JP5177538B2 - Pure water production method and pure water production system - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a pure water production method and a pure water production system, and more specifically, a pure water production method for producing high-purity pure water by treating water to be treated with a reverse osmosis membrane, and the production method. The present invention relates to a pure water production system.

  High-purity pure water that does not contain impurities is used in semiconductor manufacturing processes, electronic component cleaning, medical device cleaning, and the like.

  Conventionally, this type of pure water is produced by treating raw water such as groundwater or tap water with a reverse osmosis membrane (hereinafter referred to as “RO membrane”).

  For example, in Patent Document 1, raw water containing a hardness component is treated with a synthetic polymer-based composite membrane module after adding a chelating agent to the raw water in the presence of an oxidizing agent and then treating the raw water with a membrane module. A method has been proposed.

  In Patent Document 1, by injecting a chemical (oxidant) such as sodium hypochlorite into raw water as a bactericidal agent, fouling is prevented from occurring in the filtration membrane, and a chelating agent is added to the raw water. Thus, even when the hardness of the raw water is high, it is possible to prevent the filtration membrane from being oxidized and deteriorated by the catalytic action of the hardness component. That is, according to Patent Document 1, even if an oxidizing agent such as sodium hypochlorite is added, it is possible to suppress the promotion of oxidative degradation of the RO membrane due to the raw water hardness.

  Patent Document 2 discloses a membrane module in which the hardness component of raw water is reduced to 10 ppm or less using a water softener and the raw water is treated with a synthetic polymer composite membrane module in the presence of an oxidizing agent. A method for treating raw water by means of is proposed.

  In Patent Document 2, since membrane filtration treatment is performed on soft water into which a chemical agent to which an oxidizing agent has been added has been injected, the promotion of oxidative degradation of the RO membrane due to the raw water hardness can be suppressed, and it can be attributed to microorganisms. Biofouling can be prevented.

  Further, Patent Document 3 proposes a water treatment method in which water to be treated is treated with soft water, filtered through a reverse osmosis membrane portion, and concentrated drainage generated by the reverse osmosis membrane portion is blown at predetermined intervals. ing.

In Patent Document 3, by treating the water to be treated with soft water, hardness components such as calcium in the water to be treated are removed, so that precipitation of scale due to the bond between the hardness component and silica (SiO ₂ ) is prevented. . Therefore, the silica solubility of the water to be treated is increased, and accordingly, the silica scale deposition is suppressed even when the silica concentration of the water to be treated is high, so that the water treatment operation can be performed even if the silica concentration of the water to be treated is high. It becomes.

  Moreover, since the concentrated water obtained by membrane filtration separation is blown at predetermined intervals, an increase in the silica concentration of the water to be treated in the vicinity of the reverse osmosis membrane portion can be suppressed. In other words, since the precipitation of silica scale is suppressed, clogging of the reverse osmosis membrane portion can be prevented, and as a result, stable water treatment operation can be continuously performed for a long period of time. It is possible to improve the water recovery rate.

Japanese Patent Laid-Open No. 9-891 JP-A-6-226253 JP-A-2005-279460

  However, in Patent Document 1, since the oxidative degradation of the RO membrane is suppressed by adding the chelating agent to the raw water, the chelating agent injecting device becomes empty, or the infusion pump has an abnormality or the like, resulting in poor injection. Or, when the injection becomes impossible, the oxidation deterioration of the RO membrane cannot be suppressed, and the oxidation deterioration may be promoted on the contrary.

  Moreover, in patent document 2, although the soft water whose hardness is 10 ppm or less is used, since oxidizing agent is inject | poured into raw | natural water, there exists a possibility that an RO film may oxidize and deteriorate by continuous operation for a long time.

  Furthermore, as a result of the study by the present inventors, it has been found that when the raw water contains an oxidizing agent such as free chlorine, the silica removal rate by the RO membrane decreases substantially in proportion to the water passage time. Therefore, in Patent Document 2, since raw water containing an oxidant is supplied to the RO device, the silica removal rate by the RO membrane decreases substantially in proportion to the water flow time, and is therefore arranged downstream of the RO membrane. In addition, the load on various devices may increase.

  Moreover, in patent document 3, it is going to suppress the precipitation of the silica scale to RO membrane by using soft water, and it is unclear how hard soft water is used, and how much. It is also unclear whether the product water of the purity is obtained.

  Moreover, when the raw water contains an oxidizing agent such as free chlorine, as in Patent Document 2, the oxidative deterioration of the RO membrane proceeds due to continuous operation for a long time, resulting in a decrease in the silica removal rate. There is a risk of increasing the load on various devices arranged downstream of the RO membrane.

  The present invention has been made in view of such circumstances, and can stably supply high-purity production water while suppressing oxidative deterioration of the RO membrane, and can quickly respond even when oxidative deterioration occurs. An object of the present invention is to provide a pure water production method that can contribute to energy saving and a pure water production system that can be used in this production method.

  A method for treating raw water obtained by softening raw water with an RO membrane has been conventionally known as shown in Patent Document 3 above.

  However, as described in the section [Problems to be solved by the invention], the conventional use of soft water as the water to be treated is mainly intended to prevent scale deposition on the RO membrane. There is no such thing as intended to improve the purity of pure water.

  On the other hand, pure water with as high purity as possible is required in silicon wafer cleaning and pharmaceutical manufacturing processes in semiconductor manufacturing processes such as LSI.

