JP6648695B2 - Operating method of semipermeable membrane separation device - Google Patents

Description

  The present invention relates to a method for operating a semipermeable membrane separation device for obtaining low-concentration permeate as production water using raw water such as seawater, river water containing salt, groundwater, lake water, and wastewater treatment water. More specifically, the present invention relates to a method for operating a semipermeable membrane separation device capable of appropriately maintaining the water permeability and the blocking performance of a semipermeable membrane, and achieving both energy saving and production water quality.

  In recent years, the depletion of water resources has become serious, and utilization of water resources that have not been used until now is being studied. In particular, attention has been focused on technologies for producing drinking water from seawater that was most familiar and could not be used as it is, so-called "seawater desalination", and also on reuse technology for purifying sewage wastewater and desalinating treated water. ing.

  Conventionally, seawater desalination has been put to practical use centering on the evaporation method in the Middle East where water resources are extremely small and heat resources by oil are very abundant. On the other hand, in regions other than the Middle East, where heat sources are not abundant, reverse osmosis methods with high energy efficiency are adopted.Recently, improvements in reliability and cost reductions due to technological advances in reverse osmosis methods have progressed, and in many regions including the Middle East, , A reverse osmosis seawater desalination plant has been constructed and is showing worldwide expansion.

  Wastewater reuse has begun to be applied to inland and coastal urban and industrial areas where there is no freshwater source or where discharges are restricted due to drainage regulations. In particular, Singapore, an island nation with a scarce water source, responds to water shortages by treating domestically generated sewage, storing it without releasing it into the sea, and regenerating it to a level that can be drunk with reverse osmosis membranes.

  Reverse osmosis, which is applied to such seawater desalination and wastewater reuse, uses desalinated water by passing water containing solutes such as salts through a semipermeable membrane at a pressure higher than the osmotic pressure. It is manufactured. This technology can be used, for example, to obtain drinking water from seawater, brackish water, water containing harmful substances, and has also been used in the production of industrial ultrapure water, wastewater treatment, and recovery of valuable resources. .

  In order to stably operate a desalination device using a reverse osmosis membrane, pretreatment according to the quality of raw water to be taken is required. If the pretreatment is insufficient, the reverse osmosis membrane may be degraded or fouled (fouling of the membrane surface), and stable operation tends to be difficult. In particular, when a chemical substance that degrades the reverse osmosis membrane enters the reverse osmosis membrane, it may fall into a fatal situation that cannot be recovered even by washing. That is, the functional layer of the reverse osmosis membrane (the portion that exhibits the reverse osmosis function) is decomposed, and the performance of separating water and solute, in other words, the ability to prevent solute is reduced.

  When a reverse osmosis membrane is used for applications such as seawater desalination and wastewater reuse, it is very difficult to prevent 100% of the functional layer of such a reverse osmosis membrane from being decomposed. The mainstream polyamide is easily oxidized and deteriorated (Non-Patent Document 1). In addition, the functional layer is likely to be decomposed when exposed to a strong acid or alkali although having some durability.

When such decomposition occurs, in the case of a semi-permeable membrane having a general anion charge as a reverse osmosis membrane for water treatment, the inorganic electrolyte which can be prevented by the charge exclusion effect due to the anion charge is more separated than the separated electrolyte. This has a large adverse effect on the removal of neutral molecules, and particularly the rejection of neutral molecules is poor. Specifically, the water quality of silica, boron, saccharides and the like not dissociated in the neutral region becomes remarkable.
Reverse osmosis membranes that have lost the required blocking performance usually have to be replaced with new ones, which naturally leads to an increase in processing costs.

For this reason, technology for recovering the blocking performance of the reverse osmosis membrane has been developed for many years, a method of contacting and reacting a vinyl polymer (Patent Documents 1 and 2), and contacting polyethylene glycol with the reverse osmosis membrane. (Patent Documents 3 and 4) to increase the rejection rate of nonionic solutes by contacting a nonionic surfactant with a reverse osmosis membrane having an anion charge with an increased permeation flux. (Patent Document 5), a method of contacting iodine and / or an iodine compound having an oxidation-reduction potential of 300 mV or more (Patent Document 6), contact with a strong mineral acid aqueous solution such as phosphoric acid, phosphorous acid, sulfuric acid, etc. to raise the temperature After that, a number of methods for restoring the blocking performance of reverse osmosis membranes and a restoring agent therefor have been proposed, such as a method of contacting with a blocking performance improver such as hydrolyzable tannic acid (Patent Document 6). That.
However, these inhibition performance recovery processes have various technical problems.

  That is, depending on the type and state of the reverse osmosis membrane (dirt, deterioration), the processing environment such as water temperature, and the conditions for performing the processing (temperature, concentration, processing time, etc. of the processing solution), the processing effect of the inhibition performance improvement changes, The reduction in water permeability, which is a side effect of the inhibition performance improvement processing, also changes. In addition, the effect of maintaining the long-term performance after the rejection rate is improved varies, and the water freshness operation after the rejection performance improvement treatment often has insufficient water quality, insufficient operating pressure, and difficulties.

  In large-scale seawater desalination and sewage recycling plants that have been rapidly constructed and started operating since the 2000s, many reverse osmosis membranes are used, and raw water in the natural environment such as seawater is treated. Even if the pretreatment is performed, the reverse osmosis membrane is operated under the influence of the weather, the natural environment, the season, the tide, the red tide, and the like. That is, the state of the reverse osmosis membrane is various even in the same plant, and the technical subjects are also various.

  Further, in order to improve the inhibition performance, after the normal fresh water treatment is once stopped, the raw water to be treated at the time of operation is replaced with the inhibition performance improver through a chemical cleaning line. For this reason, the operating efficiency is reduced, the labor is complicated, and after the treatment is completed, the final effect is not understood unless the water to be treated is passed again to measure the inhibition performance and the water permeability under normal operating conditions. There are many problems, such as no.

  In order to solve the effects on the processing effect due to the difference in the state of the reverse osmosis membrane with respect to these problems, for example, as shown in Patent Document 8, after the reverse osmosis membrane is washed with a chemical solution, the inhibition performance improving treatment is performed. Is generally applied. Further, as shown in Patent Document 9, a pretreatment has been proposed in which the substrate is washed with high-temperature water and then contacted with an inhibitory performance improving agent.

As a method of judging the effect of the inhibition performance improving treatment, a method of adding a substance serving as a label to the inhibition performance improving agent and detecting the concentration of the labeled substance in the permeated water to confirm the treatment effect (Patent Document 10). Proposed.
A method has been proposed in which the supply concentration and the discharge concentration of the rejection performance improver are monitored and the end of the process is determined so that the rejection rate improvement process does not reach saturation and no longer needless wasteful recovery processing time is required. (Patent Document 11).

JP-A-55-114306 JP-A-59-30123 Japanese Patent Application Laid-Open No. 2007-289922 Japanese Patent Application Laid-Open No. 2008-132421 Japanese Patent Application Laid-Open No. 2008-86945 Japanese Patent Application Laid-Open No. 2011-161435 JP-A-2-68102 Japanese Patent Application Laid-Open No. 2008-36522 Japanese Patent Application Laid-Open No. 2009-22888 Japanese Patent Application Laid-Open No. 2008-155123 Japanese Patent Application Publication No. 2008-183488

Tadahiro Uemura et al., Composition of reverse reverse osmosis membranes and changes in membrane structure and membrane separation characteristics due to chlorine degradation, Journal of the Japan Society of Sea Water, Vol. 57, No. 3 (2003) M. Taniguchi et al., Boron Reduction performance of reverse osmosis seawater desalination process, Journal of Membrane Science, 183, 259-267 (2000).

