10 is stopped, and the high osmotic pressure liquid is introduced into the raw water passage of the RO membrane module 10 through the washing passage 23. The high osmotic pressure liquid is introduced into the raw water flow path of the RO membrane module 12 through the cleaning flow path 44.

After introducing the high osmotic pressure liquid into the raw water flow passages of the RO membrane modules 10 and 12, in step S2, the high osmotic pressure liquid is made to stand still in the raw water flow passage for a predetermined time.

The operation of step S3 is executed in parallel with the operation of step S2. In step S3, the forward osmosis phenomenon is continued by supplying the wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid to the permeate water flow paths of the RO membrane modules 10 and 12. In the present embodiment, permeated water discharged from the RO membrane module 10 as wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid is supplied from the tank 30 to the permeated water channel of the RO membrane module 10. Permeate discharged from the RO membrane module 12 as wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid is supplied from the tank 36 to the permeate flow passage of the RO membrane module 12.

Also in this embodiment, it is possible to prevent the permeated water from being depleted and the forward osmosis phenomenon to be stopped. Further, according to this embodiment, it is possible to prevent the permeated water from being depleted and the water from being lost from the pores of the separation membrane. As a result, it is possible to prevent the separation membrane from becoming hydrophobic and, in turn, to prevent deterioration of the performance of the separation membrane.

Also in this embodiment, the cleaning water used for cleaning the RO membrane modules 10 and 12 is self-supplied by the water treatment system 500. It is economical because it is not necessary to supply the wash water from the outside of the water treatment system 500. However, the wash water may be supplied from outside the water treatment system 500.

Next, in step S4, it is determined whether or not a predetermined time has elapsed from the start of the cleaning operation. As the forward osmosis phenomenon progresses, the osmotic pressure gradually decreases in the vicinity of the surface of the separation membrane in the raw water channel, and the osmotic pressure difference decreases. As a result, the forward osmosis phenomenon stops.

After allowing the high osmotic pressure liquid to stand still in the raw water flow path for a predetermined time, in step S5, the supply of the high osmotic pressure liquid to the raw water flow path is restarted and the high osmotic pressure liquid is discharged from the raw water flow path. The high osmotic pressure liquid contains a fouling substance separated from the RO membrane by the forward osmosis phenomenon. A high cleaning effect can be expected by removing the fouling substance by flushing.

The high osmotic pressure liquid discharged from the RO membrane modules 10 and 12 is returned to, for example, the flow path of raw water or the tank of raw water. That is, the high osmotic pressure liquid used for cleaning the RO membrane modules 10 and 12 may be mixed with raw water and retreated in the water treatment system 500, or may be treated in another treatment device such as an evaporator. Good. When the high osmotic pressure liquid is mixed with the raw water and reprocessed by the water treatment system 500, it is economical because no special treatment device is required. When the high osmotic pressure liquid does not contain a special chemical, the separation membrane such as the RO membrane and the NF membrane is not likely to be damaged.

According to the method of the present embodiment, the upstream separation membrane module (RO membrane modules 10 and 12) is washed using the hyperosmotic liquid generated in the downstream treatment device (NF membrane module 11). The hyperosmotic liquid is self-contained by the water treatment system 500. It is economical because there is no need to supply the hyperosmotic liquid from outside the system. Since it is not necessary to use a cleaning agent such as an alkali, an acid, or a special chemical, it is possible to reduce the cost for cleaning the separation membrane.

(Embodiment 6)
FIG. 9 shows the configuration of the water treatment system 600 according to the sixth embodiment. The water treatment system 600 includes the configuration of the water treatment system 400 of the fourth embodiment.

The water treatment system 600 further includes a tank 38 in addition to the components of the water treatment system 400. The tank 38 stores waste water which is untreated raw water.

The water treatment system 600 further includes a pretreatment device 14, an RO membrane module 15, and a hardness removing device 16.

Untreated wastewater is supplied from the tank 38 to the pretreatment device 14 through the flow path 50. The pretreatment device 14 is composed of, for example, a settling tank and plays a role of removing solid components. Raw water treated in the pretreatment device 14 is supplied to the RO membrane module 15 through the flow path 51. The pretreatment device 14 may include a separation membrane such as an NF membrane or a UF membrane.