Therefore, the present inventors conducted extensive research using soft water to increase the removal rate of impurities by the RO membrane and obtain pure water with higher purity. As a result, the soft water having a hardness of 5 mg CaCO ₃ / L or less. As a result, it was found that the removal rate of impurities can be further increased by supplying the RO membrane to the RO membrane, thereby stably supplying high-purity pure water. In addition, by using the soft water, the knowledge that the progress of oxidative deterioration can be suppressed if the content of free chlorine in the soft water is minute is also obtained.

Further, as described above, as a result of further diligent research by the present inventors, when an oxidizing agent such as free chlorine is contained in the water to be treated, the electrical conductivity and the removal rate of various ions are continuous for a long time. It has been found that the removal rate of silica decreases remarkably with time from the initial stage of water flow in proportion to the time of water flow, although it hardly varies even when water is passed through. Therefore, by constantly monitoring the silica removal rate, it becomes possible to quickly cope with oxidative degradation of the RO membrane due to free chlorine.

The present invention has been made on the basis of such knowledge, and the method for producing pure water according to the present invention is a method for producing pure water in which treated water is treated with a reverse osmosis membrane to produce product water. The hardness is 5mgCaCO ₃ The raw water is softened so as to be less than / L to produce treated water, and the treated water is treated with the reverse osmosis membrane while monitoring the silica removal rate of the produced water relative to the treated water to produce the produced water. It is characterized by producing water.

As described above, if the content of free chlorine is very small, the hardness is 5 mg CaCO ₃ / L or less, it is possible to suppress the progress of oxidative degradation by using water to be treated, but usually raw water often contains a considerable amount of free chlorine. It is preferable to remove the free chlorine.

Therefore, the method for producing pure water according to the present invention is characterized in that the softening is performed after removing free chlorine contained in the raw water.

Further, the pure water production method of the present invention is characterized in that the RO membrane is an ultra-low pressure membrane that performs membrane filtration separation treatment at an operating pressure of 0.5 MPa or less .

Further, in the method for producing pure water of the present invention, the RO membrane performs an ultra-low pressure membrane that performs a membrane filtration separation process at an operating pressure of 0.5 MPa or less, and a membrane filtration separation process at an operation pressure of 0.7 MPa or less. Including at least two kinds of ultra-low pressure membranes to be treated, wherein the treated water is treated with the ultra-low pressure membrane and then treated with the ultra-low pressure membrane to produce the produced water .

Furthermore, the method for producing pure water according to the present invention is characterized in that the product water has an electrical conductivity removal rate of 98.5% or more with respect to the water to be treated .

In addition, the pure water production system according to the present invention includes a water softener that softens raw water to generate water to be treated, and an RO device that generates product water by processing the water to be treated generated by the water softener ( In a pure water production system equipped with a reverse osmosis membrane filtration device), a silica removal rate monitoring means for monitoring a silica removal rate of the production water relative to the raw water is provided, and the soft water device is 5 mgCaCO ₃ / L or less. It is characterized by having a water to be treated generating means for softening raw water to generate water to be treated.

  The pure water production system of the present invention is characterized by comprising free chlorine removing means for removing free chlorine contained in the raw water.

  In the pure water production system of the present invention, the free chlorine removing means is an activated carbon filtration device.

Moreover, the pure water production system of the present invention is characterized in that the RO device has an ultra-low pressure membrane module including an ultra-low pressure membrane that performs membrane filtration separation processing at an operating pressure of 0.5 MPa or less. It is said.

Furthermore, in the pure water production system of the present invention, the RO device includes two or more types of RO devices including a first RO device and a second RO device, and the first RO device has a pressure of 0.5 MPa. An ultra-low pressure membrane module having an ultra-low pressure membrane that performs membrane filtration separation processing at the following operating pressure, and the second RO device is an ultra-low pressure membrane filtration separation processing at an operating pressure of 0.7 MPa or less It is characterized by having an ultra-low pressure membrane module equipped with a low pressure membrane.
Further, the pure water production method of the present invention is characterized in that the product water has a removal rate of electrical conductivity with respect to the treated water of 98.5% or more.

According to the pure water production method and the pure water production system, raw water is softened with a soft water device so that the hardness is 5 mg CaCO ₃ / L or less to produce treated water, and the produced water silica for the treated water Since the water to be treated is treated with a reverse osmosis membrane while producing the production rate while monitoring the removal rate , the desired high purity pure water can be obtained , and the free chlorine in the soft water that is the water to be treated can be obtained . If the content is very small, it is possible to suppress the progress of the oxidative degradation of the RO membrane , and it is possible to quickly cope with the system abnormality caused by the oxidative degradation of the RO membrane due to the fluctuation of the silica removal rate .

  Further, since the free water contained in the raw water is removed by means of removing free chlorine such as an activated carbon filter, the water is softened, so that the treated water that has been softened does not contain free chlorine, or Even if free chlorine is contained in the water to be treated, it can be suppressed to a very small amount, and the progress of oxidative degradation of the RO membrane can be effectively suppressed.

Moreover, since the said production water has the removal rate of the electrical conductivity with respect to the said to-be-processed water 98.5% or more, it becomes possible to always supply the pure water which has desired high purity stably.

Production method and the pure water manufacturing system of the pure water, because the RO membrane operating pressure be composed of the following hypersonic low film 0.5 MPa, it is possible to drive the RO unit with a low operating pressure, thus the impurity Energy saving can be achieved while improving both the removal rate and the water recovery rate.

