JP2012250180A - Prediction method for clogging speed of filtration membrane, and filtration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a prediction method for the clogging speed of a membrane capable of predicting the treated amount or operation time for generation of clogging of a membrane based on a measured value, the measured value being obtained by carrying out a measurement on water to be treated, in membrane filtration of water to be treated containing jelly-like suspended components such as seawater, drainage, ballast water, or the like, and also to provide a filtration system capable of carrying out the prediction method.SOLUTION: In membrane filtration, the prediction method for the clogging speed of a filtration membrane includes: measuring the sugar volume in the water to be treated such as seawater or the like; and calculating the clogging speed of a filtration membrane from the measured value, the measurement of the sugar volume being especially carried out by liquid chromatography for concentrated water to be treated, and the filtration system capable of carrying out the prediction method is also provided.

Description

  The present invention relates to a method for predicting the clogging speed of a filtration membrane, which enables prediction of the time when the filtration membrane needs to be washed based on the measurement value relating to the water to be treated in membrane filtration of seawater and the like, and the prediction method thereof It is related with the filtration system which can perform.

  In seawater desalination and wastewater treatment, membrane filtration using filtration membranes such as hollow fibers and membranes is widely performed to remove turbid components contained in treated water such as seawater, wastewater, and ballast water. Yes. During the operation of membrane filtration, pores of the filtration membrane are clogged by turbid components, and the treatment flow rate decreases and the filtration pressure increases over time.

  In particular, seawater contains about 1 to several ppm of a jelly-like adhesive substance called TEP (transparent epoxide polymer particles) that is secreted by plankton and microorganisms outside the cell, and this is the surface of the filtration membrane. In many cases, it sticks to the inside of the hole and spreads to clog the fouling (fouling), resulting in a decrease in processing flow rate (increase in filtration pressure). Therefore, it is necessary to clean the filtration membrane at a predetermined time during operation in order to eliminate clogging of the holes and restore the treatment flow rate and filtration pressure.

  Examples of the method for washing the filtration membrane include water backwashing and the like in which the washing water is flowed in the direction opposite to the flow of the water to be treated. Also, a method of cleaning the membrane by injecting a chemical solution (chemical solution cleaning), a method of cleaning the filter membrane by hand, and a method of cleaning by passing gas through the filter membrane in the direction opposite to the flow of the liquid during filtration Physical cleaning such as (air backwashing), a method of washing by applying ultrasonic waves to the film (ultrasonic cleaning), and the like are also employed. In order to further increase the cleaning efficiency, cleaning methods combining these are also known.

  For example, Patent Document 1 states, “While applying mechanical vibration to a filter module using a hollow fiber membrane, backwash water is passed through the filter module to oscillate the water in the module and adhere to the filtration surface. The method for regenerating the filter module is characterized by changing the water level in the module along the hollow fiber bundle by appropriately switching the backwash water supply and drainage when the deposited deposits are peeled off and flowed out of the system. Claim 1) is disclosed.

JP-A-8-332357

  The time for washing the filtration membrane can be controlled so that the treatment flow rate and filtration pressure are measured during operation, and the treatment flow rate is lowered or the filtration pressure is increased at a stage exceeding a predetermined value. However, if the processing amount (integrated value of the processing flow rate) or operation time at which the decrease in the processing flow rate or increase in the filtration pressure becomes a predetermined value can be predicted, the time or the operation time at which the predicted processing amount is reached automatically. A method of cleaning is also conceivable. According to this method, it is possible to more easily manage cleaning during operation.

  However, the treatment amount or operation time in which the decrease in the treatment flow rate or the increase in the filtration pressure becomes a predetermined value (that is, membrane clogging occurs due to the turbidity in the treated water) varies depending on the amount of turbidity in the treated water. To do. The amount of turbidity that clogs the membrane in the water to be treated, particularly seawater, varies greatly depending on the region and season. Therefore, a method for measuring the amount of turbidity in the water to be treated is desired, but a method for accurately measuring the amount of turbidity has not been found. As a result, there has been a problem that it is difficult to predict the treatment amount or operation time at which membrane clogging occurs due to the measurement of the water to be treated.