The RO membrane module 15 may have the same structure as the RO membrane module 10 described above.

The water treatment system 600 further includes a flow path 54 and a tank 37. The tank 37 is connected to the permeate outlet of the RO membrane module 15 by the flow path 54. The permeated water discharged from the RO membrane module 15 is stored in the tank 37.

The water treatment system 600 further includes a cleaning channel 45. The cleaning flow channel 45 is a flow channel that guides a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the RO membrane module 15 from the downstream treatment device to the raw water flow channel of the RO membrane module 15. When performing the washing operation in the water treatment system 600, the high osmotic pressure liquid is introduced into the raw water flow path of the RO membrane module 15 to cause the forward osmosis phenomenon in the RO membrane of the RO membrane module 15. As a result, the RO membrane of the RO membrane module 15 is cleaned.

When the cleaning operation is performed, permeated water discharged from the RO membrane module 15 as cleaning water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid is supplied from the tank 37 to the permeated water flow path of the RO membrane module 15. .. This can prevent the permeated water from being depleted and the forward osmosis phenomenon to stop.

When the upstream separation membrane module is the RO membrane module 15, the downstream treatment device is the NF membrane module 11. In the washing operation, the permeated water discharged from the NF membrane module 11 is supplied as a high osmotic pressure liquid to the raw water flow path of the RO membrane module 15. Specifically, the permeated water discharged from the NF membrane module 11 is supplied from the tank 32 to the raw water flow path of the RO membrane module 15.

The concentrated water discharged from the RO membrane module 12 may be supplied to the RO membrane module 10 and/or the RO membrane module 15 as a hyperosmotic liquid. As opposed to RO membrane module 10, RO membrane module 12 can be a downstream processing unit. In contrast to RO membrane module 15, RO membrane module 12 can be a downstream processing unit.

The concentrated water discharged from the RO membrane module 15 is supplied to the hardness removing device 16 through the flow path 52. The hardness removing device 16 is a device for removing hardness components such as calcium and magnesium. The structure of the hardness removing device 16 is not particularly limited. The hardness removing device 16 may be configured to remove the hardness component with an ion exchange resin, or may be configured to precipitate and remove the hardness component by adding an alkaline agent to the raw water.

The hardness removing device 16 may be included in the pretreatment device 14.

The wastewater treated by the hardness removing device 16 is supplied to the RO membrane module 10 as raw water through the flow path 53.

The water treatment system 600 further includes the electrodialysis device 13. The electrodialysis device 13 processes the concentrated water discharged from the RO membrane module 12.

Water treatment system 600 further comprises evaporators 17 and 18. The evaporator 17 heats the concentrated water discharged from the NF membrane module 11 to evaporate the water. As the residue, salts of divalent ions such as sulfate ions are mainly obtained. The evaporator 18 heats the concentrated water discharged from the electrodialysis device 13 to evaporate water. As the residue, a salt of monovalent ion such as chloride ion is mainly obtained.

The water treatment system 600 further includes a drainage channel 55. The drainage channel 55 is a channel that connects the high osmotic pressure liquid outlet of each separation membrane module and the tank 38. The high osmotic pressure liquid used in the cleaning operation of the RO membrane module 15, the RO membrane module 10 and the NF membrane module 11 is collected in the tank 38 through the drainage channel 55 and mixed with untreated wastewater. This is economical because no special device for treating the hyperosmotic liquid used in the washing operation is required.

Also in this embodiment, the cleaning operation is performed according to the flowchart shown in FIG.

The hyperosmotic liquid and wash water used in the wash run are all self-contained by the water treatment system 600. It is economical because there is no need to supply high osmotic pressure liquid and wash water from outside the system.

(Embodiment 7)
FIG. 10 shows the configuration of the water treatment system 700 according to the seventh embodiment. The water treatment system 700 includes the configuration of the water treatment system 300 of the third embodiment and the configuration of the water treatment system 500 of the fifth embodiment.

The water treatment system 700 further includes a tank 38. The tank 38 stores waste water which is untreated raw water.

The water treatment system 700 further includes a pretreatment device 14, an RO membrane module 15, and a hardness removing device 16. These configurations and functions are as described in the sixth embodiment.

The water treatment system 700 further includes a flow path 54 and a tank 37. These configurations and functions are as described in the sixth embodiment.

