JP2006130496A - Water treatment device and its operating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment device capable of preventing the reduction of a permeated water amount at the time of the water permeation operation and performing a stable long run even if raw water containing turbid components is permeated by selecting proper operating conditions and suitable membranes to regularly or irregularly perform back-pressure washing from a permeation water side in a water treatment device using a reverse osmosis membrane module or nano-filtering membrane module and a method of operating it. <P>SOLUTION: The water treatment device and the method of operating it in the method for operating the water treatment device in which permeated water and concentrated water are separated by supplying the raw water to the reverse osmosis membrane module and nano-filtering membrane module, for the surface roughness of the membrane used in a membrane element of the reverse osmosis membrane module or nano-filtering membrane module when unused, a membrane of difference between the highest point and lowest point in a straight line of arbitrary length of 1 μm on an even polymerization surface is 0.4 μm or less is used, and the membrane is regularly or irregularly back-pressure washed from the water permeation side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a water treatment apparatus and an operation method thereof, and more particularly to a water treatment apparatus and an operation method thereof that treat raw water using a reverse osmosis membrane module or a nanofiltration membrane module.

  Conventionally, for example, as a method for obtaining seawater desalination, ultrapure water, and water for various production processes, a module, for example, a spiral membrane element, used as a membrane for separating a reverse osmosis membrane or a nanofiltration membrane into permeated water and concentrated water There is known a water treatment apparatus that separates ionic components and low molecular components from raw water. Also, it is possible to separate low molecular or high molecular components, ultrafiltration that separates only high molecular components from low molecular or high molecular components, and microfiltration that separates fine particles. Partial spiral membrane elements are used. This spiral membrane element is formed, for example, by forming a bag-like membrane by laminating separation membranes on both sides of a permeate spacer and adhering three sides, and attaching the open end of the bag-like membrane to a permeate water collecting pipe, Along with the net-like raw water spacer, it is wound around the water collecting pipe in a spiral shape. The raw water path is formed by the raw water spacers disposed between the wound bag-like membranes. While flowing along the raw water spacer, the raw water is separated into permeated water that passes through the separation membrane and flows into the water collecting pipe through the permeated water spacer, and concentrated water that passes through the raw water spacer. Separation membrane modules equipped with such a spiral membrane element may be used as a single unit, and are used in parallel or in multiple stages to improve water recovery and throughput. Sometimes.

  When using a separation membrane module equipped with such a spiral membrane element to obtain seawater desalination, ultrapure water, and water for various manufacturing processes, pretreatment is usually performed for the purpose of removing turbidity in raw water. Has been done. This pretreatment is performed in a spiral membrane element, for example, a reverse osmosis membrane spiral element, because the thickness of the raw water spacer increases the contact area between the raw water and the reverse osmosis membrane as much as possible while securing the raw water flow path. However, the turbidity is usually less than 1 mm and accumulated in the raw water spacer in the raw water flow path, and the raw water flow path is likely to be blocked. This is to avoid an increase in the water differential pressure, a decrease in the amount of permeated water, and a decrease in the quality of the permeated water, so that stable operation can be performed for a long time. Such a pretreatment device used for the purpose of turbidity includes, for example, each device such as a coagulation sedimentation treatment, a filtration treatment or a membrane treatment, and these devices are the installation cost and operation cost of the entire water treatment system. In addition, there is a problem that a large installation area is required.

  By the way, if the pretreatment for the reverse osmosis membrane module or nanofiltration membrane module attached to the spiral membrane element can be omitted or simplified, the raw water containing turbidity can be supplied to the spiral membrane element without any pretreatment or by a simple method. The whole system can be simplified, the installation area can be reduced, and the cost can be reduced, and the industrial utility value is extremely high. However, if raw water containing turbidity is supplied directly to the spiral membrane element, serious problems such as an increase in the water flow differential pressure due to blockage of the raw water flow path and a decrease in the amount of permeate due to contaminants adhering to the membrane surface Will occur. In recent years, pressure reduction of reverse osmosis membranes and nanofiltration membranes has progressed, and polyamide (PA) type is often used as the material. Although the PA film can be reduced in pressure, it is weak against dirt and tends to adhere to the film surface with contaminants.

  In hollow fiber UF and MF, the amount of permeated water is maintained by regular backwashing. However, backwashing with a spiral membrane element is difficult due to its structure. In spiral-type UF, elements that can be partially back-pressure cleaned are put on the market. However, in spiral-type RO and NF, there are no elements intended for back-pressure cleaning.