  The present invention measures the amount of water to be treated in membrane filtration of water to be treated containing jelly-like turbid components such as seawater, drainage, and ballast water, and the amount of treatment that causes clogging of the membrane based on the measured value Alternatively, it is an object of the present invention to provide a method for predicting a membrane clogging speed that enables prediction of operation time, and a filtration system capable of performing the prediction method.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has developed a method for measuring the amount of sugar in the water to be treated, and the amount of sugar measured by this method and the treatment that causes clogging of the filtration membrane. The present invention was completed by finding that there is a strong correlation between the quantity and the operating time.

  That is, according to the first aspect of the present invention, in the membrane filtration, the amount of sugar in the water to be treated is measured, and the clogging rate of the filtration membrane is calculated from the measured value. This is a prediction method.

  Here, the clogging speed of the filtration membrane refers to the integrated value of the processing flow rate or the reciprocal of the operation time after the start of the membrane filtration operation or after the filtration membrane is washed until the next washing is necessary. Specifically, it means the integrated value of the treatment flow rate or the reciprocal of the operation time until the decrease in the treatment flux or the increase in the filtration pressure exceeds the predetermined value after the membrane filtration operation is started or after the filtration membrane is washed. To do. The clogging speed of the membrane is originally represented by the reciprocal of the integrated value of the processing flow rate, but if there is no significant difference in the processing flux until the next cleaning, the next cleaning is necessary. Since the time until is always constant, it can be expressed by the reciprocal of the time.

  The method of the present invention is characterized in that the clogging speed of the filtration membrane is calculated from the measured value of the amount of sugar in the water to be treated. According to the study of the present inventors, it has been found that there is a strong correlation between the measured value of the amount of sugar in the treated water and the clogging rate of the filtration membrane. That is, as the measured value of the amount of sugar in the water to be treated increases, the clogging speed of the filtration membrane increases (the time until clogging is shorter). Therefore, the method of the present invention makes it possible to predict the clogging rate of the filtration membrane, that is, the time when the next cleaning is required.

  In addition to TEP, there are inorganic turbidity such as plankton and sand, and organic turbidity such as protein as turbidity in seawater, drainage and ballast water. In particular, TEP was thought to cause rapid clogging by swelling and covering the film surface even in a trace amount that is difficult to detect by weight measurement or TOC measurement. Then, although TEP removal from to-be-processed water was desired, since the amount of TEP was not able to be measured, research of TEP removal was very difficult. The present inventor pays attention to the fact that most of TEP is said to be sugars, and it is possible to predict the amount of TEP by performing sugar analysis, and the cause of clogging is mainly TEP. In the case (for example, when using a filtration membrane in which the cause of clogging is mainly TEP), it was considered that clogging speed can be predicted based on the measured value of the amount of sugar in the water to be treated. As a result, it was found that there is a strong correlation between the measured amount of sugar in the water to be treated and the clogging speed of the filtration membrane.

  Invention of Claim 2 is a prediction method of the clogging speed | rate of the filtration membrane of Claim 1 characterized by the to-be-processed water being seawater.

  The method of the present invention is suitably applied in membrane filtration of water to be treated containing jelly-like turbid components such as TEP such as seawater, drainage, ballast water, etc., but the cause of clogging of the filtration membrane is mainly used. In particular, it is effective and suitable for membrane filtration of seawater, which is said to be in TEP. Seawater here means not only water collected directly from the sea but also water that uses seawater such as ballast water as it is.

  The invention according to claim 3 is the method for predicting the clogging speed of the filtration membrane according to claim 1 or 2, wherein the sugar amount is measured by liquid chromatography of concentrated water to be treated. is there.