The water treatment system 700 further includes evaporators 17 and 18. These configurations and functions are as described in the sixth embodiment.

The water treatment system 700 further includes cleaning channels 46, 47 and 48. The cleaning channel 46 is a channel that guides a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the RO membrane module 15 from the downstream treatment device to the raw water channel of the RO membrane module 15. In the present embodiment, the downstream processing device for the RO membrane module 15 is the NF membrane module 11. In the cleaning operation, the permeated water discharged from the NF membrane module 11 is supplied to the raw water flow path of the RO membrane module 15 as a high osmotic pressure liquid. Specifically, the permeated water discharged from the NF membrane module 11 is supplied from the tank 34 to the raw water flow path of the RO membrane module 15.

The cleaning channel 47 is a channel that guides a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the RO module membrane 12 from the downstream treatment device to the raw water channel of the RO membrane module 12. The cleaning flow channel 48 is a flow channel that guides a high osmotic pressure liquid having an osmotic pressure higher than the osmotic pressure of the permeated water of the NF membrane module 11 from the downstream treatment device to the raw water flow channel of the NF membrane module 11. In this embodiment, the downstream treatment device for the NF membrane module 11 and the RO membrane module 12 is the electrodialysis device 13. In the washing operation, the concentrated water discharged from the electrodialysis device 13 is supplied to the raw water flow paths of the NF membrane module 11 and the RO membrane module 12 as a high osmotic pressure liquid. Specifically, the concentrated water discharged from the electrodialysis device 13 is supplied from the tank 35 to the raw water flow paths of the NF membrane module 11 and the RO membrane module 12.

The concentrated water discharged from the electrodialysis device 13 may be supplied to the RO membrane module 10 and/or the RO membrane module 15 as a hyperosmotic liquid. With respect to the RO membrane module 10, the electrodialysis device 13 can be a downstream treatment device. With respect to the RO membrane module 15, the electrodialysis device 13 can be a downstream treatment device. The permeated water discharged from the NF membrane module 11 may be supplied to the RO membrane module 12 as a high osmotic pressure liquid. With respect to the RO membrane module 12, the NF membrane module 11 can be a downstream processing device.

Also in this embodiment, the cleaning operation is performed according to the flowchart shown in FIG.

The hyperosmotic liquid and wash water used in the wash run are all self-contained by the water treatment system 700. It is economical because there is no need to supply high osmotic pressure liquid and wash water from outside the system.

The technique of the present invention can be applied to water treatment such as wastewater treatment. The technique of the present invention is particularly useful for ZLD systems.

10, 12, 15 RO membrane module 11 NF membrane module 13 Electrodialysis device 14 Pretreatment device 16 Hardness removal device 17, 18 Evaporator 20, 21, 22, 24, 25, 26, 28, 29, 40, 42, 50 , 51, 52, 53, 54 Flow paths 20a, 20b Flow paths 23, 27, 41, 44, 45, 46, 47, 48 Cleaning flow paths 30, 31, 32, 33, 34, 35, 36, 37, 38 Tank 55 Drainage channel 59 Container 60 RO membrane element 61 Water collection pipe 61h Through hole 62 RO membrane 63 Raw water spacer 64 Permeate spacer 71 Raw water inlet 72 Concentrated water outlet 73 High osmotic pressure liquid inlet 74 High osmotic pressure liquid outlet 75 Permeate outlet 77,78 valve 100,200,300,400,500,600,700 water treatment system

Claims (17)