However, in any of the above methods, as a cost of improving the rejection performance, it is inevitable that the water permeability is reduced and the operating pressure is increased.
Therefore, the present invention provides a semipermeable membrane separation device using a semipermeable membrane such as a nanofiltration membrane or a reverse osmosis membrane, which can improve the blocking performance of the semipermeable membrane, particularly the blocking performance of nonionic substances. It is an object of the present invention to provide a method for operating a semipermeable membrane separation apparatus that achieves both energy saving and stable production water quality by efficiently using a performance improvement process and a cleaning process for recovering performance degradation due to fouling.

In order to solve the above problems, the present invention has the following configuration.
(1) A method for operating a semipermeable membrane separation device, which supplies treated water to a semipermeable membrane unit to obtain product water separated and treated on a permeated water side,
By pressurizing and supplying a liquid containing an inhibitory performance enhancer to the treated water side of the semipermeable membrane unit, by contacting and attaching the inhibitory performance enhancer to the membrane surface of the semipermeable membrane in the semipermeable membrane unit. A step A of improving the blocking performance of the semipermeable membrane; and removing and removing the blocking performance improver attached to the semipermeable membrane with a liquid containing a removing agent, thereby improving the water permeability of the semipermeable membrane. Step B for improvement
The operation of a semipermeable membrane separation apparatus, wherein production water is obtained while performing the process intermittently.
(2) At least one selected from a case where the quality of the obtained production water exceeds a reference value, a case where the solute permeability coefficient of the semipermeable membrane exceeds a reference value, and a case where the temperature of the water to be treated exceeds a reference value. In the case of or 1, the step A is performed,
If the operating pressure is higher than the reference value, if the obtained flow rate of the produced water is lower than the reference value, if the pure water permeability coefficient of the semipermeable membrane is lower than the reference value, and if the temperature of the water to be treated is lower than the reference value. The method for operating a semipermeable membrane separation device according to (1), wherein the step B is performed in at least one case selected from the cases where the ratio is lower than the lower limit.
(3) The method of operating the semipermeable membrane separation device according to (1) or (2), wherein the semipermeable membrane is washed before performing at least one of the step A and the step B. .
(4) The operation method of the semipermeable membrane separation device according to (1) or (2), wherein the semipermeable membrane is washed at least simultaneously with at least one of the step A and the step B.
(5) The method for operating a semipermeable membrane separation device according to (4), wherein the semipermeable membrane is washed at the same time as the step B is performed.
(6) The step A is performed during a water temperature rising period in which the temperature of the to-be-treated water is between the lowest water temperature period and the highest water temperature period, and the step B is performed when the temperature of the to-be-treated water is lower than the highest water temperature period. The method for operating the semipermeable membrane separation device according to any one of (1) to (5), wherein the operation is performed in a water temperature drop period that is a water temperature period.
(7) As the liquid containing the inhibitory performance improver in the step A, a liquid obtained by adding the inhibitory performance improver to the water to be treated is used, and the step A is performed while obtaining the production water. An operation method of the semipermeable membrane separation device according to any one of (1) to (6).
(8) The removing performance improver in the step A contains a compound having a polyalkylene glycol chain, and in the step B, (i) the remover is a surfactant; (ii) the remover Contains a compound having at least one selected from a pyridine ring, an alkylamine chain and a piperidine ring; and (iii) the liquid containing the remover exhibits alkalinity, and satisfies at least one selected from the group consisting of: The method for operating the semipermeable membrane separation device according to any one of (1) to (7).
(9) The semipermeable membrane according to any one of (1) to (8), wherein water is transmitted from the permeated water side of the semipermeable membrane unit to the treated water side during the execution of the step B. Operating method of the membrane separation device.
(10) The operation method of the semipermeable membrane separation device according to (9), wherein the permeation of water from the permeated water side to the to-be-treated water side is by forward osmosis.

  According to the operation method of the semipermeable membrane separation device of the present invention, the semipermeable membrane separation device using a semipermeable membrane such as a nanofiltration membrane or a reverse osmosis membrane, the blocking performance of the semipermeable membrane, especially nonionic substances It is possible to produce freshwater while efficiently conserving both energy saving and production water quality by efficiently using the stopping performance improvement process that can improve the stopping performance and the washing process that recovers the performance deterioration due to fouling. Become.

FIG. 1 is an example of a process flow of a semipermeable membrane fresh water generator (semipermeable membrane separation apparatus) to which the method for improving the performance of inhibiting semipermeable membrane (step A) according to the present invention can be applied. FIG. 2 is an example of a process flow of a semipermeable membrane freshwater generator (semipermeable membrane separation device) to which the method for improving the performance of inhibiting semipermeable membrane (step A) according to the present invention can be applied in reverse flow to the semipermeable membrane. is there. FIG. 3 is an example of a process flow of a semipermeable membrane fresh water generator (semipermeable membrane separation apparatus) in which the method for improving the performance of inhibiting semipermeable membrane (step A) according to the present invention can be applied to the semipermeable membrane by reverse flow switching. It is. FIG. 4 is a process flow of a test apparatus used for collecting an example of the method for improving the blocking performance of a semipermeable membrane (step A) according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to these.
The operation method of the semipermeable membrane separation device according to the present invention is an operation method in which water to be treated is supplied to a semipermeable membrane unit to obtain product water separated and treated on a permeate side,
By pressurizing and supplying a liquid containing an inhibitory performance enhancer to the treated water side of the semipermeable membrane unit, by contacting and attaching the inhibitory performance enhancer to the membrane surface of the semipermeable membrane in the semipermeable membrane unit. A step A of improving the blocking performance of the semipermeable membrane; and removing and removing the blocking performance improver attached to the semipermeable membrane with a liquid containing a removing agent, thereby improving the water permeability of the semipermeable membrane. Step B for improvement
It is characterized in that the production water is obtained while intermittently performing.

FIG. 1 shows an example of a semipermeable membrane separation apparatus to which the method for improving semipermeable membrane blocking performance of the present invention can be applied as the step A.
When the semi-permeable membrane fresh water generator shown in FIG. 1 is operated to produce fresh water, the treated water is temporarily stored in the treated water tank 2 through the treated water line 1 and then supplied to the treated water tank 2 as necessary. The liquid is sent to the pretreatment unit 4 by the pump 3 and pretreated.
The pre-treated water passes through an intermediate water tank 5, a pre-treated water supply pump 6, and a security filter 7, and is pressurized by a pressurizing pump 8, and then the permeated water and concentrated water are passed through a semi-permeable membrane unit 9 composed of a semi-permeable membrane module. To separate.
The permeated water is stored in the production water tank 12 via the production water line 10a. The concentrated water is discharged to the outside of the system via the concentrated water discharge line 11a after the pressure energy is recovered by the energy recovery unit 13 as necessary.
During the fresh water producing operation, the supply water valve 16a, the permeate valve 17a, and the concentrate valve 18a are opened, and the supply chemical valve 16b, the permeate chemical valve 17b, and the concentrate chemical valve 18b are closed.

When applying the treatment for improving the inhibition performance in the present invention (Step A) and the treatment for removing and removing the inhibition performance improving agent from the semipermeable membrane using the removing agent (Step B), a chemical liquid circulation line can be used. .
The chemical liquid circulation line includes a chemical liquid tank 15, a chemical liquid supply pump 19, and a chemical liquid addition unit 20a. The chemical liquid is supplied from the chemical liquid supply line 14 to the semipermeable membrane unit 9, and the transmitted chemical liquid (all solutes are blocked depending on the type of the chemical liquid). Therefore, in this case, only the solvent) passes through the permeated water line 10 and the permeated chemical liquid line 10b, and the concentrated chemical liquid that has not passed through passes through the concentrated water line 11 and the concentrated chemical liquid line 11b, and passes through the chemical liquid tank 15 Reflux.