  As a method for measuring the amount of sugar, there is a method of concentrating the water to be treated, analyzing the obtained concentrated sample by liquid chromatography, particularly ion chromatography, and quantifying it based on the peak intensity of the sugar in the obtained chromatogram. Can be mentioned. Concentration of the water to be treated can be performed by a method of re-dissolving the residue after distillation of water in the water to be treated or freeze-drying the water to be treated with a small amount of pure water.

  In the case of ion chromatography, hydrolysis for changing the polysaccharide in the water to be treated into monosaccharide is performed before being subjected to quantification by liquid chromatography. In addition, as other pretreatments, filtration and centrifugation may be performed to remove turbidity in the water to be treated, and treatment with an ion exchange resin may be performed to remove ions dissolved in the water to be treated. .

  In the case of ion chromatography using an anion exchange resin, examples of the mobile phase include sodium hydroxide solution. As the detector, a suggestive refractometer or the like can be used, but in the case of ion chromatography, an electrochemical detector is preferably used.

  The invention according to claim 4 is characterized in that the amount of sugar is measured by measuring the amount of rhamnose, galactose, glucose and mannose by ion chromatography. This is a prediction method.

  The present inventor has found that in seawater analyzed so far, the sugar (polysaccharide) contained therein is formed from rhamnose, galactose, glucose and mannose. In this case, the sugar contained in seawater changes into rhamnose, galactose, glucose, and mannose by hydrolysis performed before being subjected to quantification by liquid chromatography in ion chromatography analysis. Therefore, the inventors have found that the total amount of these sugars measured by ion chromatography after the hydrolysis can be used as a measurement value of the sugar amount in the method of the present invention, and thus the invention according to claim 4 has been completed. is there.

  The invention according to claim 5 is a membrane filtration device for water to be treated, a means for measuring the amount of sugar in the water to be treated, and a clogging rate prediction for calculating the clogging rate of the filtration membrane from the measured value of sugar amount by the measuring means. And a filtration membrane cleaning means.

  The membrane filter for water to be treated constituting the present invention is used for removing turbid components contained in the water to be treated such as seawater, drainage, ballast water, etc. in seawater desalination and wastewater treatment. The thing similar to the conventional membrane filtration apparatus can be mentioned, For example, the membrane filtration apparatus using filtration membranes, such as a hollow fiber and a membrane, can be mentioned. Further, the filtration membrane cleaning means may be the one provided in the conventional membrane filtration device as described above.

  The sugar amount measurement means and the clogging speed prediction means in the water to be treated are means for executing a sugar amount measurement method and a clogging speed prediction method, respectively. These means are not particularly limited as long as the sugar amount measurement method and the clogging speed can be predicted as described in claims 1 to 4. A system for executing a method comprising a plurality of steps is also included in this means. For example, the step of sampling seawater, the step of pre-processing the sampled seawater, the step of measuring ion chromatography, and the data of ion chromatography measurements are processed, and the total amount of rhamnose, galactose, glucose and mannose is calculated. The sugar amount measuring system comprising the calculating step is also a means for measuring the sugar amount in the water to be treated.

  The filtration system according to claim 5 measures the sugar amount in the water to be treated and predicts the clogging speed (that is, the method of the present invention), and determines the timing of cleaning the filtration membrane based on the prediction result. Judgment is performed, and the membrane is cleaned by a filtration membrane cleaning means. Therefore, it is possible to prevent a large decrease in the flux due to clogging and perform stable filtration. Note that “determining when to wash the filtration membrane based on the prediction result” does not necessarily mean always measuring the amount of sugar or predicting the clogging rate during membrane filtration. At the start of the filtration membrane, measure the amount of sugar and predict the clogging rate, and enter the data into a management means that can be installed in the filtration system. This also includes the case where the speed of the membrane is determined based on the data alone without predicting the speed.