  Patent Document 1 discloses a method of alternately flushing the primary side that is the raw water side from the inlet side and the outlet side. However, this method has the effect of suppressing the increase in the water flow differential pressure on the raw water side, but the effect of suppressing the decrease in the permeate flow rate is insufficient, and a decrease in the permeate flow rate is unavoidable due to long-term operation. It was.

Furthermore, Patent Document 2 discloses a method in which a flocculant is added to water containing a suspending substance and the like, water is passed through a membrane separator, and the membrane is back-pressure washed at intervals of 30 to 120 minutes. . However, this method is mainly intended for UF membranes, and when this method is applied to a normal spiral membrane element, aggregates due to the flocculant block the raw water flow path and increase the water flow differential pressure. , Driving itself could be difficult.
JP 2004-141864 A JP-A-2-265628

  An object of the present invention is to select an appropriate operating condition and an appropriate membrane in a water treatment apparatus using a reverse osmosis membrane module or a nanofiltration membrane module, and perform back pressure washing from the permeation side regularly or irregularly. An object of the present invention is to provide a water treatment apparatus capable of preventing a decrease in the amount of permeated water during permeation operation even when raw water containing turbidity is passed, and a method for operating the same, which can be stably operated for a long time.

  In order to solve the above problems, the operation method of the water treatment apparatus according to the present invention is an operation method of a water treatment apparatus that supplies raw water to a reverse osmosis membrane module or a nanofiltration membrane module to separate permeated water and concentrated water. The surface roughness when the membrane used in the membrane element of the reverse osmosis membrane module or the nanofiltration membrane module is not used is the highest vertex and the lowest point in a straight line having an arbitrary length of 1 μm on the uniform polymerization surface, Using a film having a difference in height (height difference) of 0.4 μm or less, and performing back pressure washing from the permeation side regularly or irregularly. By selecting such an element, effective back pressure cleaning can be performed and the amount of permeated water can be maintained. If it exceeds 0.4 μm, the recoverability of the amount of permeated water by back pressure cleaning will deteriorate.

  The term “uniformly polymerized surface” as used herein refers to a normal film surface. For example, the surface is uniform due to unevenness of the substrate surface, steps due to partial incomplete polymerization, physical defects, etc. Indicates the part excluding the difficult side. In other words, the “difference between the highest vertex and the lowest point in a straight line having an arbitrary length of 1 μm on the uniform polymerization surface” means the film surface on the film surface excluding a portion where a large level difference is caused by unevenness of the substrate surface. It shows the degree of unevenness on the surface. For example, in a reverse osmosis membrane made of a polyamide-based material, the expression “height of the folds on the membrane surface” is generally used. The membrane in the present invention includes not only a composite membrane such as a polyamide membrane but also an asymmetric membrane such as a membrane of a cellulose-based material, and the membrane surface may be a polymer.

  The surface roughness when the film is not used is such that the difference between the highest vertex and the lowest point in a straight line having an arbitrary length of 1 μm on the uniform polymerization surface is 0.4 μm or less, preferably 0.2 μm or less, more preferably 0 .1 μm or less. Thereby, it becomes possible to recover the amount of permeated water more effectively by back pressure cleaning. For example, in a spiral type membrane element, one leaf of the membrane is as large as about 1 m square, and it cannot be said that the whole is uniformly polymerized. It is better to observe a minute section with a length of about 1 μm and measure a uniform overlapping surface. For the measurement, a scanning electron microscope (SEM) or an atomic force microscope (AFM) can be used.

In order to solve the above-mentioned problem, another method for operating a water treatment apparatus according to the present invention is a method of supplying raw water to a reverse osmosis membrane module or a nanofiltration membrane module and separating it into permeated water and concentrated water. In the operation method of the treatment apparatus, a permeate flow of 0.7 m ³ / (m ² · day) or more at a supply pressure of 0.5 MPa is applied to the membrane used in the membrane element of the reverse osmosis membrane module or the nanofiltration membrane module. A membrane capable of obtaining a bundle is used, and back pressure cleaning is performed from the permeation side regularly or irregularly. By using a membrane element that can obtain a relatively high amount of permeated water at a low pressure in this way, a large amount of backwashing water can be obtained during backwashing, and the recoverability is improved. If it becomes 0.7 m ³ / (m ² · day) or less at a supply pressure of 0.5 MPa, the amount of backwashing water is small, and there is a possibility that the recoverability of the amount of permeated water by backwashing may deteriorate.