During the process of improving the performance of inhibiting the semipermeable membrane, the supply water valve 16a, the permeate valve 17a, and the concentrate valve 18a are closed, and the supply chemical valve 16b, the permeate chemical valve 17b, and the concentrate chemical valve 18b are open.
The chemical circulation line can also be used for circulating and cleaning the semipermeable membrane using an acid, an alkali, a detergent, or the like.

  In the present invention, a liquid containing an inhibitory performance enhancer is supplied under pressure to the primary side (water to be treated) of the semipermeable membrane in the semipermeable membrane unit, and the inhibitory performance enhancer is applied to the membrane surface of the semipermeable membrane. A step A of improving the blocking performance of the semipermeable membrane by contacting and adhering, and removing the blocking performance improving agent adhering to the semipermeable membrane with a liquid containing a removing agent to thereby remove the semipermeable membrane. The production water is obtained intermittently while performing the process B for improving the water permeability of the semi-permeable membrane while minimizing the decrease in the water permeability of the semi-permeable membrane while obtaining the water quality required for the production water (production water quality). It becomes possible to suppress.

  Specifically, in a situation where the obtained production water quality exceeds the required water quality (water quality reference value), the step A is prescribed to improve the blocking performance of the semipermeable membrane. The condition for prescribing the process A is when the quality of the produced water exceeds or is expected to exceed the reference value.

The prescription can also be determined based on the solute permeability coefficient of the semipermeable membrane or a parameter calculated based on the solute permeability coefficient. The parameters include a predicted value of production water quality, standard performance, and the like.
Furthermore, as a condition that largely affects the permeation performance of the semipermeable membrane, the temperature of the water to be treated can be mentioned.
That is, when the quality of the obtained production water exceeds the reference value, when the solute permeability coefficient of the semipermeable membrane exceeds the reference value, and at least one selected from the case where the temperature of the water to be treated exceeds the reference value. In the case of 1, it is preferable to carry out the step A.

  Of these, the temperature of the water to be treated has the greatest effect on the quality of the produced water and is easy to measure. Therefore, it is also preferable to prescribe the step A based on the water temperature.

That is, in addition to the case where the temperature of the water to be treated has risen above the reference value, the flow rate of the produced water increases due to fluctuations in the properties of the water to be treated, or the operating pressure decreases when the operation is performed at a constant amount of the produced water, and the energy is reduced. When there is a margin, the process A can be prescribed based on the production water flow rate and the operating pressure, or based on the pure water permeability coefficient of the semipermeable membrane and the parameters calculated based on the pure water permeability coefficient. It can also be determined that step A is prescribed. The parameters include a production water flow rate, a predicted value of an operating pressure, a standard performance, and the like.
Such control is suitable when not only the water quality but also the amount of water is important, such as wastewater treatment and landscape water.

The same applies to step B. That is, when the operating pressure is higher than the reference value, when the obtained flow rate of the produced water is lower than the reference value, when the pure water permeability coefficient of the semipermeable membrane is lower than the reference value, and when the temperature of the water to be treated is higher than the reference value. It is preferable to carry out the step B in at least one case selected from cases where the value is below the value.
The case where the operating pressure is higher than the reference value includes a case where the quality of the produced water is lower than the reference value (when the value is within the standard), and the like. The prescription can be determined based on a parameter calculated based on the solute permeability coefficient of the membrane or the solute permeability coefficient of the semipermeable membrane.

  There is no particular limitation on the method of setting conditions for shifting to the step A or the step B, but the step A is a step that contributes to the improvement of the quality of the produced water and the step B is a step that contributes to the improvement of the amount of the produced water (or the operating pressure). Using the quality of production water as an index, prescribe process A when the quality of production water exceeds the reference value, and formulate process B when the amount of production water falls below the reference value (or when the operating pressure exceeds the reference value). Is preferred. However, in the case of emphasis on production water quality, even if the production water flow rate is below the reference value or the operating pressure exceeds the reference value, a decrease in the production water flow rate is acceptable as long as the production water quality does not fall below the reference value. It is preferable to perform control so as not to prescribe the step B within the range. If neither the production water quality nor the production water flow rate can satisfy the standard values, the semipermeable membrane can be washed.However, if the water quality is not improved by washing, the semipermeable membrane can be replaced with a new one. Required.

In addition, due to the characteristics of the semipermeable membrane to which the present invention is applied, the permeation coefficient of the solute tends to increase relatively during the high water temperature period when the temperature of the water to be treated is high, that is, the quality of the produced water tends to deteriorate. On the other hand, in the low water temperature period when the temperature of the water to be treated is low, the water permeability coefficient relatively decreases. Therefore, it is necessary to increase the operating pressure in order to maintain the flow rate of the produced water.
In view of this point, as a result of the study by the present inventors, the process A is performed at a time when the water temperature is expected to rise in the future (a water temperature rising period between the lowest water temperature period and the highest water temperature period), and the process B is performed. However, it is simple and preferable to carry out the process at a time when the water temperature is expected to decrease in the future (the water temperature drop period which is between the highest water temperature period and the lowest water temperature period) under the approximate conditions.

  More specifically, although it differs depending on the climate, for example, in the spring (transition from a low water temperature in winter to a high water temperature in summer), the process A is prescribed in the first week of April, for example, and in autumn (in summer from high water temperature to water temperature). It is preferable to perform an operation of prescribing the process B in the first week of October, for example, as a transition period to the winter season when the temperature is low.

It is also preferable to determine the prescription using a combination of time and temperature. For example, when the temperature of the water simply rises and becomes 20 ° C. or higher during the period from February to August, the process A is performed once, and then, during the period from September to January, the process A is performed. When the temperature becomes lower than or equal to ° C., the process B is performed once.
Such a method is a particularly preferable operation method particularly in the case of a small-scale device or in a case where it is not easy to precisely collect water quality, temperature, and the like.

  As a specific method of the step A, a method of improving the inhibition performance as shown in the background art can be applied. Further, when performing the inhibition performance improving treatment, it is possible to select the type of solute and its concentration depending on the type of the inhibition performance improving agent and the state of the semipermeable membrane as described below.

[Case A: improver L + solute L]
When a rejection performance improving agent having a low rejection in a semipermeable membrane (hereinafter, enhancer L) is used, when a liquid containing a solute having a low rejection performance (hereinafter, solute L) or a liquid having a low osmotic pressure is used, semipermeable membrane is used. Both the concentration of the inhibitor and the osmotic pressure increase due to the concentration caused by the separation of the permeated water from the inlet to the outlet of the membrane unit are unlikely to occur, and the uniform contact of the inhibitor between the inlet and the outlet over the entire semipermeable membrane. Can be obtained. That is, it means that the process of improving the blocking performance of the semipermeable membrane is easily performed uniformly.
Specifically, for example, when the change in the effect of the deterioration of the semipermeable membrane on the semipermeable membrane from the inlet to the outlet is small, such as the temperature of the water to be treated, the combination of the improver L and the solute L is suitable.