  According to the method for predicting the clogging rate of the filtration membrane of the present invention, clogging of the filtration membrane due to turbidity is caused after the start of the membrane filtration operation or after the filtration membrane is washed based on the measured value of the amount of sugar in the treated water. The integrated value of the treatment flow rate or the operation time until the next membrane cleaning is required can be predicted, and therefore the time when the next cleaning is required can be predicted. It becomes easy. In addition, according to the filtration system of the present invention, the time when the filtration needs to be washed can be predicted with high accuracy, so that a large decrease in the flux due to clogging can be prevented and stable filtration can be performed.

It is a schematic diagram which shows the internal structure of the membrane filtration apparatus with which this invention is applied. It is the graph which showed the time change of the "flux / initial flux" in the membrane filtration of an Example.

  Next, the form for implementing this invention is demonstrated concretely. Note that the present invention is not limited to this form, and can be changed to other forms as long as the gist of the present invention is not impaired.

  Membrane filtration to which the present invention is applied can be performed by a membrane filtration apparatus using a module equipped with a filtration membrane. This membrane filtration apparatus has a filtration membrane cleaning means together with a module. FIG. 1 is a diagram schematically showing the internal structure of an example of a membrane filtration device to which the present invention is applied. The membrane filtration apparatus of FIG. 1 includes a module at the center of a cylindrical case, and a hollow fiber bundle (not shown) in which a plurality of hollow fiber membranes as a filtration membrane are bundled is accommodated in this module. . In addition, although the form of a filtration membrane is not limited to a hollow fiber membrane, forms, such as a membrane, can also be mentioned, In order to increase a throughput with a wider membrane area, a hollow fiber membrane is preferable.

  The membrane filtration device of FIG. 1 further includes three shower devices as filtration membrane cleaning means, and is not shown, but from a direction opposite to the means for supplying the treated water and the flow of the treated water. Means for supplying cleaning water are provided. Each shower device has a plurality of (four in the figure) nozzles, and a shower is sprayed from the nozzles onto the surface of the module, that is, the hollow fiber bundle, to clean the membrane.

  Therefore, the membrane filtration apparatus of FIG. 1 has a membrane filtration apparatus for water to be treated and a filtration membrane cleaning means in the filtration system of the present invention. The filtration system of the present invention further comprises a means for measuring the amount of sugar in the water to be treated, and a clogging rate prediction means for calculating the clogging rate of the filtration membrane from the measured value of the amount of sugar by the measuring means.

  When membrane filtration of seawater or the like is performed, water to be treated such as seawater is supplied between the cylindrical case and the module, passes through the hollow fiber membrane, and is discharged from the inside of the module (inside the hollow fiber) as processing liquid to the outside of the apparatus. . When passing through the hollow fiber membrane, turbid components such as TEP are removed. At this time, the hollow fiber membrane is clogged with turbid components, the treatment flow rate is lowered, and the filtration pressure (differential pressure) is increased.

  Therefore, in order to recover the treatment flow rate (or filtration pressure), the hollow fiber membrane is washed. According to the method of the present invention, the next hollow fiber membrane is based on the measured value of the amount of sugar in the treated water. It is possible to predict the time when the cleaning is required. By washing the hollow fiber membrane, recovery of the treatment flow rate and reduction of the differential pressure are achieved, and then the flow of water to be treated is resumed in the same manner as described above.

  In membrane filtration of water to be treated containing jelly-like turbid components such as TEP, when a hydrophobic filtration membrane made of a hydrophobic material and having a relatively large pore size is used, clogging tends to be small. . A hydrophobic filtration membrane having a relatively large pore size, specifically about 1 μm or larger, is considered to be because the jelly-like turbid component is less likely to stick to the surface and clogging is difficult. In addition, since TEP is a jelly-like particle having a particle size of about 1 to 200 μm, the jelly-like turbid component sticks and spreads on the membrane surface or pores in membrane filtration of water to be treated containing this. It is thought that the hydrophobic filtration membrane having a relatively large pore diameter draws TEP into the inside of the membrane for separation, although it is easy to foul the pores (clogging). As a result, it is possible to efficiently remove TEP that cannot be sufficiently removed by a film that cuts turbidity on the film surface.