  At the time of the reverse pressure cleaning, it is preferable to discharge the cleaning water to the raw water supply side to the reverse osmosis membrane module or the nanofiltration membrane module during the permeation operation. That is, since the inlet side of the raw water to the module is most easily contaminated during the permeation operation, the pollutants accumulated on the inlet side of the raw water to the module can be efficiently removed by forming the flow path as described above.

  The pressure at the time of the back pressure cleaning is set to 1 to 99% (preferably 10 to 80%, more preferably 20 to 60%) of the operating pressure, and does not exceed 0.5 MPa. It is desirable to set. Thus, by setting an appropriate pressure at the time of back pressure cleaning, the element can be prevented from being damaged and repeated back pressure cleaning can be performed. If it is less than 1% of the operating pressure, the pressure is too low, water does not flow, and backwashing itself cannot be performed. If it exceeds 50% or exceeds 0.5 MPa, the membrane may be damaged.

  In the case of a regular period, the back pressure cleaning interval is preferably performed once every 10 minutes to 24 hours. Thereby, an appropriate cleaning interval is set, and stable operation is possible. If it is less than 10 minutes, it is too frequent and may cause a reduction in water recovery rate and a shortened membrane life. On the other hand, if it exceeds 24 hours, the recoverability of the amount of permeated water may gradually deteriorate.

  In the case of irregular intervals, it is preferable to carry out the back pressure cleaning at the time when the reduction rate is set in advance, which is 1 to 20% lower than the amount of permeated water immediately after the previous cleaning. Thereby, an appropriate cleaning interval is set, and stable operation is possible. If it is less than 1%, it is too frequent and may cause a decrease in water recovery rate and shortening of membrane life. On the other hand, if it exceeds 20%, the recoverability of the permeated water amount may be gradually deteriorated.

  It is preferable to set the cleaning time for the back pressure cleaning to 15 to 120 seconds. Effective back pressure cleaning can be performed with appropriate settings. If it is less than 15 seconds, the washing is insufficient, and the permeated water amount may not be recovered sufficiently. On the other hand, if it exceeds 120 seconds, the water recovery rate may be reduced and the membrane life may be shortened.

  It is preferable to use permeated water as the washing water for the back pressure washing. By using permeated water, effective back pressure cleaning can be performed.

  As the reverse osmosis membrane or nanofiltration membrane, a flat membrane, a hollow fiber membrane, a tubular membrane or the like can be used. However, use of a spiral membrane element is preferable because a cheaper system can be provided.

  As the raw water, raw water having an FI value (Fouling Index) of 4 or more can be used. Normally, in the spiral membrane element, the upper limit of the FI value is set low and the raw water conditions are limited. However, according to the present invention, even if the raw water has an FI value of 4 or more, direct reverse osmosis filtration or nanofiltration is performed. Can be processed. In the present application, “directly” means that the water to be treated is treated as it is without adding a flocculant to the raw water in advance or performing filtration as a pretreatment for introducing the raw water into the system of the water treatment apparatus. Introducing into the system of the device means reverse osmosis filtration or nanofiltration. However, if coarse particles of 0.5 mm or more are mixed, there is a risk of physical damage to the element, so it is preferable to remove the coarse particles in advance. Coarse particles can be removed with a simple strainer or the like. The raw water is not particularly limited as long as it normally requires turbidity, and examples thereof include groundwater, well water, river water, lake water, rain water, industrial water, tap water, and treated sewage water. The FI value is sometimes called an SDI value.

  Moreover, you may add dispersing agents, such as a scale inhibitor and a fouling inhibitor, to the said raw | natural water. Thereby, accumulation of turbidity on both the raw water spacer and the membrane surface can be further suppressed, and the recoverability by back pressure cleaning is further improved. The dispersing agent to be used is not particularly limited, and examples thereof include Hypersperse MSI300 and Hypersperse MDC200 manufactured by ARGO SCIENTIFIC.

  In order to solve the above-described problems, the water treatment device according to the present invention supplies the raw water to the reverse osmosis membrane module or the nanofiltration membrane module, and in the operation of the water treatment device that separates the permeated water and the concentrated water, When the membrane used in the membrane element of the osmosis membrane module or the nanofiltration membrane module is not used, the difference between the highest vertex and the lowest point in the straight line with an arbitrary length of 1 μm on the uniform polymerization surface is 0. It is characterized by using a membrane having a thickness of 4 μm or less and having means for back-pressure cleaning from the permeation side at regular or irregular intervals. By selecting such an element, effective back pressure cleaning can be performed and the amount of permeated water can be maintained. If it exceeds 0.4 μm, the recoverability of the amount of permeated water by back pressure cleaning will deteriorate.