Further, after processing the treated water in the hypersonic low pressure membrane, since higher operating pressure of the salt rejection is treated in the following ultra low pressure membrane 0.7 MPa, to produce the product water, kept low operating pressure However, the removal rate can be further improved by the multi-stage RO treatment, and high-purity pure water can be efficiently obtained while saving energy.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system configuration diagram showing an embodiment (first embodiment) of a pure water production system used in a pure water production method according to the present invention.

  The pure water production system passes through a raw water pump 1 that supplies raw water such as ground water and tap water, an activated carbon filtration device (free chlorine removal means) 2 that removes free chlorine contained in the raw water, and an activated carbon filtration device 2. Water softener 3 that softens the raw water produced to produce treated water, RO device (reverse osmosis membrane filtration device) 4 that produces treated water by treating the treated water, and measures the flow rate of the produced water A flow meter 5 is sequentially disposed on a water supply line 6, and the water supply line 6 is connected to a water supply tank 7.

  Further, a residual chlorine measuring device 8 is disposed downstream of the activated carbon filtration device 2 to measure the concentration of free chlorine contained in the raw water, that is, free residual chlorine. Further, a hardness measuring device 9 is disposed downstream of the water softening device 3 and measures the hardness of the water to be treated discharged from the water softening device 3.

  First and second silica concentration measuring devices 10a and 10b are arranged on the upstream side and the downstream side of the RO device 4, respectively, and the removal rate of silica removed by the RO device 4 is the first and second silica. It is configured to be calculated based on the measurement results of the concentration measuring apparatuses 10a and 10b. Further, the water supply tank 7 has a pressure detection type water level sensor 11 inserted in the lower side wall thereof, and controls the supply of production water to the water supply tank 5 based on the detected water level of the water level sensor 11.

  Each of the above components is connected to a control unit (not shown), and the entire system is controlled by the control unit.

  The activated carbon filtration device 2 contains granular activated carbon (not shown) in the filtration tower, and removes free chlorine contained in the raw water. In addition, the activated carbon filtration device 2 has a built-in timer, and periodically stops the supply of raw water from the water supply line 6 to perform a regeneration process. That is, the regeneration mode is entered every predetermined time (for example, 1 to 7 / day), and the backwash pump (not shown) is driven to supply the production water stored in the feed water tank 7 to the activated carbon filtration device 2. After backwashing, it is washed with water after a lapse of a predetermined time to remove foreign matters such as dust adhering to the activated carbon and regenerated.

  This activated carbon filtration device 2 can be omitted depending on the quality of the raw water, for example, when the content of free chlorine contained in the raw water is very small. However, if the free chlorine is contained in a large amount in the raw water, or if an oxidizing agent such as sodium hypochlorite is intentionally injected into the raw water for the purpose of sterilizing microorganisms, the free chlorine should be removed. It is desirable to prevent oxidative deterioration of the RO membrane, and it is preferable to provide the activated carbon filtration device 2.

  In the regeneration mode, the product water in the water supply tank 7 is used for backwashing, but the raw water is supplied to the activated carbon filtration device 2 from a different line from the water supply line 6 and backwashed. Good.

In the water softener 3, a sodium-type cation exchange resin (not shown) is accommodated in an ion exchange tower, and saturated saline is stored in a salt water tank (not shown) attached to the ion exchange tower. Yes. When raw water is supplied from the water supply line 6 to the soft water device 3, hardness components contained in the raw water, that is, calcium ions and magnesium ions are ion-exchanged with sodium ions of the cation exchange resin to be removed. Is softened so that it becomes 5 mgCaCO ₃ / L or less. Moreover, when the exchange capacity of the cation exchange resin of the water softener 3 becomes saturated, the water softener 3 is switched from the water flow mode to the regeneration mode, and saturated saline is supplied from the salt water tank. Playback is performed. When the regeneration process is completed, the water supply mode is entered again, and raw water can be supplied.

Here, the reason for softening the water to be treated so that the hardness of the water to be treated is 5 mg CaCO ₃ / L or less is as follows.

If the hardness of the water to be treated exceeds 5 mg CaCO ₃ / L, when the water to be treated is supplied to the RO device 4, the hardness is too high to sufficiently remove impurities in the water to be treated. It becomes difficult to obtain high-purity pure water. In particular, from the viewpoint of energy saving, when an ultra-low pressure membrane having an operating pressure of 0.5 MPa or less is used as the RO membrane, the impurity removal rate may be reduced.

Therefore, in this embodiment, the hardness of the water to be treated is softened by the water softener 3 such that the following 5mgCaCO 3 / _L, doing this water to be treated.

In addition, by setting the hardness of the water to be treated to 5 mg CaCO ₃ / L or less in this way, even if free chlorine is contained in the water to be treated due to, for example, a decrease in the sorption ability of the activated carbon filtration device 2, If the content is very small, it is possible to suppress the progress of oxidative degradation of the RO membrane due to the free chlorine.

The form of the water softening device 3 is not particularly limited as long as it can be softened to 5 mgCaCO ₃ / L or less of water to be treated. For example, a cocurrent regeneration method in which both the water flow and the regenerative agent (saturated saline) flow in the same direction, a countercurrent regeneration method in which the water flow and the regenerant flow so as to face each other, water flow from one direction, Any split flow regeneration method that splits the regenerant to flow from both ends of the ion-exchange resin bed toward the center may be used, but even if the quality of the raw water is poor, that is, the residual salt concentration is high, It is preferable to employ a counter-current regeneration method or a split flow regeneration method that can stably ensure soft water of purity. In particular, the split flow regeneration method is more preferable because soft water having a target purity can be secured even when raw water is used instead of production water for extruding the regenerant.