[Case B: improver H + solute H]
When a rejection enhancer having a high rejection in a semipermeable membrane (hereinafter, enhancer H) is used, a liquid containing a solute having a high rejection performance (hereinafter, solute H) or a liquid having a high osmotic pressure is used. Concentration caused by separation of permeated water from the inlet to the outlet of the membrane unit increases the concentration of the enhancer H as it goes to the outlet. However, the concentration of solute H also increases. As a result, the permeation flux decreases from the inlet to the outlet. As a result, at the inlet, the concentration of the blocking performance enhancer is low and the permeation flux is large, and at the outlet, the concentration of the blocking performance enhancer is high, and Since the flux is small, the contacting performance-improving agent is preferable because the balance is improved from the entrance to the exit. Further, depending on the operating conditions, it is possible to make the effect onset speed at the entrance relatively slightly higher or relatively lower.
Specifically, similarly to the case A, for example, when the change in the effect of the deterioration of the semipermeable membrane on the semipermeable membrane from the inlet to the outlet is small, such as the temperature of the feed water to be treated, or If there is some change in the effect, a combination of enhancer H + solute H is suitable.

[Case C: improver L + solute H]
In the case of the improver L, if the solute (hereinafter referred to as solute H) which has a sufficiently high blocking performance by the semipermeable membrane and generates osmotic pressure is contained, the permeation flux becomes large near the inlet of the semipermeable membrane unit, and the blocking performance becomes high. The effect developing speed by the improver is large, and the permeation flux decreases due to the increase in osmotic pressure accompanying the solute concentration near the outlet, and the effect developing speed of the inhibitory performance improver decreases. That is, when a large improvement in the blocking performance is required near the entrance, this is a preferred embodiment.
Specifically, for example, as in seawater desalination, near the inlet of the semipermeable membrane unit, the permeation flux in the fresh water is larger than that near the outlet, and the fouling is easy, and the oxidizing agent is also a semipermeable membrane. , The influence of the oxidizing agent is greater near the entrance, and the deterioration of the semipermeable membrane is relatively greater. Therefore, in such a case, a method of actively treating the vicinity of the inlet with a combination of the improver L and the solute H is suitable. In the case of seawater desalination, this method is particularly suitable since seawater can be used as the solute H.

[Case D: improver H + solute L]
In the case of the enhancer H, the concentration is increased as the concentration of the inhibitory performance improver approaches the outlet. On the other hand, since the rise in osmotic pressure due to solute concentration is small, the effect speed of the inhibitory performance enhancer increases from the inlet to the outlet. Such a method is effective when the semipermeable membrane is more damaged near the outlet, for example, when scale deposition occurs.
Further, in the process of improving the inhibition performance, the case is reversed by reversing the supply direction to the semipermeable membrane, for example, by connecting the chemical supply line 14 and the concentrated chemical line 11b as shown in FIG. C and case D are reversed, that is, the improver L + solute H preferentially improves the performance near the outlet at the time of fresh water, or the improver H + solute L preferentially improves the performance near the inlet at the time of fresh water. Can be done. Of course, as illustrated in FIG. 3, it is preferable to be able to switch between the chemical liquid supply line 14 and the concentrated chemical liquid line 11b, and it is possible to intermittently reverse the flow.

Here, as a component contained in the inhibitory performance improver used in the present invention, a vinyl polymer or a compound having a polyalkylene glycol chain is typical, and it is preferable to contain a compound having a polyalkylene glycol chain.
Examples of the vinyl polymer include polyvinyl acetate, polyvinyl alcohol, vinyl acetate-ethylene copolymer, polyethylene alcohol, vinyl acetate-ethylene copolymer, vinyl chloride copolymer, styrene-vinyl acetate copolymer, and N-vinylpyrrolidone. -Vinyl acetate copolymer and the like.
Examples of the polyalkylene glycol chain include a polyethylene glycol chain, a polypropylene glycol chain, a polytrimethylene glycol chain, a polytetramethylene glycol chain, and the like. These glycol chains can be formed by, for example, ring-opening polymerization of ethylene oxide, propylene oxide, oxetane, tetrahydrofuran and the like.

  Furthermore, the inhibitory performance improver applied to the present invention is required to contain other solutes, and as the component, although not particularly limited, an oxidizing agent or the like that affects the performance of the semipermeable membrane. It is necessary to pay attention to the fact that compounds such as turbidity, compounds such as surfactants which adsorb to the membrane and cause deterioration in performance, and components such as organic solvents and oils are not contained. From this viewpoint, it is particularly preferable to apply a compound having a polyalkylene glycol chain to a semipermeable membrane containing polyamide as a main component, since the effect is large.

As the compound having a polyalkylene glycol chain of the present invention, a compound having an ionic group introduced into the polyalkylene glycol chain can be used.
Examples of the ionic group include a sulfo group, a carboxy group, a phospho group, an amino group, and a quaternary ammonium group. By introducing these ionic groups, a water-soluble polymer compound having anionic or cationic properties can be obtained.
The polyalkylene glycol chain in the present invention is particularly preferably a polyethylene glycol chain. The compound having a polyethylene glycol chain has high water solubility and is easy to handle as a rejection improver, and has a high affinity for the surface of the composite membrane.

  Among these, as the improver L and the solute L, those having a blocking performance of the applied semipermeable membrane of 50% or less are preferable, and those having a blocking performance of 20% or less are more preferable. Conversely, as the improver H and the solute H, those having a semipermeable membrane blocking performance of preferably 70% or more, more preferably 90% or more.

  The polymer to which the present invention is applied can be appropriately selected according to the component for which the performance and the blocking performance of the semipermeable membrane are desired to be improved. For example, specifically, in the case of a reverse osmosis membrane having a removal rate of sodium chloride of 90% or more, and in the case of using a polyalkylene glycol as a blocking performance improver, the weight average molecular weight is preferably 6,000 or more and 100,000 or less. And more preferably 7,500 to 50,000. If the weight average molecular weight of the polyalkylene glycol chain is less than 6,000, the rejection of the semipermeable membrane may not be sufficiently improved, and the fixability after the treatment may be low. By controlling the weight average molecular weight to 100,000 or less, it is possible to suppress extremely low permeation flux, maintain good solubility in water, and perform easy handling.

  Further, when it is desired to increase the blocking performance of non-dissociated boron or the like which is very difficult to remove with a semipermeable membrane, a blocking performance improver having a weight average molecular weight of 2,000 or less is preferable, and a polyolefin having a weight average molecular weight of 2,000 or less is preferable. It is more effective to contain an alkylene glycol chain. As a semipermeable membrane suitable for this method, a removal rate of 2,000 mg / L sodium chloride is preferably 99.5% or more, and particularly preferably applied to a high removal rate membrane expressing 99.8% or more. It is.

  On the other hand, in the case of a loose RO membrane (reverse osmosis membrane) or a nanofiltration membrane in which the removal rate of sodium chloride is 50% or less, the weight average molecular weight of the polyalkylene glycol as a rejection enhancer is increased to 10,000 or more. If it is less than 2,000, it is effective. In particular, when a divalent ion is to be removed without removing a monovalent ion such as a loose RO membrane or a nanofiltration membrane, a polyalkylene glycol having a weight average molecular weight of 20,000 or more is used. It is more preferable because the divalent ion removal performance can be improved without increasing the ion blocking performance as much as possible.

  The weight average molecular weight can be determined by analyzing an aqueous solution of a compound having a polyalkylene glycol chain by gel permeation chromatography (GPC) and converting the obtained chromatogram into the molecular weight of a polyethylene oxide standard product.