  The surface roughness when the film is not used is such that the difference between the highest vertex and the lowest point in a straight line having an arbitrary length of 1 μm on the uniform polymerization surface is 0.4 μm or less, preferably 0.2 μm or less, more preferably 0. .1 μm or less. Thereby, it becomes possible to recover the amount of permeated water more effectively by back pressure cleaning. For example, in a spiral type membrane element, one leaf of the membrane is as large as about 1 m square, and it cannot be said that the whole is uniformly polymerized. It is better to observe a minute section with a length of about 1 μm and measure a uniform overlapping surface. For the measurement, a scanning electron microscope (SEM) or an atomic force microscope (AFM) can be used.

In order to solve the above-mentioned problem, another water treatment device according to the present invention is a water treatment device for supplying raw water to a reverse osmosis membrane module or a nanofiltration membrane module and separating it into permeated water and concentrated water. In operation, a membrane capable of obtaining a permeation flux of 0.7 m ³ / (m ² · day) or more at a supply pressure of 0.5 MPa to the membrane used in the membrane element of the reverse osmosis membrane module or nanofiltration membrane module And having means for back-pressure cleaning from the permeation side at regular or irregular intervals. By using a membrane element that can obtain a relatively high amount of permeated water at a low pressure in this way, a large amount of backwashing water can be obtained during backwashing, and the recoverability is improved. If it becomes 0.7 m ³ / (m ² · day) or less at a supply pressure of 0.5 MPa, the amount of backwashing water is small, and there is a possibility that the recoverability of the amount of permeated water by backwashing may deteriorate.

  At the time of the reverse pressure cleaning, it is preferable to discharge the cleaning water to the raw water supply side to the reverse osmosis membrane module or the nanofiltration membrane module during the permeation operation. That is, since the inlet side of the raw water to the module is most easily contaminated during the permeation operation, the pollutants accumulated on the inlet side of the raw water to the module can be efficiently removed by forming the flow path as described above.

  The pressure at the time of the back pressure cleaning is set to 1 to 99% (preferably 10 to 80%, more preferably 20 to 60%) of the operating pressure, and does not exceed 0.5 MPa. It is desirable to set. Thus, by setting an appropriate pressure at the time of back pressure cleaning, the element can be prevented from being damaged and repeated back pressure cleaning can be performed. If it is less than 1% of the operating pressure, the pressure is too low, water does not flow, and backwashing itself cannot be performed. If it exceeds 50% or exceeds 0.5 MPa, the membrane may be damaged.

  In the case of a regular period, the back pressure cleaning interval is preferably performed once every 10 minutes to 24 hours. Thereby, an appropriate cleaning interval is set, and stable operation is possible. If it is less than 10 minutes, it is too frequent and may cause a reduction in water recovery rate and a shortened membrane life. On the other hand, if it exceeds 24 hours, the recoverability of the amount of permeated water may gradually deteriorate.

  In the case of irregular intervals, it is preferable to carry out the back pressure cleaning at the time when the reduction rate is set in advance, which is 1 to 20% lower than the amount of permeated water immediately after the previous cleaning. Thereby, an appropriate cleaning interval is set, and stable operation is possible. If it is less than 1%, it is too frequent and may cause a decrease in water recovery rate and shortening of membrane life. On the other hand, if it exceeds 20%, the recoverability of the permeated water amount may be gradually deteriorated.

  It is preferable to set the cleaning time for the back pressure cleaning to 15 to 120 seconds. Effective back pressure cleaning can be performed with appropriate settings. If it is less than 15 seconds, the washing is insufficient, and the permeated water amount may not be recovered sufficiently. On the other hand, if it exceeds 120 seconds, the water recovery rate may be reduced and the membrane life may be shortened.

  It is preferable to use permeated water as the washing water for the back pressure washing. By using permeated water, effective back pressure cleaning can be performed.

  As the reverse osmosis membrane or nanofiltration membrane, a flat membrane, a hollow fiber membrane, a tubular membrane or the like can be used. However, use of a spiral membrane element is preferable because a cheaper system can be provided.