  More specifically, the hydrophobic filtration membrane is a membrane made of a hydrophobic polymer material and not subjected to hydrophilization processing (introduction of a hydrophilic group into the hydrophobic polymer). A membrane having pores with a uniform diameter so that it can be used as a filtration membrane. Examples of the hydrophobic polymer material constituting the hydrophobic filtration membrane include a fluororesin and a polyolefin. Examples of the fluororesin include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF). Examples of the polyolefin include polyethylene and other poly-α-olefins. Among these, since the film | membrane which consists of a fluororesin or polyethylene is excellent in chemical resistance and mechanical strength, it is used suitably as a hydrophobic filtration membrane in this invention.

Membrane filtration 1
Seawater (freshwater seawater) was filtered through a wire mesh having an opening of 2 μm, and membrane filtration was performed using a membrane filtration apparatus having the following specifications and the structure shown in FIG. 1 (two-stage filtration). . FIG. 2 shows the time variation of the “flux / initial flux” at that time.

[specification]
Module diameter: 40mm
Hollow fiber membrane in module: 10 modules Length: 40cm
Hollow fiber membrane: Porefluoron (PTFE) manufactured by Sumitomo Electric Fine Polymer,
Diameter: 2.3 mm, hole diameter: 0.1 μm (MF membrane)

Membrane filtration 2
Instead of filtration with a wire mesh having a mesh opening of 2 μm, the membrane filtration was carried out in the same manner as the membrane filtration 1 except that the membrane filtration was carried out using the membrane filtration device having the following specification and the structure shown in FIG. Two-stage filtration was performed. FIG. 2 shows the time variation of the “flux / initial flux” at that time.

[specification]
Module diameter: 40mm
Hollow fiber membrane in module: 10 modules Length: 40cm
Hollow fiber membrane: Porefluoron (PTFE) manufactured by Sumitomo Electric Fine Polymer,
Diameter: 2.3 mm, hole diameter: 2 μm

Membrane filtration 3
Instead of a hollow fiber membrane having a pore diameter of 2 μm, a hollow fiber membrane (diameter: 2.3 mm, pore diameter: made of Sumitomo Electric Fine Polymer's hydrophilic poreflon (poreflon having a hydrophilic group introduced on the polymer surface constituting the membrane). Two-stage filtration was performed in the same manner as the membrane filtration 2 except that 2 μm) was used. FIG. 2 shows the time variation of the “flux / initial flux” at that time.

Membrane filtration 4
Filtration was carried out in the same manner as in membrane filtration 1 except that filtration through a wire mesh having an opening of 2 μm was not performed. FIG. 2 shows the time variation of the “flux / initial flux” at that time.

  Treated water used for membrane filtration by the second-stage MF membrane in membrane filtration 1 to 4 (treated water after first-stage filtration in membrane filtration 1 to 3, and seawater in membrane filtration 4. ) Was measured by the analytical test method shown below. The results are shown in Table 1.

(Analytical test method)
1. Sample Concentration After 100 mL of each sample of membrane filtration 1 to 4 was lyophilized, it was washed with pure water to make exactly 10 mL to obtain a concentrated sample.

2. Sugar analysis (1) Preparation of sample solution 1 mL of the concentrated sample prepared in step 1 and 1 mL of 4 mol / L trifluoroacetic acid were mixed, and after sealed under reduced pressure, heated at 100 ° C. for 3 hours to perform hydrolysis (polysaccharide → monosaccharide).

  After cooling to room temperature, the solvent was distilled off with a centrifugal evaporator. 1 mL of water was accurately added to the residue, and ultrasonic waves were applied to promote dispersion and dissolution. The obtained solution was put into a filter unit (pore size: 0.45 μm) containing an ion exchange resin (AG4-X4), and centrifuged (10,000 rpm) for 1 minute to obtain a sample solution.