Furthermore, when a semipermeable membrane for seawater desalination is used, it is preferable to use the inhibitory performance enhancer H as the inhibitory performance enhancer of the present invention, because of the high inhibitory performance of the semipermeable membrane.
In the case of a semipermeable membrane for seawater desalination, the weight average molecular weight is preferably from 2,000 to 50,000, particularly preferably from 2,000 to 20,000. In the case of a low-pressure reverse osmosis membrane, a loose reverse osmosis membrane (RO membrane), or a semipermeable membrane such as a nanofiltration membrane, which has a smaller inhibitory performance than seawater desalination, the weight average molecular weight is 6,000 to 100,000. The following is preferred.

  When a liquid containing an inhibitory performance enhancer is contact-treated with a semipermeable membrane so that the permeation flux is 0.01 to 2.0 m / day, the inhibitory performance enhancer acts even inside the semipermeable membrane. It is easy to do and is preferable. When the permeation flux is 0.01 m / day or less, the treatment effect is low. When the permeation flux is 2.0 m / day or more, the composite semipermeable membrane may be damaged due to excessive operating pressure.

The concentration of the inhibitor is not particularly limited. However, if the concentration is too high, it may be difficult to obtain a uniform improvement of the inhibitor throughout the film, and the inhibitor may be accumulated locally. Therefore, a local decrease in water permeability may occur. On the other hand, if the concentration is too low, the speed of improvement of the blocking performance is reduced, and the processing time may be increased.
Specifically, it is preferably from 0.5 μmol / L to 100 μmol / L, and more preferably from 1 μmol / L to 50 μmol / L.

  Furthermore, the concentration can be gradually increased and decreased while monitoring the permeation flux during the inhibition performance improving process in order to enhance the effect and time efficiency of the process. By measuring the permeation flux during processing, when the concentration is too low and the effect of improving the rejection is not obtained or when the effect per time is too large and it is judged that uniform processing is difficult to perform, It is possible to immediately increase or decrease the treatment concentration, which is particularly effective when treating on a large scale such as a water treatment plant.

  In addition, by heating and supplying the liquid containing the inhibitory performance improving agent, the speed of diffusion and contact with the semipermeable membrane can be increased, which is preferable. Specifically, it is the operating temperature at the time of fresh water production of the semipermeable membrane, and is preferably not less than the highest temperature at the time of fresh water production and 60 ° C or less, from the viewpoint of preventing deterioration of the semipermeable membrane due to heat, more preferably, The temperature is 35 ° C or more and 45 ° C or less.

In the present invention, it is also preferable to adopt a method in which high-temperature water is brought into contact with the blocking performance improving agent so that the blocking performance improving agent is hardly desorbed from the semipermeable membrane. As a specific method, it is possible to increase the ambient temperature.However, after the inhibition performance improving treatment, supply water, concentrated water, permeated water, and other water outside the system during fresh water production during fresh water production operation By passing water through the supply side of the semipermeable membrane at a temperature equal to or higher than the maximum temperature.
The specific temperature is preferably not lower than the maximum temperature during the fresh water driving operation and not higher than 60 ° C. from the viewpoint of preventing deterioration of the semipermeable membrane, and more preferably not lower than 35 ° C. and not higher than 45 ° C.

  The conditions such as the flow rate and the pH at this time are not particularly limited, but a mild flow rate and pH that do not adversely affect the semipermeable membrane and the result of the treatment for improving the inhibition performance are preferable. Also, the pressure at this time is preferably equal to or lower than the operating pressure at the time of fresh water generation. As the warm water at this time, it is possible to heat a liquid containing an inhibitory performance improving agent (inhibiting performance improving liquid) and pass the water as it is, but since the heating has an effect of accelerating the process, the process is terminated. Attention must be paid to the fact that the prevention performance improvement processing must be completed earlier than in the case where heating is performed and heating is not performed and heating is not performed.

  As a method of enhancing the effect of the blocking performance treatment in the present invention, it is also effective to temporarily change the pressure on the liquid side to be treated during treatment, that is, on the primary side. Specifically, it is preferable to change the pressure during the treatment at a rate of change of 0.05 MPa / s or more for 10 seconds or more. In addition, the number of times is not limited, and it is preferable to carry out the operation intermittently while monitoring the effect.

A similar effect can be obtained by changing the permeation flow rate. In this case, as described above, this can be achieved by a change in the pressure on the primary side, but can also be achieved by a change in the pressure on the secondary side.
Further, the permeation flux can be changed by changing the osmotic pressure on the membrane surface by changing the concentration of the solute shown in the present invention. In such a case, when the raw water at the time of fresh water generation is seawater, it is preferable because the osmotic pressure can be largely changed without increasing the chemical cost. Here, it is effective to change the permeation flux by 0.8 times or less or 1.2 times or more before the change, but a rapid change imposes a load on the semipermeable membrane. Therefore, it is more preferable that the ratio be 0.6 times or more and 0.8 times or less, or 1.2 times or more and 1.5 times or less.

  The time for passing the liquid containing the inhibitory performance improver can be appropriately determined according to the present invention, but is preferably 0.5 to 24 hours, more preferably 1 to 12 hours. As described above, if the processing time is too short, uniform processing may be difficult, and if the processing time is too long, the operating time of the equipment may be lost.

  In the case of performing the inhibition performance improving process (Step A), a more persistent recovery effect can be obtained by removing the membrane contaminants on the semipermeable membrane surface before the contact process. That is, it is preferable to wash the semipermeable membrane before performing the step A.

As a method for removing film contaminants, chemicals generally used as cleaning chemicals for these films can be used. Metals such as iron and manganese adhering to the film surface are preferably washed with an acidic solution such as citric acid, oxalic acid, hydrochloric acid, or sulfuric acid because they are more effective, and the cleaning effect is obtained by using a pH of 3 or less. Can be further enhanced.
When organic substances and microorganisms are attached to the membrane surface, washing with an alkaline solution such as caustic soda or tetrasodium ethylenediaminetetraacetate is effective, and the washing effect can be enhanced by using a pH of 10 or more. .
The cleaning with these cleaning chemicals may be a method of cleaning individually using each chemical or a method of cleaning using a plurality of chemicals alternately. Further, it is also possible to mix the cleaning chemical with the inhibiting performance improving agent and carry out the cleaning and the step A at the same time.

  When the liquid containing the inhibitory performance enhancer of the present invention is supplied under pressure, if a liquid to which the inhibitory performance enhancer and a solute are added in advance can be prepared in the chemical solution tank 15, for example, as shown in FIG. It is also possible to add the inhibitory performance improving agent by the addition unit 20a and add the solute by the chemical solution addition unit 20b.

Furthermore, it is also preferable to apply a solute containing semi-permeable membrane feed water or semi-permeable membrane concentrated water as the solute of the present invention.
In this case, for example, first, any one of the semipermeable membrane supply water, the semipermeable membrane concentrated water, and the semipermeable membrane permeated water is supplied and stored in the chemical solution tank 15 during the fresh water producing operation or before and after the fresh water producing operation. At the same time or after the storage operation is completed, the inhibitory performance improving agent is added from the chemical solution adding unit 20a so as to have a predetermined concentration. Accordingly, it is not necessary to procure the solute / solvent for the liquid of the present invention from outside the system, and it is possible to prepare a liquid having an osmotic pressure according to the purpose. Further, the solute may be supplied from outside the system, that is, by the chemical solution adding unit 20b, using the semipermeable membrane permeated water as a solvent.

  Above all, in the fresh water operating conditions, the liquid containing the inhibitory performance enhancer is used as the liquid to which the inhibitory performance enhancer is added to the water to be treated, and the process A is performed while obtaining the production water. It is particularly efficient to carry out the water production and the inhibition performance improvement treatment (step A) simultaneously while adding the performance improver. That is, by pre-treating the raw water to be treated and adding an inhibitory performance-improving agent to the pre-treated water, the treatment and fresh water can be performed simultaneously.