  As the raw water, raw water having an FI value (Fouling Index) of 4 or more can be used. Normally, in the spiral membrane element, the upper limit of the FI value is set low and the raw water conditions are limited. However, according to the present invention, even when the raw water has an FI value of 4 or more, direct reverse osmosis filtration or nanofiltration is performed. Can be processed. However, if coarse particles of 0.5 mm or more are mixed, there is a risk of physical damage to the element, so it is preferable to remove the coarse particles in advance. Coarse particles can be removed with a simple strainer or the like. The raw water is not particularly limited as long as it normally requires turbidity, and examples thereof include groundwater, well water, river water, lake water, rain water, industrial water, tap water, and treated sewage water.

  Moreover, you may add dispersing agents, such as a scale inhibitor and a fouling inhibitor, to the said raw | natural water. Thereby, accumulation of turbidity on both the raw water spacer and the membrane surface can be further suppressed, and the recoverability by back pressure cleaning is further improved. The dispersing agent to be used is not particularly limited, and examples thereof include Hypersperse MSI300 and Hypersperse MDC200 manufactured by ARGO SCIENTIFIC.

  In the water treatment apparatus and the operation method thereof according to the present invention, it is possible to suppress a decrease in the amount of permeated water over time during the permeation operation, and the apparatus can be stably operated for a long period of time.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The embodiment described below shows an example of the invention and does not limit the content of the invention.
With reference to FIG. 1, a method of operating the separation membrane module in the embodiment of the present invention will be described. In FIG. 1, some pressure gauges, flow meters, valves, and the like that are not necessary for explanation are omitted.

  In FIG. 1, 1 is a raw water pump, 2 is a separation membrane module, 3 is a back pressure washing pump, 4 is a permeated water storage tank, 10 to 26 are piping, and 50 to 55 are valves.

  During normal operation (step A), the valves 50 and 53 are opened, the valve 52 is adjusted to a predetermined pressure and flow rate, and the other valves are closed. Raw water is supplied from the pipe 10 to the pump 1, boosted, and sent to the separation membrane module 2 through the pipe 11 → the pipe 12 → the pipe 13. The concentrated water and permeated water are separated in the module, and the concentrated water flows from pipe 20 to pipe 21 to pipe 22 and is blown or sent to a second-stage separation membrane device or the like. The permeated water is stored in the permeated water storage tank 4 via the pipe 14 → the pipe 15 → the pipe 16 and is used as it is or is sent to a subsystem in the subsequent stage.

  During normal operation, it is recommended to perform flushing periodically. Although the effect of suppressing the decrease in the permeated water amount / rejection rate by the flushing is low, the effect of alleviating clogging of the raw water channel can be expected. The flushing interval is preferably about once every 10 minutes to 24 hours, and the flushing time is preferably about 30 seconds to 120 seconds. At the time of flushing, in step A, the valve 51 is fully opened, and the flow rate flowing to the primary side of the module is increased at a stroke.

  If predetermined time passes, the pump 1 will be stopped and it will enter into a back pressure washing | cleaning process (process B-1). The valves 51 and 54 are open, and the other valves are closed. Back pressure washing water (permeated water) is supplied from the pipe 19 to the pump 3 and sent to the permeation side (secondary side) of the separation membrane module 2 via the pipe 18 → the pipe 17 → the pipe 14. This water permeates through the membrane from the secondary side to the primary side (raw water side), strips off the contaminants attached to the membrane, flows through the pipe 20 → pipe 23 → pipe 24, and is blown.

  Then, after a predetermined cleaning time has elapsed, the process returns to step A, and this is repeated thereafter.

  However, when the back pressure washing process of process B-1 is repeated over a long period of time, the raw water flow path may be blocked over time. Therefore, step B-2 shown below may be performed instead of step B-1. That is, in step B-2, the valves 54 and 55 are opened, and the other valves are closed. Water for reverse pressure cleaning (permeated water) is supplied from 19 to the pump 3 and sent to the permeation side (secondary side) of the separation membrane module 2 via the pipe 18 → the pipe 17 → the pipe 14. This water permeates through the membrane from the secondary side to the primary side (raw water supply side), strips off contaminants adhering to the membrane, flows through the pipe 13 → the pipe 25 → the pipe 26, and is blown.

  The difference between the process B-1 and the process B-2 is the water outlet at the time of back pressure cleaning. During operation, the raw water inlet side (raw water supply side) is most likely to be contaminated, so according to Step B-2, the pollutant in the raw water flow path is taken out from the module by creating a flow opposite to that during operation. be able to.