  The RO device 4 includes a cross flow type RO membrane module 12 having a built-in RO membrane (RO membrane element) 12 a made of an ultra-low pressure membrane, and a pressure pump 13. The RO membrane module 12 is separated into a primary side through which the water to be treated flows and a secondary side that outputs permeated water that has passed through the RO membrane 12a. The primary side is an inflow port of the water to be treated and the water to be treated. Has a concentrated water outlet port. A drain valve 14 and a circulation line 15 are connected to the concentrated water outflow port so that a part of the concentrated water is discharged and the remainder is returned to the upstream side of the pressurizing pump 13.

The ultra-low pressure membrane is made of a synthetic polymer material such as polyamide, and has a permeation flux of 60 L / h · m ² · MPa or more at an operating pressure of 0.7 MPa with respect to a 500 mg / L NaCl aqueous solution at 25 ° C. It has a characteristic of a salt removal rate of 98.5% or more, and in this embodiment, the membrane filtration separation process is performed at an extremely low operating pressure of 0.5 MPa or less.

In the pure water production system configured as described above, the raw water supplied from the raw water pump 1 is supplied to the activated carbon filtration device 2, and free chlorine contained in the raw water is removed. Next, the residual chlorine measuring device 8 constantly monitors whether or not free chlorine is mixed in the raw water. If the content of free chlorine exceeds the allowable range (for example, 0.05 mgCl ₂ / L), it is determined that there is a possibility that the activated carbon filtration device 2 is abnormal, and system maintenance and inspection are performed. Do.

On the other hand, if the raw water contains no free chlorine or is contained within the allowable range even if it is contained, the raw water is supplied to the water softener 3. Then, the raw water is softened so that the water softening device 3 has a hardness of 5 mgCaCO ₃ / L or less to generate treated water.

Next, the water to be treated is measured by the hardness measuring device 9 to monitor whether the hardness does not exceed 5 mgCaCO ₃ / L. When the hardness of the water to be treated is greater than 5mgCaCO 3 / _L, it is determined that there is a possibility that abnormality in the water softener 3 has occurred, performs the maintenance and inspection of the system.

On the other hand, when the hardness of the water to be treated is 5 mgCaCO ₃ / L or less, the water to be treated is supplied to the RO device 4 via the water supply line 6.

  In the RO device 4, when the pressurizing pump 13 is driven, an operating pressure of 0.5 MPa or less is applied to the RO membrane 12a from the primary side, membrane separation is performed, and high-purity permeate flows out to the secondary side, Thereby, produced water is generated and stored in the water supply tank 7. A part of the concentrated water that has not permeated the RO membrane 12 a is returned to the upstream side of the pressurizing pump 13 through the circulation line 15, and the rest is drained from the drain valve 14.

  Further, the silica removal rate φ is calculated based on the following formula (1) by the first and second silica concentration measuring devices 10a and 10b arranged on the upstream side and the downstream side of the RO device 4, respectively.

φ = {(S1-S2) / S1} × 100 (1)
Here, S1 represents the silica concentration contained in the water to be treated, and S2 represents the silica concentration contained in the production water.

  By calculating the silica removal rate φ in this way, it is possible to discover oxidation deterioration of the RO film 12a at an early stage and avoid reduction in the removal rate due to oxidation deterioration of the RO film 12a as much as possible.

That is, as a method for monitoring the removal rate of various impurities, the electrical conductivity, ionic species such as Na ⁺ , Cl ⁻ , SO ₄ ²⁻ , or M alkalinity (necessary until the water to be treated reaches pH 4.8). It is also possible to monitor the amount of a simple acid in terms of calcium carbonate). However, when the quality of the water to be treated is monitored by the above ionic species, M alkalinity, etc., even if free chlorine is contained in the water to be treated, the removal rate of these impurities is that soft water is supplied as the water to be treated. As long as there is no change over time.

  On the other hand, in the case of silica, if free chlorine is contained in the water to be treated, the silica removal rate φ can be reduced from the beginning of water flow even when soft water is supplied to the RO device 4 as the water to be treated. It drops significantly in proportion to the water flow time.

  Therefore, it is preferable to monitor the silica removal rate φ with the first and second silica concentration measuring devices 10a and 10b, so that the oxidative deterioration of the RO membrane 12a can be detected at an early stage, and the system abnormality is promptly detected. Can deal with.

As described above, in the first embodiment, raw water is softened by the soft water device 3 so as to have a hardness of 5 mg CaCO ₃ / L or less to generate water to be treated, and the water to be treated is treated by the RO membrane 12a. As a result, production water is produced, so that it is possible to obtain desired high-purity pure water and to suppress the progress of oxidative degradation of the RO membrane.

  Further, since free chlorine contained in the raw water is removed by the activated carbon filtration device 2 and then softened by the water softening device 3, the softened water to be treated does not contain free chlorine, or even if it is covered. Even if free chlorine is contained in the treated water, it can be suppressed to a very small amount, and the progress of oxidative degradation of the RO membrane 12a can be effectively suppressed.

  Furthermore, since the silica removal rate φ of the produced water relative to the water to be treated is calculated based on the measurement results of the first and second silica concentration measuring devices 10a and 10b, the RO membrane 12a is caused by the fluctuation of the silica removal rate φ. This makes it possible to quickly cope with system abnormalities caused by oxidative degradation of the steel.

  In addition, since an ultra-low pressure membrane is used for the RO membrane 12a, it is possible to maintain a high removal rate and improve the water recovery rate even when operating at an operating pressure of 0.5 MPa or less, and energy saving operation Stable high-purity pure water can be obtained.