  In particular, in the case of this method, since the operation is performed while the fresh water is being produced, the fresh water producing pressure, the fresh water quantity, and the quality of the permeated water can be monitored in real time, which is very preferable from the viewpoint of control. That is, for example, when the permeated water quality, rejection rate, and / or solute permeation coefficient are worse than the set concentration, a method of adding a rejection performance improver and stopping the addition when the rejection performance falls within an allowable value is adopted. It is very preferable because it can be used. However, in this case, in the unlikely event that there is a risk that the inhibiting performance improver is mixed into the produced water. Therefore, a process to further treat the permeated water is provided to prevent the blocking performance improver from mixing into the production water, use a blocking performance improver that has been confirmed to be safe for the application, or improve the blocking performance in the permeated water. It is necessary to strictly monitor the concentration of the agent and immediately stop water production.

In the step B, the semipermeable membrane may be washed before the step B. However, if the membrane contaminants on the semipermeable membrane surface are removed in advance, the step B can be performed more effectively. There is.
Further, it is more preferable to remove the contaminants at the same time as removing the inhibitory performance enhancer attached to the membrane surface of the semipermeable membrane in step B. That is, it is more preferable to perform the cleaning of the semipermeable membrane simultaneously with the step B.

When the semi-permeable membrane is washed before or at the same time as the step B, when the inhibitory performance improver used in the step A contains a compound having a polyalkylene glycol chain, (i) a surfactant or , (Ii) a remover containing a compound having at least one selected from a pyridine ring, an alkylamine chain and a piperidine ring. Further, it is preferable that the liquid containing the (iii) removing agent is alkaline, since the removing effect is high. That is, it is preferable that at least one of the above (i) to (iii) is satisfied.
Above all, in the case of the above (iii), if the removing agent is a highly alkaline liquid, the alkali cleaning of the semipermeable membrane and the step B can be performed simultaneously, which is a very preferable embodiment.

  Further, since the step B is intended to remove and remove the inhibitory performance improving agent attached to the water-to-be-treated side of the semipermeable membrane, the process B is carried out from the permeated-water side of the semipermeable membrane unit during the step B. It is effective to allow water or solution to permeate the water side. As this method, besides a method of applying pressure from the permeated water side to the treated water side, a method of contacting water having a lower osmotic pressure than the remover-containing liquid on the treated water side, and permeating water by forward osmosis. It can also be preferred.

As the material of the semipermeable membrane applicable to the present invention, a polymer material such as a cellulose acetate polymer, polyamide, polyester, polyimide, and vinyl polymer can be used. In addition, the membrane structure has a dense layer on at least one side of the membrane, and an asymmetric membrane having fine pores having a large pore diameter gradually from the dense layer toward the inside of the membrane or the other side, or another material on the support membrane. A composite semipermeable membrane having a very thin separation function layer formed by the method described above can be used.
In particular, the semipermeable membrane suitable for the present invention has both high pressure resistance and high water permeability, high solute removal performance, and has excellent performance. preferable.

In the case where seawater is used as the water to be treated, it is necessary to apply a pressure higher than the osmotic pressure to the composite semipermeable membrane, and an operating pressure of at least 5 MPa is often applied substantially. In order to maintain high water permeability and blocking performance against this pressure, a structure in which polyamide is used as a separation function layer and held by a support made of a microporous membrane or a nonwoven fabric is suitable.
However, in the case of a composite membrane, as described above, in step B, when the flow rate or pressure flowing when permeating water or the like from the permeated water side to the treated water side is excessively large, the functional layer is peeled off, and the membrane is damaged. May cause Therefore, it is important to appropriately control the flow rate and pressure from the permeated water side to prevent separation of the composite membrane.

  As the polyamide semipermeable membrane, a composite semipermeable membrane having a separation functional layer of a crosslinked polyamide obtained by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide is preferable. Further, the composite semipermeable membrane is preferable from the viewpoint that the amount of the separation function layer is small, so that the blocking performance improving agent effectively acts on the functional layer portion exhibiting the blocking performance.

  In such a semi-permeable membrane for water treatment, the pH of general raw water to be treated is in a neutral region, and in this region, the surface of the membrane is negatively charged to prevent adsorption of natural organic substances. That is, since the film surface potential is negative, the isoelectric point, that is, the surface potential of the film generally becomes 0 in a weakly acidic region.

  When a non-chargeable or weakly-charged inhibitory agent is used in the treatment for improving the inhibition performance according to the present invention, the continuity of the treatment effect can be enhanced by making the surface potential of the semipermeable membrane neutral. Therefore, the treatment is preferably performed in a weakly acidic region, specifically, pH 4 or more and pH 7 or less, more preferably pH 5.5 or more and pH 6.8 or less.

In the present invention, the semipermeable membrane can be used as a semipermeable membrane element configured for practical use. When the membrane form of the semipermeable membrane is a flat membrane, it can be used by incorporating it into a spiral, tubular, plate and frame module. In the case of using a spiral shape, on the structure, the rejection performance improver flows in one direction from one end face to the other end face, and a member such as a feed water side flow path material and a permeate flow side flow path material is incorporated. Therefore, the blocking performance improver easily acts uniformly on the membrane surface, and is particularly preferably used as a semipermeable membrane element to which the present invention is applied.
Among them, the supply water side channel material through which the liquid containing the blocking performance improver is passed, the thickness is preferably 0.6 mm or more and 1.0 mm or less, particularly preferably 0.7 m or more and 0.9 mm or less. . In addition, it is preferable to apply to a spiral element having a porosity of 0.8 or more, because the treatment liquids can be easily uniformly contacted.

  In the method for improving the blocking performance of the present invention (Step A), the rejection of the semipermeable membrane is improved by bringing the liquid containing the blocking performance improver into contact with the semipermeable membrane, but the permeation flux decreases accordingly. . Therefore, it is very important to monitor and control the water permeation performance and the blocking performance before and after the blocking performance treatment in order to prevent the excessive increase in operating pressure due to the reduced water permeability while making full use of the improvement effect of the blocking performance. It is.

Specifically, at least before the inhibition performance improvement treatment, components other than those containing no inhibition performance improvement treatment agent are passed through the reverse osmosis membrane using the same liquid, and the supply water, permeate water, and concentrated water at that time Among them, at least two flow rates, concentrations, and water temperatures are measured, and a pure water permeability coefficient A ₀ as the initial water permeability and a solute permeability coefficient B ₀ as the rejection performance are calculated therefrom. Then, while supplying and passing the reverse osmosis membrane with the treatment liquid for improving the inhibition performance, at least two flow rates, concentrations, and water temperatures of the supply water, permeate water, and concentrated water at that time are measured, and the initial permeation performance is determined from them. The pure water permeability coefficient A ₁ and the solute permeability coefficient B ₂ as the inhibition performance are calculated. _Then, the value of _B 1 / _{B 0} when the value of A 1 / _{A 0} is equal to or less than _{R A1} is equal to or less the predetermined value _{R B,} to exit the rejection enhancing _{treatment, B} 1 / If the value of B ₀ exceeds the _{R B,} the value of _B 1 / _{B 0} continues to rejection enhancing treatment is put in the following _{R B,} the value of a 1 / _{a 0} is decreased to _{R A2} At this point, it is preferable to take a method of stopping the inhibition performance improvement processing. Incidentally, more specifically, the _{R A1} is 0.9 or less, _and, together with _{R A2} is so is 0.7 or more, rejection performance as _{R B} is 0.3 to 0.7 It is more preferable to perform an improvement process.