  The above operation may be performed by automatic control using a sequencer and an automatic valve.

  The above example shows the case where there is one module, but the present invention may be applied to an apparatus using a plurality of modules in parallel or in series.

  EXAMPLES Next, although an Example is given and this invention is demonstrated further more concretely, this is only an illustration and does not restrict | limit this invention.

Example 1
Industrial water having a turbidity of 1 degree and an electrical conductivity of 20 mS / m is treated with the flow apparatus shown in FIG. 1, and the above-described method (process A to process B-2) is used for 2000 hours of durable operation under the following operating conditions. went. The separation membrane module has a height difference of 0.05 μm between the highest vertex and the lowest point in a straight line with an arbitrary length of 1 μm, and a permeability of 1.2 m ³ / (m ² · day) at a supply pressure of 0.5 MPa. A spiral nanofiltration membrane element (8 inches) that can provide a flux was used. The performance evaluation of the separation membrane module was performed by measuring the water flow differential pressure, the permeated water amount, and the rejection rate at the initial stage of operation and 2000 hours.

(Operating conditions)
The operating conditions in step A are an operating pressure of 0.3 MPa, a concentrated water amount of 2.7 m ³ / hr, a water temperature of 25 ° C., and raw water pH = 7. Step A A 30-second back pressure cleaning (step B-2) was performed every 30 minutes. The pressure at the time of back pressure washing was 0.2 MPa. The module was flushed once every 10 minutes. The amount of concentrated water during flushing is about three times that during operation.

Example 2
Industrial water having a turbidity of 1 degree and an electrical conductivity of 20 mS / m is treated with the flow apparatus shown in FIG. 1, and the above-described method (process A to process B-2) is used for 2000 hours of durable operation under the following operating conditions. went. The separation membrane module has a height difference of 0.2 μm and a spiral nanofiltration membrane element (8 inches) that can obtain a permeation flux of 0.5 m ³ / (m ² · day) at a supply pressure of 0.5 MPa. It was used. The performance evaluation of the separation membrane module was performed by measuring the water flow differential pressure, the permeated water amount, and the rejection rate at the initial stage of operation and 2000 hours.

(Operating conditions)
The operating conditions in step A are an operating pressure of 0.75 MPa, a concentrated water amount of 2.7 m ³ / hr, a water temperature of 25 ° C., and raw water pH = 7. Step A A 30-second back pressure cleaning (step B-2) was performed every 30 minutes. The pressure during back pressure washing was 0.3 MPa. The module was flushed once every 10 minutes. The amount of concentrated water during flushing is about three times that during operation.

Example 3
Industrial water with a turbidity of 1 degree and conductivity of 20 mS / m is treated with the apparatus of the flow shown in FIG. 1, and the above method (Step A to Step B-2) is used for 2000 hours of durability operation under the following operating conditions. went. The separation membrane module has a height difference of 0.4 μm and a spiral type reverse osmosis membrane element (8 inches) that can obtain a permeation flux of 0.5 m ³ / (m ² · day) at a supply pressure of 0.5 MPa. It was used. The performance evaluation of the separation membrane module was performed by measuring the water flow differential pressure, the permeated water amount, and the rejection rate at the initial stage of operation and 2000 hours.

(Operating conditions)
The operating conditions in step A are an operating pressure of 0.75 MPa, a concentrated water amount of 2.7 m ³ / hr, a water temperature of 25 ° C., and raw water pH = 7. Step A A 30-second back pressure cleaning (step B-2) was performed every 30 minutes. The pressure during back pressure washing was 0.3 MPa. The module was flushed once every 10 minutes. The amount of concentrated water during flushing is about three times that during operation.

Example 4
Industrial water having a turbidity of 1 degree and an electrical conductivity of 20 mS / m is treated with the flow apparatus shown in FIG. 1, and the above-described method (process A to process B-2) is used for 2000 hours of durable operation under the following operating conditions. went. The separation membrane module has a height difference of 0.5 μm, and a spiral reverse osmosis membrane element (8 inches) that can obtain a permeation flux of 0.8 m ³ / (m ² · day) at a supply pressure of 0.5 MPa. It was used. The performance evaluation of the separation membrane module was performed by measuring the water flow differential pressure, the permeated water amount, and the rejection rate at the initial stage of operation and 2000 hours.