Filtering raw water with an upstream separation membrane module,
Generating a hyperosmotic liquid having an osmotic pressure higher than the osmotic pressure of the permeate by treating the permeate or the concentrated water discharged from the upstream separation membrane module with a downstream treatment device;
By introducing the high osmotic pressure liquid into the raw water flow path of the upstream separation membrane module to cause a forward osmosis phenomenon in the separation membrane of the upstream separation membrane module, the separation membrane of the upstream separation membrane module is removed. To wash,
A method of operating a water treatment system, including: The downstream treatment device includes a downstream separation membrane module that filters the permeated water or the concentrated water discharged from the upstream separation membrane module,
The method of operating a water treatment system according to claim 1, wherein the high osmotic pressure liquid includes permeated water or concentrated water discharged from the downstream separation membrane module. The upstream separation membrane module includes an RO membrane as the separation membrane,
The downstream separation membrane module includes an NF membrane as a separation membrane, and filters the concentrated water discharged from the upstream separation membrane module,
The method for operating a water treatment system according to claim 2, wherein the high osmotic pressure liquid contains the permeated water discharged from the downstream separation membrane module. The upstream separation membrane module includes an NF membrane as the separation membrane,
The downstream separation membrane module includes an RO membrane as a separation membrane, and filters the permeated water discharged from the upstream separation membrane module,
The method for operating a water treatment system according to claim 2, wherein the high osmotic pressure liquid includes the concentrated water discharged from the downstream separation membrane module. The method for operating a water treatment system according to claim 3, wherein the NF membrane is an NF membrane capable of selectively separating monovalent ions and divalent ions. The downstream processing device includes an electrodialysis device,
The method for operating a water treatment system according to claim 1, wherein the hyperosmotic liquid contains concentrated water produced by the electrodialysis device. 7. The forward osmosis phenomenon is continued by supplying wash water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid to the permeate flow passage of the upstream separation membrane module. The method for operating the water treatment system according to the item. The method for operating a water treatment system according to claim 7, wherein the wash water includes permeated water discharged from the upstream separation membrane module. When cleaning the separation membrane of the upstream separation membrane module, after introducing the high osmotic pressure liquid into the raw water flow path of the upstream separation membrane module, the high osmotic pressure liquid is passed through the raw water flow path for a predetermined time. The method for operating the water treatment system according to any one of claims 1 to 8, which is caused to stand still in a room. The method for operating a water treatment system according to claim 9, wherein the high osmotic pressure liquid is allowed to stand still in the raw water flow passage for the predetermined time, and then the high osmotic pressure liquid is discharged from the raw water flow passage. 11. The method according to claim 1, further comprising mixing the high osmotic pressure liquid used for cleaning the separation membrane of the upstream separation membrane module with the raw water and reprocessing the water in the water treatment system. The method for operating the water treatment system according to the item. An upstream separation membrane module,
A downstream treatment device for producing a hyperosmotic liquid having an osmotic pressure higher than the osmotic pressure of the permeate by treating the permeate or the concentrated water discharged from the upstream separation membrane module;
A cleaning flow channel that guides the high osmotic pressure liquid from the downstream treatment device to the raw water flow channel of the upstream separation membrane module,
Equipped with
By introducing the high osmotic pressure liquid into the raw water flow path of the upstream separation membrane module to cause a forward osmosis phenomenon in the separation membrane of the upstream separation membrane module, the separation membrane of the upstream separation membrane module is removed. Water treatment system to wash. The downstream treatment device includes a downstream separation membrane module that filters permeated water or concentrated water discharged from the upstream separation membrane module,
The water treatment system according to claim 12, wherein the high osmotic pressure liquid includes permeated water or concentrated water discharged from the downstream separation membrane module. The upstream separation membrane module includes an RO membrane as the separation membrane,
The downstream separation membrane module includes an NF membrane as a separation membrane, and filters the concentrated water discharged from the upstream separation membrane module,
The water treatment system according to claim 13, wherein the hyperosmotic liquid contains the permeated water discharged from the downstream separation membrane module. The upstream separation membrane module includes an NF membrane as the separation membrane,
The downstream separation membrane module includes an RO membrane as a separation membrane, and filters the permeated water discharged from the upstream separation membrane module,
The water treatment system according to claim 13, wherein the hyperosmotic liquid contains the concentrated water discharged from the downstream separation membrane module. The downstream processing device includes an electrodialysis device,
The water treatment system according to claim 12, wherein the hyperosmotic liquid contains concentrated water produced by the electrodialysis device. Further comprising a tank for storing the permeated water discharged from the upstream separation membrane module,
When the high osmotic pressure liquid is introduced into the raw water flow path of the upstream separation membrane module through the cleaning flow path, the upstream of the cleaning water having an osmotic pressure lower than the osmotic pressure of the high osmotic pressure liquid The water treatment system according to any one of claims 12 to 16, wherein the permeated water discharged from the separation membrane module is supplied from the tank to a permeated water flow path of the upstream separation membrane module.

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