The pure water permeability coefficient A and the solute permeability coefficient B in the present invention can be determined by the following method.
Jv = A (ΔP−π (Cm)) (1)
Js = B (Cm-Cp) (2)
(Cm-Cp) / (Cf-Cp) = exp (Jv / k) (3)
Cp = Js / Jv (4)
A = α × A25 × μ25 / μ (5)
B = β × B25 × μ25 / μ × (273.15 + T) / (298.15) (6)
Cf: Supply water concentration [mg / l]
Cm: film surface concentration [mg / l]
Cp: permeate concentration [mg / l]
Js: solute flux [kg / m ² / s]
Jv: Pure water permeation flux [m ³ / m ² / s]
k: Mass transfer coefficient [m / s]
A: Pure water permeability coefficient [m ³ / m ² / Pa / s]
A25: Pure water permeability coefficient at 25 ° C. [m ³ / m ² / Pa / s]
B: solute permeability coefficient [m / s]
B25: solute permeability coefficient at 25 ° C. [m ³ / m ² / Pa / s]
T: Temperature [° C]
α: Coefficient of variation depending on operating conditions [-]
β: Coefficient of variation depending on operating conditions [-]
ΔP: Operating pressure [Pa]
μ: viscosity [Pa · s]
μ25: viscosity at 25 ° C. [Pa · s]
π: Osmotic pressure [Pa]

That is, the values of Jv, Cf, Cp and T are actually measured, and k and other physical properties are substituted into the above equations (1) to (4) to obtain the pure water permeability coefficient A and the solute permeability coefficient B under the actual measurement conditions. Can be requested.
Further, based on the previously obtained values of the coefficients α and β, the pure water permeability coefficient A25 and the solute permeability coefficient B25 at 25 ° C. can be obtained from the equations (5) and (6), respectively. , Equations (5) and (6) can be used to obtain the pure water permeability coefficient and solute permeability coefficient at an arbitrary temperature T.
When calculating the performance of the semipermeable membrane element, the performance can be obtained by numerical integration while calculating the material balance in the length direction of the semipermeable membrane element.

  The details of this calculation method are described in Non-Patent Document (M. Taniguchi et al., Behavior of a reverse osmos plant planting a brine conversion, Journal of Membrane Science, 183, pp. 249-257 (2000)).

In calculating and monitoring the pure water permeability coefficient A and the solute permeability coefficient B, it is preferable that both values are corrected to the same temperature, but the water permeability is the strictest, that is, the pure water permeability coefficient A is the lowest. the most stringent for the lowest operating temperature T _L, and rejection performance of the semipermeable membrane, i.e. the solute permeability coefficient B is corrected to a value at the maximum operating temperature T _H of the largest becomes a semi-permeable membrane, or the performance of each is within the allowable range It is very preferable because it is easy to understand.

  In the present invention, for carrying out the step A, for example, a method in which a liquid containing an inhibitory performance improving agent is passed through a pressure vessel while the semipermeable membrane is loaded in the pressure vessel, and the semipermeable membrane is brought into contact with the semipermeable membrane to perform the treatment. Can be If there is equipment for chemical cleaning with the semi-permeable membrane loaded in the pressure vessel, use the washing equipment to pass the liquid containing the inhibitory performance improver through the pressure vessel and contact the semi-permeable membrane for treatment. can do.

  The pressure at which the aqueous solution containing the inhibitory performance enhancer is contacted with the composite semipermeable membrane is not particularly limited, and may be appropriately determined in consideration of the pressure resistance of the semipermeable membrane, the effect of improving the inhibitory performance, and the effect on the water permeability. Can be. Among them, it is preferable that the pressure is lower than the pressure at which the water to be treated is passed through the semipermeable membrane and the water is desirably operated. This is more preferable because the inhibition performance can be improved without providing special equipment.

  When the liquid containing an inhibitory performance improver is contact-adhered to the semi-permeable membrane, the flux is preferably adjusted to 0.01 to 2.0 m / day so that the inhibitory improver reaches the inside of the semi-permeable membrane. It is preferable because it works easily. When the permeation flux is 0.01 m / day or less, the treatment effect is low. When the permeation flux is 2.0 m / day or more, the composite semipermeable membrane may be damaged by excessive operating pressure.

  In addition, the method for improving rejection performance (step A) of the present invention can improve the rejection with a repetitive effect on the same semipermeable membrane in the same water treatment facility. By carrying out, a constant removal rate can be maintained for a long time. In particular, the effect of improving the uncharged substance removal rate is greater than that of an inorganic electrolyte which has an effect of being eliminated by charging the membrane. Examples of the non-charged substance include a non-electrolyte organic substance and a substance (for example, boron or silica) that is not separated in a neutral region. Since these are contained in a large amount in seawater and groundwater, more stable operation can be continued by applying the method of the present invention to a desalination plant for treating such raw water.

Hereinafter, the present invention will be described in more detail with reference to Examples. Note that the present invention is not limited by these examples.
<Performance evaluation>
<New membrane performance>
FIG. An evaluation device using the same flat membrane evaluation cell as in Example 1 as a semipermeable membrane unit was used. FIG. 4 shows the flow.
The apparatus shown in FIG. 4 includes a UF filtration module filled with activated carbon, a UF filtration module filled with activated carbon, a pretreatment water supply pump 6, a security filter 7, a booster pump 8, a semi-permeable water tank 2, a treatment water supply pump 3, and a pretreatment unit 4. It comprises a membrane unit 9, a concentrated water valve 18, and a temperature control unit 21. The water to be treated is maintained as clear, temperature-controlled water by circulating through the pretreatment unit 4 and the temperature control unit 21.
Using this apparatus, a Toray aromatic polyamide reverse osmosis membrane, an aqueous solution of 32,000 [mg / L-NaCl], 25 ° C., pH = 7 was used as the evaluation supply water (treatment water), and the operating pressure was 5. The permeation flux was 0.98 [m / day] and the concentration of NaCl in the permeated water was 60 mg / L when circulating and pressurized at 5 [MPa] at a supply flow rate of 3.5 [L / min]. Thereafter, the feed water temperature was raised to 40 ° C., and the operating pressure was adjusted so that the permeation flux was the same. As a result, the operation pressure was 4.85 MPa, the permeate NaCl concentration was 85 mg / L, and in the state of a new membrane, It was below 100 mg / L. Subsequently, when the supply water temperature was lowered to 10 ° C., the operating pressure rose to 6.86 MPa, and the permeate quality became 40 mg / L.

<Degraded film performance>
The same membrane as that used in the above <New membrane performance> is immersed in a 100 mg / L aqueous solution of hypochlorous acid for 2 hours to chemically deteriorate the membrane, and then the evaluation supply water is supplied to the membrane at 45 ° C. and 7 MPa. A physically degraded film was produced. The operating pressure of this membrane was adjusted again under the same conditions of 40 ° C. so that the permeation flux became the same. As a result, the operating pressure was 5.16 MPa, and the NaCl concentration of the permeated water at that time was 150 mg / L, and 100 mg / L. Exceeded. Conversely, when the water temperature was lowered to 10 ° C., the operating pressure was 6.23 MPa, and the permeate quality was 70 mg / L.