(Operating conditions)
The operating conditions in step A are an operating pressure of 0.5 MPa, an amount of concentrated water of 3.4 m ³ / hr, a water temperature of 25 ° C., and raw water pH = 7. Step A A 30-second back pressure cleaning (step B-2) was performed every 30 minutes. The pressure during back pressure washing was 0.3 MPa. The module was flushed once every 10 minutes. The amount of concentrated water during flushing is about three times that during operation.

Comparative Example 1
The same conditions as in Example 1 were set, and only Step A was performed, and the water flow differential pressure, the permeated water amount, and the rejection rate were measured.

(Operating conditions)
The operating conditions in step A are an operating pressure of 0.3 MPa, a concentrated water amount of 2.7 m ³ / hr, a water temperature of 25 ° C., and raw water pH = 7. The module was flushed once every 10 minutes. The amount of concentrated water during flushing is about three times that during operation.

Comparative Example 2
Industrial water having a turbidity of 1 degree and an electrical conductivity of 20 mS / m is treated with the flow apparatus shown in FIG. 1, and the above-described method (process A to process B-2) is used for 2000 hours of durable operation under the following operating conditions. went. The separation membrane module has a height difference of 0.5 μm, and a spiral nanofiltration membrane element (8 inches) that can obtain a permeation flux of 0.5 m ³ / (m ² · day) at a supply pressure of 0.5 MPa. It was used. The performance evaluation of the separation membrane module was performed by measuring the water flow differential pressure, the permeated water amount, and the rejection rate at the initial stage of operation and 2000 hours.

(Operating conditions)
The operating conditions in step A are an operating pressure of 0.75 MPa, a concentrated water amount of 2.7 m ³ / hr, a water temperature of 25 ° C., and raw water pH = 7. Step A A 30-second back pressure cleaning (step B-2) was performed every 30 minutes. The pressure during back pressure washing was 0.3 MPa. The module was flushed once every 10 minutes. The amount of concentrated water during flushing is about three times that during operation.

Comparative Example 3
Industrial water having a turbidity of 1 degree and an electrical conductivity of 20 mS / m is treated with the flow apparatus shown in FIG. 1, and the above-described method (process A to process B-2) is used for 2000 hours of durable operation under the following operating conditions. went. The separation membrane module has a height difference of 0.6 μm and a spiral type reverse osmosis membrane element (8 inches) that can obtain a permeation flux of 0.5 m ³ / (m ² · day) at a supply pressure of 0.5 MPa. It was used. The performance evaluation of the separation membrane module was performed by measuring the water flow differential pressure, the permeated water amount, and the rejection rate at the initial stage of operation and 2000 hours.

(Operating conditions)
The operating conditions in step A are an operating pressure of 0.75 MPa, a concentrated water amount of 2.7 m ³ / hr, a water temperature of 25 ° C., and raw water pH = 7. Step A A 30-second back pressure cleaning (step B-2) was performed every 30 minutes. The pressure during back pressure washing was 0.3 MPa. The module was flushed once every 10 minutes. The amount of concentrated water during flushing is about three times that during operation.

  The above results are summarized in Table 1 below.

  In Comparative Example 1 in which no back pressure cleaning was performed, a significant performance degradation occurred by about 800 hr, and it was difficult to continue the operation. Further, in Comparative Example 2 using a membrane having a relatively large difference in height, recovery by back pressure cleaning was insufficient. Even in Comparative Example 3 using a membrane having a relatively large height difference and a relatively low permeation flux, recovery by back pressure washing was insufficient. On the other hand, in Examples 1 to 4 using the method of the present invention, good treatment was possible.

  The water treatment apparatus and the operation method thereof according to the present invention can be applied to any water treatment apparatus that treats raw water using a reverse osmosis membrane module or a nanofiltration membrane module. Is preferred.

It is a schematic equipment system diagram of the water treatment equipment concerning one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water pump 2 Separation membrane module 3 Back pressure washing pump 4 Back pressure washing pump 10-26 Piping 50-55 Valve

Claims (22)