  FIG. 2 is a system configuration diagram showing a second embodiment of the pure water production system of the present invention.

  In the second embodiment, instead of the RO device 4 of the first embodiment, the first RO device 17 and the second RO device 19 are connected in series, and in the first RO device 17 The first RO film 16a is composed of an ultra-low pressure film, and the second RO film 18a in the second RO device 19 is composed of an ultra-low pressure film.

  That is, the first RO device 17 includes a cross flow type first RO membrane module 16 including a first RO membrane 16a made of an ultra-low pressure membrane, and a first pressurizing pump 20. Yes. The first RO membrane module 16 is separated into a primary side through which treated water flows and a secondary side that outputs permeated water that has passed through the first RO membrane 16a. A port and an outlet port for concentrated water in which the water to be treated is concentrated. A first drain valve 21 and a first circulation line 22 are connected to the concentrated water outflow port, and a portion of the concentrated water is drained while the remainder is returned to the upstream portion of the first pressurizing pump 20. It has become so.

The ultra-low pressure membrane is made of a synthetic polymer material such as polyamide, as in the first embodiment, and a permeation flux of 60 L / L at an operating pressure of 0.7 MPa with respect to a 500 mg / L NaCl aqueous solution at 25 ° C. It has characteristics of h · m ² · MPa or more and a salt removal rate of 98.5% or more, and in this embodiment, the membrane filtration separation process is performed at an operating pressure of 0.5 MPa or less.

The second RO device 19 includes a cross flow type second RO membrane module 18 incorporating a second RO membrane 18a made of an ultra-low pressure membrane, and a second pressurizing pump 23. . Similarly to the first RO membrane module 16, the second RO membrane module 18 is also divided into a primary side through which treated water flows and a secondary side that outputs permeated water that has passed through the second RO membrane 18a. The primary side has a treated water inflow port and a concentrated water outflow port in which the treated water is concentrated. The outlet port of the retentate, the second drain valve 24 and the second circulation line 25 is connected, a part of the concentrated water one drainage of columns to balance the upstream side of the second pressurizing pump 23 It is designed to be refluxed.

The ultra-low pressure membrane is made of a synthetic polymer material such as polyamide, and has a permeation flow rate of 45 L / h · m ² · MPa or more at an operating pressure of 0.75 MPa with respect to a 500 mg / L NaCl aqueous solution at 25 ° C. In this embodiment, the membrane filtration separation process is performed at an operation pressure of 0.7 MPa or less.

  In addition, first and second silica concentration measuring devices 26 a and 26 b are arranged on the upstream side and the downstream side of the first RO device 17, respectively, and the third silica concentration is arranged on the downstream side of the second RO device 19. A measuring device 26c is arranged. Then, based on the measurement results of the first and second silica concentration measuring devices 26a and 26b, the silica removal rate φ1 of the first RO membrane 16a is calculated, and the second and third silica concentration measuring devices 26b and 26c Based on the measurement result, the silica removal rate φ2 of the second RO film 18a is calculated, thereby monitoring the state of oxidative deterioration of the first RO film 16a and the second RO film 18a.

In the pure water production system configured in this way, after removing free chlorine with the activated carbon filtration device 2 as in the first embodiment, the raw water is softened to a hardness of 5 mg CaCO ₃ / L or less to generate treated water. Then, the treated water is supplied to the first RO device 17. And in the 1st RO apparatus 17, high purity pure water is produced | generated like 1st Embodiment, Furthermore, this pure water is supplied to the 2nd RO apparatus 19 as to-be-processed water.

  Since pure water has already been obtained in the first RO device 17 and the salt removal rate is higher in the second RO device 19 than in the first RO device 17, the impurity removal rate is further increased. be able to. Since pure water is supplied to the second RO device 19, high-purity pure water can be obtained at a pressure lower than the normal operating pressure, which can contribute to energy saving. In addition, since the ultra-low pressure membrane is used for the first RO membrane 16a, there is a margin in the capacity of the first pressurizing pump 20. For this reason, when the temperature is low, it is possible to easily increase the operation pressure by increasing the pump rotation speed, and it is possible to obtain the rated treated water amount.

Thus, also in the second embodiment, as in the first embodiment, raw water is softened by the water softening device 3 so as to have a hardness of 5 mg CaCO ₃ / L or less, and treated water is generated. Since the water to be treated is treated with the first RO membrane 16a of the ultra-low pressure membrane and the second RO membrane 18a of the ultra-low pressure membrane to produce the produced water, the impurity removal rate can be further increased. Therefore, it is possible to obtain pure water of higher purity with high efficiency while performing energy saving operation, and to suppress the progress of oxidative degradation of the RO membrane.

  Further, as in the first embodiment, after removing free chlorine contained in the raw water by the activated carbon filtration device 2, water softening is performed by the water softening device 3, so that free chlorine is contained in the treated water that has been softened. Even if free chlorine is not contained in the water to be treated, it can be suppressed to a very small amount, and the progress of oxidative degradation of the first and second RO membranes 16a and 18a can be effectively suppressed. Is possible.

  Further, since the silica removal rates φ1 and φ2 of the produced water relative to the water to be treated are calculated based on the measurement results of the first to third silica concentration measuring devices 26a to 26c, fluctuations in the silica removal rates φ1 and φ2 Thus, it becomes possible to quickly cope with the system abnormality caused by the oxidative deterioration of the first and second RO films 16a and 18a.