<Improved processing film performance>
For the deteriorated film used in the above <Degraded film performance>, using the same flat film evaluation device, a liquid obtained by adding 2 μmol / L of polyethylene glycol having a weight average molecular weight of 8,000 to pure water as a rejection performance improver was used. The solution was circulated at 3.5 L, 25 ° C. and a pressure of 0.45 MPa. At this time, the permeated water and the concentrated water were all circulated. The average flux during the treatment was 0.16 m / day. Subsequently, after the treatment, an aqueous solution of 32,000 [mg / l-NaCl], 25 ° C. and pH = 7 was again supplied at the same supply flux at a supply flow rate of 3.5 [L / min] and a standard condition of 25 ° C. As a result, the operating pressure was 6.4 MPa, the permeate quality was 70 mg / L, the operating pressure was 7 MPa or less, and the permeate quality was 100 mg / L or less. Subsequently, when the temperature was raised to 40 ° C., the operating pressure was 5.8 MPa, the permeated water quality was 98 mg / L, and the water quality was improved to 100 mg / L or less by the inhibition performance improving treatment. However, when the water temperature was lowered to 10 ° C., the permeated water quality was sufficiently good at 45 mg / L, but the operating pressure increased to 7.5 MPa and exceeded 7 MPa.

<Release treatment film performance>
The membrane used in the above <Improved treatment membrane performance> was circulated with a NaOH aqueous solution having a pH of 12 at a flow rate of 3.5 L at 25 ° C. and a pressure of 0.05 MPa using the same flat membrane evaluation device, and an inhibitory agent for inhibiting performance was obtained. Removal processing was performed. At this time, the permeated water and the concentrated water were all circulated. Subsequently, after the treatment, an aqueous solution of 32,000 [mg / l-NaCl], 25 ° C., pH = 7 was again supplied under the conditions of a supply flow rate of 3.5 [L / min] and 25 ° C., at the same permeation flux. As a result, the operating pressure was 5.7 MPa, the permeate quality was 94 mg / L, the operation pressure was 7 MPa or less, and the permeate quality was 100 mg / L or less. Subsequently, when the water temperature was raised to 40 ° C., the operating pressure was 5.3 MPa, the permeated water quality was 140 mg / L, and the water quality was deteriorated beyond 100 mg / L by the removal treatment. However, when the water temperature was lowered to 10 ° C., the permeated water quality was sufficiently good at 63 mg / L, and the operating pressure was 6.3 MPa, which was much lower than 7 MPa.

<Example 1>
From the above performance evaluation results, in the situation where the membrane is deteriorated, if the one-year water temperature fluctuation is assumed to be 10 ° C. to 40 ° C., it is prevented from 25 ° C. or less to exceeding 25 ° C., that is, from winter to spring to summer. When the performance improvement treatment is performed, and conversely, when the blocking performance improver is removed from 25 ° C. or higher to lower than 25 ° C., that is, from summer to autumn to winter, the maximum pressure in winter (10 ° C.) is 6.3 MPa, in the summer (40 ° C.), the maximum permeated water quality was 95 mg / L, suggesting that 100 mg / L can always be maintained with an equipment capacity of an operating pressure of 7 MPa or less.

<Comparative Example 1>
Similarly, from the performance evaluation results, it was suggested that the permeated water quality of the deteriorated membrane was 150 mg / L in the high temperature period (summer season), and it was not possible to satisfy 100 mg / L or less.
<Comparative Example 2>
Furthermore, in the case of the membrane treated to improve the inhibition performance, the operating pressure increased to 7.5 MPa in the low temperature period (winter period), suggesting that it could not be operated with equipment having a small pressure capacity of 7 MPa.

  Table 1 summarizes the above examples and comparative examples.

  Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application (No. 2015-89987) filed on April 27, 2015, the contents of which are incorporated herein by reference.

  The present invention relates to a semi-permeable membrane separation device using a semi-permeable membrane such as a nanofiltration membrane or a reverse osmosis membrane. This is a method of operating a semipermeable membrane separation apparatus that efficiently uses an improvement process and a washing process for recovering performance deterioration due to fouling, thereby making it possible to produce fresh water while achieving both energy saving and stable production water quality. It becomes possible.

1: treated water line 2: treated water tank 3: treated water supply pump 4: pretreatment unit 5: intermediate water tank 6: pretreated water supply pump 7: security filter 8: booster pump 9: semi-permeable membrane unit 10: Permeate line 11: Concentrate line 12: Production water tank 13: Energy recovery unit 14: Chemical supply line 15: Chemical tank 16 a: Supply water valve 16 b: Supply chemical valve 17 a: Permeate valve 17 b: Permeate chemical valve 18: Concentration Water valve 18a: Concentrated water valve 18b: Concentrated chemical liquid valve 19: Chemical liquid supply pumps 20a, 20b: Chemical liquid addition unit 21: Temperature control unit

Claims (8)

A method for operating a semipermeable membrane separation apparatus, which supplies treated water to a semipermeable membrane unit and obtains product water separated and treated on a permeated water side,
By pressurizing and supplying a liquid containing an inhibitory performance enhancer to the treated water side of the semipermeable membrane unit, by contacting and attaching the inhibitory performance enhancer to the membrane surface of the semipermeable membrane in the semipermeable membrane unit. A step A of improving the blocking performance of the semipermeable membrane; and removing and removing the blocking performance improver attached to the semipermeable membrane with a liquid containing a removing agent, thereby improving the water permeability of the semipermeable membrane. Step B for improvement
Is carried out intermittently ,
In the step A, the inhibitory performance improving agent contains a compound having a polyalkylene glycol chain, and in the step B, (i) the removing agent is a surfactant, and (ii) the removing agent is a pyridine ring. And at least one selected from the group consisting of: a compound having at least one selected from an alkylamine chain and a piperidine ring; and (iii) the liquid containing the removing agent is alkaline.
The step A is performed during a water temperature rising period in which the temperature of the water to be treated is between the minimum water temperature period and the maximum water temperature period, and the step B is performed when the temperature of the water to be treated is from the maximum water temperature period to the minimum water temperature period. A method for operating a semi-permeable membrane separation apparatus, wherein a production water is obtained while performing during a period of falling water temperature . When the quality of the obtained production water exceeds a reference value, when the solute permeability coefficient of the semipermeable membrane exceeds a reference value, and at least one selected from the case where the temperature of the water to be treated exceeds a reference value. In the case where the step A is performed,
If the operating pressure is higher than the reference value, if the obtained flow rate of the produced water is lower than the reference value, if the pure water permeability coefficient of the semipermeable membrane is lower than the reference value, and if the temperature of the water to be treated is lower than the reference value. The method for operating a semipermeable membrane separation device according to claim 1, wherein the step B is performed in at least one case selected from cases in which the ratio is lower than the range.   The method for operating a semipermeable membrane separation device according to claim 1 or 2, wherein the semipermeable membrane is washed before performing at least one of the step A and the step B.   The method for operating a semipermeable membrane separation device according to claim 1 or 2, wherein the semipermeable membrane is washed at the same time as at least one of the step A and the step B is performed.   The method for operating a semipermeable membrane separation apparatus according to claim 4, wherein the semipermeable membrane is washed at the same time as the step B is performed. The method according to any one of claims 1 to 5 , wherein, as the liquid containing the inhibitory performance improver in the step A, a liquid obtained by adding the inhibitory performance enhancer to the water to be treated is used, and the step A is performed while obtaining product water. The method for operating the semipermeable membrane separation device according to claim 1. The operation of the semipermeable membrane separation apparatus according to any one of claims 1 to 6 , wherein water is permeated from the permeated water side of the semipermeable membrane unit to the treated water side during the execution of the step B. Method. The method for operating a semipermeable membrane separation device according to claim 7 , wherein the permeation of water from the permeated water side to the treated water side is by forward osmosis.

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