  In a method for operating a water treatment apparatus that supplies raw water to a reverse osmosis membrane module or a nanofiltration membrane module and separates it into permeated water and concentrated water, it is used for the membrane element of the reverse osmosis membrane module or nanofiltration membrane module The surface roughness when the film is not used is a film whose difference between the highest vertex and the lowest point in a straight line having an arbitrary length of 1 μm on the uniform polymerization surface is 0.4 μm or less, and is periodically or irregularly. A method for operating a water treatment apparatus, wherein back pressure washing is performed from the permeate side. In a method for operating a water treatment apparatus that supplies raw water to a reverse osmosis membrane module or a nanofiltration membrane module and separates it into permeated water and concentrated water, it is used for the membrane element of the reverse osmosis membrane module or nanofiltration membrane module A membrane capable of obtaining a permeation flux of 0.7 m ³ / (m ² · day) or more at a supply pressure of 0.5 MPa is used as the membrane, and back pressure washing is performed from the permeation side regularly or irregularly. The operation method of the water treatment equipment.   The operation method of the water treatment apparatus according to claim 1 or 2, wherein the washing water is discharged to the raw water supply side to the reverse osmosis membrane module or the nanofiltration membrane module during the permeation operation during the back pressure washing.   The water according to any one of claims 1 to 3, wherein the pressure at the time of back pressure washing is set to 1 to 99% of the pressure at the time of permeation operation and is set to a value not exceeding 0.5 MPa. Operation method of the processing apparatus.   The operation method of the water treatment apparatus according to any one of claims 1 to 4, wherein a cleaning interval at the time of the counter pressure cleaning performed regularly is once every 10 minutes to 24 hours.   The back pressure washing performed irregularly is performed at a time point when a reduction rate set in advance is reached when the permeated water amount immediately after the previous washing is reduced by 1 to 20%. The operation method of the water treatment apparatus as described.   The operation method of the water treatment apparatus according to any one of claims 1 to 6, wherein a cleaning time of the back pressure cleaning is 15 to 120 seconds.   The operation method of the water treatment apparatus according to any one of claims 1 to 7, wherein the permeated water is used as the washing water for the back pressure washing.   The operation method of the water treatment apparatus according to any one of claims 1 to 8, wherein a spiral membrane element is used as the reverse osmosis membrane module or the nanofiltration membrane module.   The method for operating a water treatment apparatus according to claim 1, wherein raw water having an FI value of 4 or more is used as the raw water.   The operation method of the water treatment apparatus according to claim 10, wherein the raw water is directly subjected to membrane filtration.   Membranes used for membrane elements of the reverse osmosis membrane module or nanofiltration membrane module in the operation of a water treatment device that supplies raw water to the reverse osmosis membrane module or nanofiltration membrane module and separates it into permeated water and concentrated water When the film is not used, a film having a surface roughness of 0.4 μm or less between the highest vertex and the lowest point in a straight line with an arbitrary length of 1 μm on a uniform polymerization surface is used, and the above-mentioned transmission is performed regularly or irregularly. A water treatment apparatus comprising means for back pressure washing from the side. Membrane used for the membrane element of the reverse osmosis membrane module or nanofiltration membrane module in the operation of a water treatment device that supplies raw water to the reverse osmosis membrane module or nanofiltration membrane module and separates it into permeated water and concentrated water Using a membrane capable of obtaining a permeation flux of 0.7 m ³ / (m ² · day) or more at a supply pressure of 0.5 MPa, and having means for back-pressure washing from the permeation side at regular or irregular intervals. A water treatment device characterized.   The water treatment device according to claim 12 or 13, further comprising means for discharging the wash water to the raw water supply side to the reverse osmosis membrane module or the nanofiltration membrane module during the permeation operation during the reverse pressure washing.   The pressure at the time of the back pressure washing is set to 1 to 99% of the pressure at the time of the permeation operation, and is set to a value not exceeding 0.5 MPa. Water treatment equipment.   The water treatment device according to any one of claims 12 to 15, wherein a cleaning interval at the time of the counter pressure cleaning performed periodically is set to once every 10 minutes to 24 hours.   The back pressure washing performed irregularly is performed at a time point when a reduction rate set in advance is reached when the permeated water amount immediately after the previous cleaning is reduced by 1 to 20%. The water treatment apparatus as described in.   The water treatment apparatus according to any one of claims 12 to 17, wherein a cleaning time for the back pressure cleaning is set to 15 to 120 seconds.   The water treatment apparatus according to any one of claims 12 to 18, wherein the permeated water is used as the washing water for the back pressure washing.   The water treatment apparatus according to any one of claims 12 to 19, wherein the reverse osmosis membrane module or the nanofiltration membrane module comprises a spiral membrane element.   The water treatment apparatus according to any one of claims 12 to 20, wherein the raw water is made of raw water having an FI value of 4 or more.   The water treatment apparatus according to claim 21, wherein the raw water is directly membrane-filtered.

Images