  The present invention is not limited to the above embodiment. In each of the above embodiments, free chlorine is removed by the activated carbon filtration device, but instead of the activated carbon filtration device, a reducing agent such as sodium bisulfite is injected into the raw water to reduce and remove free chlorine in the raw water. It may be.

  Next, examples of the present invention will be specifically described.

  In Example 1, the hardness of the test water as the water to be treated was changed, and the electrical conductivity removal rate (hereinafter referred to as “EC removal rate”) at each hardness was calculated. I investigated the relationship.

  In addition, EC removal rate means the electrical conductivity of permeated water when the electrical conductivity of the test water supplied to RO membrane is set to 100, and it computed by Numerical formula (2).

EC removal rate (%) = {(E1-E2) / E1} × 100 (2)
Here, E1 represents the electrical conductivity of the test water supplied to the RO membrane, and E2 represents the electrical conductivity of the permeated water.

  FIG. 3 is a schematic configuration diagram of the experimental apparatus used in Example 1.

  That is, this experimental apparatus includes a water supply tank 31 in which test water is stored and an RO membrane module 32. Further, first to third pressure gauges 33a to 33c are provided on the water supply side, the concentrated water side, and the permeate (product water) side of the RO membrane module 32, respectively. The water supply tank 31 and the RO membrane module 32 are connected by a water supply line 34, and a water supply pump 35 is interposed in the water supply line 34.

  The permeated water separated by membrane filtration in the RO membrane module 32 is collected in the feed water tank 31 through the permeate line 36, while a part of the concentrated water is returned to the feed water line 34 through the concentrated water circulation line 37. The remaining portion of the concentrated water is collected in the water supply tank 31 through the drain line 38. Thus, in this embodiment, since both concentrated water and permeated water are collected in the water supply tank 31, the quality of the test water in the water supply tank 31 is always kept constant.

  In addition, a heater 39 is attached to the water supply tank 31 and a water supply circulation line 40 is connected thereto. The feed water circulation line 40 is provided with a circulation pump 41 and a chiller 42. By adjusting the heater 39 and the chiller 42, the test water in the feed water tank 31 is always set to about 25 ° C. The In addition, flow meters 43a to 43c and valves 44a to 44d are arranged at appropriate places in the piping.

  Here, as the RO membrane 32a built in the RO membrane module 32, an ultra-low pressure membrane having the following performance was used.

[RO membrane performance]
Membrane material: Polyamide-based polymer Membrane area: 37.2 m ²
Permeation flux: 60 L / h · m ² · MPa or more Salt removal rate: 98.5% or more In addition, the characteristics of the RO membrane are as follows: For 500 mg / L NaCl aqueous solution, the operating pressure at 25 ° C. is 0.7 MPa, and the water recovery rate Is shown as 15%.

  Using the experimental apparatus configured as described above, the experiment was performed as follows.

  First, the test water previously treated by the activated carbon filtration device and the soft water device was stored in the water supply tank 31, and the chiller 42 and the heater 39 were adjusted so that the test water temperature was about 25 ° C. The reason why the test water temperature is made substantially constant is to avoid affecting the EC removal rate and the like because the viscosity of the water varies depending on the temperature.

  Next, the valve 44a was opened to drive the water supply pump 35, and the test water was supplied to the RO membrane module 32 while adjusting the frequency with an inverter (not shown) so that the amount of permeated water was 1000 L / h. The operating pressure fluctuated between 0.3 and 0.4 MPa, but it was confirmed that the operating pressure could be suppressed to 0.5 MPa or less.

  Subsequently, the test water was separated by membrane filtration into permeated water and concentrated water using the RO membrane 32 a, and the permeated water was collected in the water supply tank 31. For the concentrated water, the valve 44b and the valve 44c are operated so that the ratio of the permeated water to the waste water is about 7: 3, and the circulating water is returned to the water supply line 34 via the concentrated water circulation line 37, The drainage returned to the water supply tank 31 via the drainage line 38.

  And calcium chloride was added to the water supply tank 31, the hardness of the test water was variously set, and the test water was passed through the experimental apparatus by the method described above.

  The test water hardness is set by calculating the theoretical addition amount of calcium chloride in advance so that the test water hardness becomes a predetermined value, and appropriately adding the theoretical addition amount to the test water in the water tank 31. went.

  Then, using an ICP emission spectrometer (VISTA-MPX, manufactured by Seiko Instruments Inc.), the hardness of the test water was measured for each experiment. Furthermore, test water and permeated water were sampled for each experiment, and the electric conductivity was measured with an electric conductivity meter (CM-21P manufactured by Toa DKK), and the EC removal rate was calculated based on the measurement result.

  Table 1 shows test no. The test water hardness in 1-9, EC removal rate, and test water temperature are shown.

図４は試験水硬度とＥＣ除去率及び試験水温度との関係をプロットした図であり、図５は図４のＡ部拡大図、図６は図４のＢ部拡大図である。いずれも横軸が試験水硬度（ｍｇＣａＣＯ_３／Ｌ）、左縦軸がＥＣ除去率（％）、右縦軸が試験水温度（℃）であり、実線がＥＣ除去率、破線が試験水温度を示している。

4 is a graph plotting the relationship between the test water hardness, the EC removal rate, and the test water temperature, FIG. 5 is an enlarged view of a portion A in FIG. 4, and FIG. 6 is an enlarged view of a portion B in FIG. In each case, the horizontal axis is the test water hardness (mgCaCO ₃ / L), the left vertical axis is the EC removal rate (%), the right vertical axis is the test water temperature (° C.), the solid line is the EC removal rate, and the broken line is the test water temperature. Is shown.