  Hereinafter, the sample in the membrane filtration 1 is “wire mesh permeate”, the sample in the membrane filtration 2 is “hydrophobic membrane permeate”, the sample in the membrane filtration 3 is “hydrophilic membrane permeate”, and the membrane filtration 3 The sample is represented as “seawater”.

(2) Preparation of standard solution Water was added to about 10 mg each of rhamnose, galactose, glucose and mannose to make exactly 50 mL. 5 mL of this solution was accurately taken, and water was added to make exactly 50 mL to obtain a standard stock solution. The standard stock solution was accurately diluted with water to prepare standard solution 1 (about 0.2 μg / mL each), standard solution 2 (about 1 μg / mL each), and standard solution 3 (about 5 μg / mL each).

(3) Quantification of sugar For each sample solution, standard solutions 1 to 3, and a solution obtained by mixing each of the sample solution and standard solutions 1 to 3, ion chromatography analysis was performed under the following measurement conditions. Identification and quantification of sugars in the sample solution was performed. The quantitative results are shown in Table 1.

(Measurement condition)
Sugar analyzer: ICS-3000 manufactured by Nippon Dionex
Detector: Electrochemical detector Column: CarboPac PA10 (4 mm ID x 250 mm)
Column temperature: constant temperature around 25 ° C. Mobile phase A: 10 mmol / L sodium hydroxide solution Mobile layer B: 200 mmol / L sodium hydroxide solution Injection volume: 25 μL, flow rate: 1 mL
Gradient condition: mobile phase A for 40 minutes → mobile phase B for 10 minutes → mobile phase A for 10 minutes

  “Total” in Table 1 is the total amount of measured values of rhamnose amount, galactose amount, glucose amount, and mannose amount. The “sugar removal rate” represents the rate of decrease with respect to “seawater” with respect to this total amount. As is clear from Table 1, the hydrophobic membrane permeated water has a smaller measured sugar amount (total amount) and a larger sugar removal rate than the hydrophilic membrane permeated water and the wire mesh permeated water (depending on the hydrophobic membrane). Sugar is well removed).

  Further, from FIG. 2, membrane filtration 2 (hydrophobic membrane permeated water filtration) in which the first-stage filtration was performed with a hydrophobic filtration membrane, membrane filtration 3 (hydrophilicity) in which the first-stage filtration was performed with a hydrophilic filtration membrane. Compared with membrane filtration 1 (filtration of the permeated water of the membrane) and membrane filtration 1 (filtration of the permeated water of the metal mesh) performed by the first stage filtration, the decrease in the flux during operation is small, and therefore the clogging speed of the filtration membrane is reduced. It is shown that the cleaning frequency may be small. That is, from the results of Table 1 and FIG. 2, the sugar content (sugar content) and the clogging speed of the filtration membrane have a large correlation, and the clogging speed of the filtration membrane can be predicted by measuring the sugar content. It is shown.

Claims (5)

  In membrane filtration, a method for predicting the clogging rate of a filtration membrane, comprising measuring the amount of sugar in the water to be treated and calculating the clogging rate of the filtration membrane from the measured value.   The method for predicting the clogging speed of a filtration membrane according to claim 1, wherein the water to be treated is seawater.   The method for predicting the clogging rate of a filtration membrane according to claim 1 or 2, wherein the sugar amount is measured by liquid chromatography of concentrated water to be treated.   The method for predicting the clogging rate of a filtration membrane according to claim 3, wherein the measurement of the amount of sugar is measurement of the amount of rhamnose, galactose, glucose and mannose by ion chromatography.   A membrane filtration device for water to be treated, a means for measuring the amount of sugar in the water to be treated, a clogging speed predicting means for calculating a clogging speed of the filtration membrane from a measurement value of the sugar amount by the measuring means, and a filtration membrane washing means A filtration system characterized by that.

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