As is apparent from Table 1 and FIGS. 4 to 6, the EC removal rate decreases as the test water hardness increases. And test no. 3 and 4, when the test water hardness was 4.8 mg CaCO ₃ / L, the EC removal rate was 98.6%, and 98.5% or more could be secured, but the test water hardness was 12.9 mg CaCO 3. _{At 3} / L, the EC removal rate was 98.4%, decreasing to less than 98.5%.

Therefore, in order to ensure the EC removal rate of 98.5% or more and stably supply high-purity pure water, the test water hardness, that is, the hardness of the water to be treated to be supplied to the RO apparatus is 5 mg CaCO _3. It was found that it was necessary to suppress to / L or less.

  In this example, calcium chloride is added to change the test water hardness. However, when calcium chloride is added, it is considered that both chloride ions and calcium ions increase. Therefore, it is unclear whether the decrease in EC removal rate is due to chloride ions or calcium ions.

  Therefore, in this example, sodium chloride or calcium chloride was separately added to the test water so that the electrical conductivity of the test water was the same, and a comparative test was performed. As a result, the electrical conductivity increased in any test by addition of sodium chloride or calcium chloride. However, although the EC removal rate decreased in the test in which calcium chloride was added, it did not decrease in the test in which sodium chloride was added. Therefore, it is considered that the addition of calcium chloride increases calcium ions and increases hardness, thereby reducing the EC removal rate.

  Thus, it was confirmed that the decrease in the EC removal rate was not due to an increase in chloride ions but was due to an increase in calcium ions.

And in order to secure EC removal rate of 98.5% or more and to obtain high purity pure water according to Example 1, it is necessary to soften the water to be treated to 5 mg CaCO ₃ / L or less. It was confirmed.

  In Example 2, the relationship between water flow time, permeation flux, and removal rate was investigated using soft water obtained by softening tap water as raw water, and tap water (hard water), and the effect of these on the oxidative degradation of RO membranes. It was confirmed.

  FIG. 7 is a schematic configuration diagram of an experimental apparatus used in Example 2.

  In this experimental apparatus, a water softening device 46 is arranged on the raw water supply line 45, and the soft water softened by the water softening device 46 is stored in a water supply tank 47 as test water. Further, the water supply tank 47 and the RO membrane module 48 are connected by a water supply line 49, and a water supply pump 50 is interposed in the water supply line 49.

  As the RO membrane 48a built in the RO membrane module 48, an ultra-low pressure membrane having the same performance as that of Example 1 was used.

  A bypass line 51 that bypasses the soft water device 46 is connected to the raw water supply line 45 so that the raw water containing free chlorine is supplied directly to the water supply tank 47 without passing through the soft water device 46.

  Then, the RO membrane module 48 separates the test water (or raw water) into permeated water and concentrated water by membrane filtration, and the permeated water is discharged to the permeated water line 52, while part of the concentrated water passes through the concentrated water circulation line 53. And the remaining portion of the concentrated water is drained from the drain line 54 to the outside.

  The RO membrane module 48 is provided with first to third pressure gauges 56a to 56c on the water supply side, the concentrated water side, and the permeate side, respectively, and further, flow meters 57a to 57c and a valve 58a are provided at appropriate positions in the piping. -58c are arranged.

It was 0.4 mg / L when the water which flows through the water supply line 49 was sampled and free chlorine was measured with the residual chlorine measuring device. Moreover, when the test water (soft water) stored in the water supply tank 47 was sampled and the hardness was measured with a hardness measuring device, it was 5 mgCaCO ₃ / L or less.

  Next, the test water containing such free chlorine was continuously passed through the RO membrane module 48 for a long time with the test water temperature being substantially constant as in Example 1, and the EC removal rate, silica removal rate, The permeation flux was measured, and the change with time was examined. The operating pressure fluctuated in the range of 0.18 to 0.40 MPa, but it was confirmed that the operating pressure could be suppressed to 0.5 MPa or less.

FIG. 8 shows the measurement results. The horizontal axis is the water passage time (h), the left vertical axis is the removal rate (%) and the permeation flux (L / h · m ² · MPa), and the right vertical axis is the test water temperature (° C.). (I) is the silica removal rate (%), (II) is the EC removal rate (%), (III) is the permeation flux (L / h · m ² · MPa), and (IV) is the test water temperature (° C.). Is shown. In the figure, T is a soft water supply section, that is, a section where test water that has been subjected to soft water treatment by the soft water device 46 is supplied. After the soft water supply section T has elapsed, the water passage is switched to the bypass line 51, and tap water (hard water), which is raw water, is directly supplied to the RO membrane module 48.

  As is apparent from FIG. 8, the permeation flux increases with the passage of water passage time. That is, even in the soft water supply section T, since free chlorine is not removed, free water is contained in the soft water, and as a result, the oxidative deterioration of the RO membrane 48a proceeds and the permeation flux increases. Yes. In addition, in the soft water supply section T, the EC removal rate has hardly changed, but the silica removal rate has decreased significantly in proportion to the water passage time from the beginning of water flow. And after progress of the soft water supply area T, at the time of switching to raw | natural water (hard water) supply, the permeation | transmission flux rises further and EC removal rate falls rapidly.

  That is, when the treatment water contains a considerable amount of free chlorine without performing the removal treatment of free chlorine, the oxidative deterioration of the RO membrane proceeds, but the EC removal rate hardly fluctuates. Therefore, even if the electrical conductivity is monitored, the state of oxidative degradation cannot be quickly grasped.

  On the other hand, the silica removal rate decreases with time from the initial stage of water flow in proportion to the water flow time. Therefore, by constantly monitoring the silica removal rate, it is possible to quickly grasp the oxidative deterioration caused by free chlorine, and it is possible to quickly cope with system abnormalities.

  In FIG. 9, the removal rate of sodium ions and sulfate ions is compared with the silica removal rate, the horizontal axis is the water passage time (h), and the vertical axis is the removal rate (%). (I) is the removal rate of silica, (II) is the sodium ion, and (III) is the removal rate of sulfate ion.

  The removal rate of sodium ions and sulfate ions was determined by measuring the sodium ion concentration and sulfate ion concentration of test water and permeated water by an ion chromatography method (ICS-1000 manufactured by Dionex). In addition, although the removal rate was calculated | required also about the chloride ion and M alkalinity, since the removal rate substantially the same as a sodium ion was shown, illustration was abbreviate | omitted.

  As is clear from FIG. 9, since the free water is contained in the soft water, the silica removal rate has decreased over time from the initial stage of water flow in proportion to the water flow time. As in the case of electrical conductivity (see FIG. 8), the removal rate of the ions hardly varies in the soft water supply section T.

  Therefore, it was found that when the treatment water contains a considerable amount of free chlorine, it is preferable to monitor the silica removal rate at all times to quickly cope with the oxidative deterioration of the RO membrane.

1 is a system configuration diagram showing one embodiment (first embodiment) of a pure water production system used in a pure water production method according to the present invention. It is a system block diagram which shows 2nd Embodiment of the pure water manufacturing system used for the manufacturing method of the pure water which concerns on this invention. 1 is a schematic configuration diagram of an experimental apparatus used in Example 1. FIG. It is a figure which shows the relationship between the hardness of to-be-processed water, EC removal rate, and to-be-processed water temperature. It is the A section enlarged view of FIG. FIG. 5 is a large view of part B of FIG. 4. 3 is a schematic configuration diagram of an experimental apparatus used in Example 2. FIG. It is a figure which shows the relationship between water flow time, a removal rate, a permeation | transmission flux, and to-be-processed water temperature. It is a figure which shows the relationship between water flow time and a removal rate.

Explanation of symbols

2 Activated carbon filter (free chlorine removal means)
3 Soft water device 4 RO device 10a 1st silica concentration measuring device 10b 2nd silica concentration measuring device 12a RO membrane (ultra-low pressure membrane)
16a First RO membrane (very low pressure membrane)
17 First RO device 18a Second RO membrane (ultra-low pressure membrane)
19 Second RO device 26a First silica concentration measuring device 26b Second silica concentration measuring device 26c Third silica concentration measuring device

Claims (11)

A method for producing pure water by treating water to be treated with a reverse osmosis membrane to produce product water,
Hardness and soften raw water so that less 5mgCaCO 3 / _L to produce a treated water, the process the water to be treated while monitoring the silica removal rate of the product water water to be treated by the reverse osmosis membrane method for producing pure water, characterized in that to generate the product water to.   The method for producing pure water according to claim 1, wherein the water softening is performed after removing free chlorine contained in the raw water. The method for producing pure water according to claim 1 or 2 , wherein the reverse osmosis membrane is an ultra-low pressure membrane that performs membrane filtration separation treatment at an operating pressure of 0.5 MPa or less . The reverse osmosis membrane includes at least two or more types including an ultra-low pressure membrane that performs membrane filtration separation treatment at an operating pressure of 0.5 MPa or less and an ultra-low pressure membrane that performs membrane filtration separation treatment at an operation pressure of 0.7 MPa or less. With
The pure water according to any one of claims 1 to 3, wherein the treated water is treated with the ultra-low pressure membrane and then treated with the ultra-low pressure membrane to produce the produced water. Production method. The method for producing pure water according to any one of claims 1 to 4, wherein the production water has a removal rate of electrical conductivity of 98.5% or more with respect to the water to be treated . In a pure water production system comprising a soft water device for softening raw water to produce treated water, and a reverse osmosis membrane filtration device for producing product water by treating the treated water produced by the soft water device,
A silica removal rate monitoring means for monitoring the silica removal rate of the production water relative to the raw water,
The water softener includes a pure water production system characterized in that it has a treatment water generating means for generating a treatment water to soften raw water so that less 5mgCaCO 3 / _L.   7. The pure water production system according to claim 6, further comprising free chlorine removing means for removing free chlorine contained in the raw water.   The pure water production system according to claim 7, wherein the free chlorine removing means is an activated carbon filtration device. The reverse osmosis membrane filtration apparatus includes an ultra-low pressure membrane module including an ultra-low pressure membrane that performs membrane filtration separation processing at an operating pressure of 0.5 MPa or less. Item 9. A pure water production system according to any one of Items 8 to 9. The reverse osmosis membrane filtration device comprises two or more types of reverse osmosis membrane filtration devices including a first reverse osmosis membrane filtration device and a second reverse osmosis membrane filtration device,
The first reverse osmosis membrane filtration device has an ultra-low pressure membrane module having an ultra-low pressure membrane that performs membrane filtration separation processing at an operating pressure of 0.5 MPa or less , and the second reverse osmosis membrane filtration device The ultra-low pressure membrane module comprising an ultra-low pressure membrane that performs membrane filtration separation processing at an operation pressure of 0.7 MPa or less. Water production system. The pure water production system according to any one of claims 6 to 10, wherein a removal rate of electrical conductivity with respect to the water to be treated is 98.5% or more.

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